Efficacy of indoor residual spraying with dichlorodiphenyltrichloroethane against malaria in Gambian communities with high usage of long-lasting insecticidal mosquito nets: a cluster-randomised controlled trial

A systematic review of sample size estimation accuracy on power in malaria cluster randomised trials measuring epidemiological outcomes

INTRODUCTION

Cluster randomised trials (CRTs) are the gold standard for measuring the community-wide impacts of malaria control tools. CRTs rely on well-defined sample size estimations to detect statistically significant effects of trialled interventions, however these are often predicted poorly by triallists. Here, we review the accuracy of predicted parameters used in sample size calculations for malaria CRTs with epidemiological outcomes.

METHODS

We searched for published malaria CRTs using four online databases in March 2022. Eligible trials included those with malaria-specific epidemiological outcomes which randomised at least six geographical clusters to study arms. Predicted and observed sample size parameters were extracted by reviewers for each trial. Pair-wise Spearman's correlation coefficients (rs) were calculated to assess the correlation between predicted and observed control-arm outcome measures and effect sizes (relative percentage reductions) between arms. Among trials which retrospectively calculated an estimate of heterogeneity in cluster outcomes, we recalculated study power according to observed trial estimates.

RESULTS

Of the 1889 records identified and screened, 108 articles were eligible and comprised of 71 malaria CRTs. Among 91.5% (65/71) of trials that included sample size calculations, most estimated cluster heterogeneity using the coefficient of variation (k) (80%, 52/65) which were often predicted without using prior data (67.7%, 44/65). Predicted control-arm prevalence moderately correlated with observed control-arm prevalence (rs: 0.44, [95%CI: 0.12,0.68], p-value < 0.05], with 61.2% (19/31) of prevalence estimates overestimated. Among the minority of trials that retrospectively calculated cluster heterogeneity (20%, 13/65), empirical values contrasted with those used in sample size estimations and often compromised study power. Observed effect sizes were often smaller than had been predicted at the sample size stage (72.9%, 51/70) and were typically higher in the first, compared to the second, year of trials. Overall, effect sizes achieved by malaria interventions tested in trials decreased between 1995 and 2021.

CONCLUSIONS

Study findings reveal sample size parameters in malaria CRTs were often inaccurate and resulted in underpowered studies. Future trials must strive to obtain more representative epidemiological sample size inputs to ensure interventions against malaria are adequately evaluated.

REGISTRATION

This review is registered with PROSPERO (CRD42022315741).

Field performance of three mosquito collection methods for assessing the entomological efficacy of dual-active ingredient long-lasting insecticidal nets

Selection of mosquito collection methods is of crucial importance to evaluate the impact of vector control tools on entomological outcomes. During a cluster randomised control trial evaluating the relative efficacy of two dual-active ingredient (a.i.) long-lasting insecticidal nets (LLINs) compared to pyrethroid-only LLINs, we assessed the performance of different mosquito collection methods: Human landing catches (HLC), Centers for Disease Control and Prevention (CDC) light traps, and pyrethrum spray catches (PSC). Anopheles mosquitoes were collected using three collection methods in 4 houses, in each of the 60 trial clusters at baseline and every quarter for 24 months using PSCs and HLCs, while CDC light traps were performed during two quarters only. Mean density of vectors collected per method per night was the highest with HLCs (15.9), followed by CDC light traps (6.8); with PSCs (1.1) collecting 10 times less mosquitoes than HLCs. All three collection methods collected fewer mosquitoes in the Interceptor G2® dual a.i. arm, compared to the other trial arms, although only HLCs and PSCs demonstrated strong evidence of this due to a greater number of collection rounds undertaken, than CDC light traps. The broadly similar results regarding the differential impact of the two dual a.i. LLINs showed by the three collection methods suggest that the more ethically acceptable, cheaper, and logistically simpler methods such as CDC light traps could be prioritised for use in large community trials for measuring the efficacy of vector control tools.

Distribution of Anopheles gambiae thioester-containing protein 1 alleles along malaria transmission gradients in The Gambia

BACKGROUND

Thioester-containing protein 1 (TEP1) is a highly polymorphic gene playing an important role in mosquito immunity to parasite development and associated with Anopheles gambiae vectorial competence. Allelic variations in TEP1 could render mosquito either susceptible or resistant to parasite infection. Despite reports of TEP1 genetic variations in An. gambiae, the correlation between TEP1 allelic variants and transmission patterns in malaria endemic settings remains unclear.

METHODS

TEP1 allelic variants were characterized by PCR from archived genomic DNA of > 1000 An. gambiae mosquitoes collected at 3 time points between 2009 and 2019 from eastern Gambia, where malaria transmission remains moderately high, and western regions with low transmission.

RESULTS

Eight common TEP1 allelic variants were identified at varying frequencies in An. gambiae from both transmission settings. These comprised the wild type TEP1, homozygous susceptible genotype, TEP1s; homozygous resistance genotypes: TEP1rA and TEP1rB, and the heterozygous resistance genotypes: TEP1srA, TEP1srB, TEP1rArB and TEP1srArB. There was no significant disproportionate distribution of the TEP1 alleles by transmission setting and the temporal distribution of alleles was also consistent across the transmission settings. TEP1s was the most common in all vector species in both settings (allele frequencies: East = 21.4-68.4%. West = 23.5-67.2%). In Anopheles arabiensis, the frequency of wild type TEP1 and susceptible TEP1s was significantly higher in low transmission setting than in high transmission setting (TEP1: Z = - 4.831, P < 0.0001; TEP1s: Z = - 2.073, P = 0.038).

CONCLUSIONS

The distribution of TEP1 allele variants does not distinctly correlate with malaria endemicity pattern in The Gambia. Further studies are needed to understand the link between genetic variations in vector population and transmission pattern in the study settings. Future studies on the implication for targeting TEP1 gene for vector control strategy such as gene drive systems in this settings is also recommended.

Integrated malaria prevention in low- and middle-income countries: a systematic review

BACKGROUND

As many countries aim to eliminate malaria, use of comprehensive approaches targeting the mosquito vector and environment are needed. Integrated malaria prevention advocates the use of several malaria prevention measures holistically at households and in the community. The aim of this systematic review was to collate and summarize the impact of integrated malaria prevention in low- and middle-income countries on malaria burden.

METHODS

Literature on integrated malaria prevention, defined as the use of two or more malaria prevention methods holistically, was searched from 1st January 2001 to 31st July 2021. The primary outcome variables were malaria incidence and prevalence, while the secondary outcome measures were human biting and entomological inoculation rates, and mosquito mortality.

RESULTS

A total of 10,931 studies were identified by the search strategy. After screening, 57 articles were included in the review. Studies included cluster randomized controlled trials, longitudinal studies, programme evaluations, experimental hut/houses, and field trials. Various interventions were used, mainly combinations of two or three malaria prevention methods including insecticide-treated nets (ITNs), indoor residual spraying (IRS), topical repellents, insecticide sprays, microbial larvicides, and house improvements including screening, insecticide-treated wall hangings, and screening of eaves. The most common methods used in integrated malaria prevention were ITNs and IRS, followed by ITNs and topical repellents. There was reduced incidence and prevalence of malaria when multiple malaria prevention methods were used compared to single methods. Mosquito human biting and entomological inoculation rates were significantly reduced, and mosquito mortality increased in use of multiple methods compared to single interventions. However, a few studies showed mixed results or no benefits of using multiple methods to prevent malaria.

CONCLUSION

Use of multiple malaria prevention methods was effective in reducing malaria infection and mosquito density in comparison with single methods. Results from this systematic review can be used to inform future research, practice, policy and programming for malaria control in endemic countries.

Inferring the epidemiological benefit of indoor vector control interventions against malaria from mosquito data

The cause of malaria transmission has been known for over a century but it is still unclear whether entomological measures are sufficiently reliable to inform policy decisions in human health. Decision-making on the effectiveness of new insecticide-treated nets (ITNs) and the indoor residual spraying of insecticide (IRS) have been based on epidemiological data, typically collected in cluster-randomised control trials. The number of these trials that can be conducted is limited. Here we use a systematic review to highlight that efficacy estimates of the same intervention may vary substantially between trials. Analyses indicate that mosquito data collected in experimental hut trials can be used to parameterize mechanistic models for Plasmodium falciparum malaria and reliably predict the epidemiological efficacy of quick-acting, neuro-acting ITNs and IRS. Results suggest that for certain types of ITNs and IRS using this framework instead of clinical endpoints could support policy and expedite the widespread use of novel technologies.

Implementation and acceptance of government-sponsored malaria control interventions in Meghalaya, India

Background

India has made considerable progress in malaria reduction over the past two decades, with government-sponsored indoor residual spraying (IRS) and insecticide-treated bed net (ITN) or long-lasting insecticidal nets (LLIN) distribution being the main vector-related prevention efforts. Few investigations have used non-participant observational methods to assess malaria control measures while they were being implemented, nor documented people’s perceptions and acceptance of IRS or LLINs in India, and none have done so in the northeast region. This study evaluated household (HH)-level operation of IRS and distribution of LLINs by India’s National Vector Borne Disease Control Programme (NVBDCP) in 50 villages of Meghalaya state, and documented their acceptance and use.

Methods

Study field teams accompanied the government health system teams during August-October, 2019 and 2020 to observe deployment of LLINs, and record HH-level data on LLIN numbers and use. In addition, NVBDCP spray teams were followed during 2019–2021 to observe IRS preparation and administration. HH members were interviewed to better understand reasons for acceptance or refusal of spraying.

Results

A total of 8386 LLINs were distributed to 2727 HHs in 24 villages from five Primary Health Centres, representing 99.5% of planned coverage. Interviews with 80 HH residents indicated that they appreciated the LLIN dissemination programme, and generally made regular and appropriate use of LLINs, except during overnight travel or when working in agricultural fields. However, HH-level IRS application, which was observed at 632 HHs, did not always follow standard insecticide preparation and safety protocols. Of 1,079 occupied HHs visited by the spray team, 632 (58.6%) refused to allow any spraying. Only 198 (18.4%) HHs agreed to be sprayed, comprising 152 (14.1%) that were only partly sprayed, and 46 (4.3%) that were fully sprayed. Reasons for refusal included: inadequate time to rearrange HH items, young children were present, annoying smell, staining of walls, and threat to bee-keeping or Eri silk moth cultivation.

Conclusions

These findings are among the first in India that independently evaluate people's perceptions and acceptance of ongoing government-sponsored IRS and LLIN programmes for malaria prevention. They represent important insights for achieving India's goal of malaria elimination by 2030.

Reduction in malaria burden following the introduction of indoor residual spraying in areas protected by long-lasting insecticidal nets in Western Kenya, 2016-2018

Background

Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the main malaria vector control measures deployed in Kenya. Widespread pyrethroid resistance among the primary vectors in Western Kenya has necessitated the re-introduction of IRS using an organophosphate insecticide, pirimiphos-methyl (Actellic® 300CS), as a pyrethroid resistance management strategy. Evaluation of the effectiveness of the combined use of non-pyrethroid IRS and LLINs has yielded varied results. We aimed to evaluate the effect of non-pyrethroid IRS and LLINs on malaria indicators in a high malaria transmission area.

Methods

We reviewed records and tallied monthly aggregate of outpatient department (OPD) attendance, suspected malaria cases, those tested for malaria and those testing positive for malaria at two health facilities, one from Nyatike, an intervention sub-county, and one from Suba, a comparison sub-county, both located in Western Kenya, from February 1, 2016, through March 31, 2018. The first round of IRS was conducted in February–March 2017 in Nyatike sub-county and the second round one year later in both Nyatike and Suba sub-counties. The mass distribution of LLINs has been conducted in both locations. We performed descriptive analysis and estimated the effect of the interventions and temporal changes of malaria indicators using Poisson regression for a period before and after the first round of IRS.

Results

A higher reduction in the intervention area in total OPD, the proportion of OPD visits due to suspected malaria, testing positivity rate and annual malaria incidences were observed except for the total OPD visits among the under 5 children (59% decrease observed in the comparison area vs 33% decrease in the intervention area, net change -27%, P <0.001). The percentage decline in annual malaria incidence observed in the intervention area was more than twice the observed percentage decline in the comparison area across all the age groups. A marked decline in the monthly testing positivity rate (TPR) was noticed in the intervention area, while no major changes were observed in the comparison area. The monthly TPR reduced from 46% in February 2016 to 11% in February 2018, representing a 76% absolute decrease in TPR among all ages (RR = 0.24, 95% CI 0.12–0.46). In the comparison area, TPR was 16% in both February 2016 and February 2018 (RR = 1.0, 95% CI 0.52–2.09). A month-by-month comparison revealed lower TPR in Year 2 compared to Year 1 in the intervention area for most of the one year after the introduction of the IRS.

Conclusions

Our findings demonstrated a reduced malaria burden among populations protected by both non-pyrethroid IRS and LLINs implying a possible additional benefit afforded by the combined intervention in the malaria-endemic zone.

Mass drug administration of ivermectin and dihydroartemisinin-piperaquine against malaria in settings with high coverage of standard control interventions: a cluster-randomised controlled trial in The Gambia

BACKGROUND

Although the malaria burden has substantially decreased in sub-Saharan Africa, progress has stalled. We assessed whether mass administration of ivermectin (a mosquitocidal drug) and dihydroartemisinin-piperaquine (an antimalarial treatment) reduces malaria in The Gambia, an area with high coverage of standard control interventions.

METHODS

This open-label, cluster-randomised controlled trial was done in the Upper River region of eastern Gambia. Villages with a baseline Plasmodium falciparum prevalence of 7-46% (all ages) and separated from each other by at least 3 km to reduce vector spillover were selected. Inclusion criteria were age and anthropometry (for ivermectin, weight of ≥15 kg; for dihydroartemisinin-piperaquine, participants older than 6 months); willingness to comply with trial procedures; and written informed consent. Villages were randomised (1:1) to either the intervention (ivermectin [orally at 300-400 μg/kg per day for 3 consecutive days] and dihydroartemisinin-piperaquine [orally depending on bodyweight] plus standard control interventions) or the control group (standard control interventions) using computer-based randomisation. Laboratory staff were masked to the origin of samples. In the intervention group, three rounds of mass drug administration once per month with ivermectin and dihydroartemisinin-piperaquine were given during two malaria transmission seasons from Aug 27 to Oct 31, 2018, and from July 15 to Sept 30, 2019. Primary outcomes were malaria prevalence by qPCR at the end of the second intervention year in November 2019, and Anopheles gambiae (s l) parous rate, analysed in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, NCT03576313.

FINDINGS

Between Nov 20 and Dec 7, 2017, 47 villages were screened for eligibility in the study. 15 were excluded because the baseline malaria prevalence was less than 7% (figure 1). 32 villages were enrolled and randomised to either the intervention or control group (n=16 in each group). The study population was 10 638, of which 4939 (46%) participants were in intervention villages. Coverage for dihydroartemisinin-piperaquine was between 49·0% and 58·4% in 2018, and between 76·1% and 86·0% in 2019; for ivermectin, coverage was between 46·9% and 52·2% in 2018, and between 71·7% and 82·9% in 2019. In November 2019, malaria prevalence was 12·8% (324 of 2529) in the control group and 5·1% (140 of 2722) in the intervention group (odds ratio [OR] 0·30, 95% CI 0·16-0·59; p<0·001). A gambiae (s l) parous rate was 83·1% (552 of 664) in the control group and 81·7% (441 of 540) in the intervention group (0·90, 0·66-1·25; p=0·537). In 2019, adverse events were recorded in 386 (9·7%) of 3991 participants in round one, 201 (5·4%) of 3750 in round two, and 168 (4·5%) of 3752 in round three. None of the 11 serious adverse events were related to the intervention.

INTERPRETATION

The intervention was safe and well tolerated. In an area with high coverage of standard control interventions, mass drug administration of ivermectin and dihydroartemisinin-piperaquine significantly reduced malaria prevalence; however, no effect of ivermectin on vector parous rate was observed.

FUNDING

Joint Global Health Trials Scheme.

TRANSLATION

For the French translation of the abstract see Supplementary Materials section.

Indoor residual spraying for preventing malaria in communities using insecticide-treated nets

BACKGROUND

Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) are used to prevent malaria transmission. Both interventions use insecticides to kill mosquitoes that bite and rest indoors. Adding IRS to ITNs may improve malaria control simply because two interventions can be better than one. Furthermore, IRS may improve malaria control where ITNs are failing due to insecticide resistance. Pyrethroid insecticides are the predominant class of insecticide used for ITNs, as they are more safe than other insecticide classes when in prolonged contact with human skin. While many mosquito populations have developed some resistance to pyrethroid insecticides, a wider range of insecticides can be used for IRS. This review is an update of the previous Cochrane 2019 edition.

OBJECTIVES

To summarize the effect on malaria of additionally implementing IRS, using non-pyrethroid-like or pyrethroid-like insecticides, in communities currently using ITNs.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register; CENTRAL; MEDLINE; and five other databases for records from 1 January 2000 to 8 November 2021, on the basis that ITN programmes did not begin to be implemented as policy before the year 2000.

SELECTION CRITERIA

We included cluster-randomized controlled trials (cRCTs), interrupted time series (ITS), or controlled before-after studies (CBAs) comparing IRS plus ITNs with ITNs alone. We included studies with at least 50% ITN ownership (defined as the proportion of households owning one or more ITN) in both study arms.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility, analyzed risk of bias, and extracted data. We used risk ratio (RR) and 95% confidence intervals (CI). We stratified by type of insecticide, 'pyrethroid-like' and 'non-pyrethroid-like'; the latter could improve malaria control better than adding IRS insecticides that have the same way of working as the insecticide on ITNs ('pyrethroid-like'). We used subgroup analysis of ITN usage in the studies to explore heterogeneity. We assessed the certainty of evidence using the GRADE approach.

MAIN RESULTS

Eight cRCTs (10 comparisons), one CBA, and one ITS study, all conducted since 2008 in sub-Saharan Africa, met our inclusion criteria. The primary vectors in all sites were mosquitoes belonging to the Anopheles gambiae s.l. complex species; five studies in Benin, Mozambique, Ghana, Sudan, and Tanzania also reported the vector Anopheles funestus. Five cRCTs and both quasi-experimental design studies used insecticides with targets different to pyrethroids (two used bendiocarb, three used pirimiphos-methyl, and one used propoxur. Each of these studies were conducted in areas where the vectors were described as resistant or highly resistant to pyrethroids. Two cRCTs used dichloro-diphenyl-trichlorethane (DDT), an insecticide with the same target as pyrethroids. The remaining cRCT used both types of insecticide (pyrethroid deltamethrin in the first year, switching to bendiocarb for the second year). Indoor residual spraying using 'non-pyrethroid-like' insecticides Six studies were included (four cRCTs, one CBA, and one ITS). Our main analysis for prevalence excluded a study at high risk of bias due to repeated sampling of the same population. This risk did not apply to other outcomes. Overall, the addition of IRS reduced malaria parasite prevalence (RR 0.61, 95% CI 0.42 to 0.88; 4 cRCTs, 16,394 participants; high-certainty evidence). IRS may also reduce malaria incidence on average (rate ratio 0.86, 95% CI 0.61 to 1.23; 4 cRCTs, 323,631 child-years; low-certainty evidence) but the effect was absent in two studies. Subgroup analyses did not explain the qualitative heterogeneity between studies. One cRCT reported no effect on malaria incidence or parasite prevalence in the first year, when a pyrethroid-like insecticide was used for IRS, but showed an effect on both outcomes in the second year, when a non-pyrethroid-like IRS was used. The addition of IRS may also reduce anaemia prevalence (RR 0.71, 95% CI 0.38 to 1.31; 3 cRCTs, 4288 participants; low-certainty evidence). Four cRCTs reported the impact of IRS on entomological inoculation rate (EIR), with variable results; overall, we do not know if IRS had any effect on the EIR in communities using ITNs (very low-certainty evidence). Studies also reported the adult mosquito density and the sporozoite rate, but we could not summarize or pool these entomological outcomes due to differences in the reported data. Three studies measured the prevalence of pyrethroid resistance before and after IRS being introduced: there was no difference detected, but these data are limited. Indoor residual spraying using 'pyrethroid-like' insecticides Adding IRS using a pyrethroid-like insecticide did not appear to markedly alter malaria incidence (rate ratio 1.07, 95% CI 0.80 to 1.43; 2 cRCTs, 15,717 child-years; moderate-certainty evidence), parasite prevalence (RR 1.11, 95% CI 0.86 to 1.44; 3 cRCTs, 10,820 participants; moderate-certainty evidence), or anaemia prevalence (RR 1.12, 95% CI 0.89 to 1.40; 1 cRCT, 4186 participants; low-certainty evidence). Data on EIR were limited so no conclusion was made (very low-certainty evidence).

AUTHORS' CONCLUSIONS

in communities using ITNs, the addition of IRS with 'non-pyrethroid-like' insecticides was associated with reduced malaria prevalence. Malaria incidence may also be reduced on average, but there was unexplained qualitative heterogeneity, and the effect may therefore not be observed in all settings. When using 'pyrethroid-like' insecticides, there was no detectable additional benefit of IRS in communities using ITNs.

A systematic review assessing the potential for release of vector species from competition following insecticide-based population suppression of Anopheles species in Africa

BACKGROUND

While insecticide-based vector control can effectively target vector species in areas of high malaria endemicity, such as Anopheles gambiae in Africa, residual disease transmission can occur. Understanding the potential role of competitive displacement between vector species could inform both current insecticide-based vector control programmes and the development of future complementary interventions.

METHODS

A systematic review was conducted to identify published studies of insecticide-based vector control of Anopheles species in Africa that reported indices for absolute densities of vector species. After screening against inclusion, exclusion and risk of bias criteria, studies were assigned to three categories based on whether they showed population density changes involving decreases in two or more vector species (D), increases in two or more vector species (I), or increases in one vector species concomitant with decreases in another vector species (ID). Category ID studies could thus provide evidence consistent with the release of vector species from competition following the insecticide-based population suppression of Anopheles species.

RESULTS

Of 5569 papers identified in searches, 30 were selected for quantitative and qualitative analysis. Nineteen studies were assigned to category D and one to category I. Ten studies categorised as ID provided evidence ranging from weak to persuasive that release from competition could have contributed to changes in species composition. Category ID showed no statistical differences from category D for reductions in malaria transmission and levels of insecticide resistance, but did so for insecticide type, pyrethroids being associated with category ID. A qualitative assessment identified five studies that provided the most convincing evidence that release from competition could have contributed to changes in species composition.

CONCLUSIONS

This review identified evidence that insecticide-based reductions in the density of Anopheles species in Africa could facilitate the release of other vector species from competition. While it remains uncertain whether this evidence is representative of most entomological sequelae of insecticide-based vector control in the field, five studies provided persuasive evidence that insecticide use could lead, at least under some circumstances, to competitive release of non-targeted vector species. These results should inform current and future integrated vector management approaches to malaria control.

Influence of insecticide resistance on the biting and resting preferences of malaria vectors in the Gambia

Background

The scale-up of indoor residual spraying and long-lasting insecticidal nets, together with other interventions have considerably reduced the malaria burden in The Gambia. This study examined the biting and resting preferences of the local insecticide-resistant vector populations few years following scale-up of anti-vector interventions.

Method

Indoor and outdoor-resting Anopheles gambiae mosquitoes were collected between July and October 2019 from ten villages in five regions in The Gambia using pyrethrum spray collection (indoor) and prokopack aspirator from pit traps (outdoor). Polymerase chain reaction assays were performed to identify molecular species, insecticide resistance mutations, Plasmodium infection rate and host blood meal.

Results

A total of 844 mosquitoes were collected both indoors (421, 49.9%) and outdoors (423, 50.1%). Four main vector species were identified, including An. arabiensis (indoor: 15%, outdoor: 26%); An. coluzzii (indoor: 19%, outdoor: 6%), An. gambiae s.s. (indoor: 11%, outdoor: 16%), An. melas (indoor: 2%, outdoor: 0.1%) and hybrids of An. coluzzii-An. gambiae s.s (indoors: 3%, outdoors: 2%). A significant preference for outdoor resting was observed in An. arabiensis (Pearson X² = 22.7, df = 4, P<0.001) and for indoor resting in An. coluzzii (Pearson X² = 55.0, df = 4, P<0.001). Prevalence of the voltage-gated sodium channel (Vgsc)-1014S was significantly higher in the indoor-resting (allele freq. = 0.96, 95%CI: 0.78–1, P = 0.03) than outdoor-resting (allele freq. = 0.82, 95%CI: 0.76–0.87) An. arabiensis population. For An. coluzzii, the prevalence of most mutation markers was higher in the outdoor (allele freq. = 0.92, 95%CI: 0.81–0.98) than indoor-resting (allele freq. = 0.78, 95%CI: 0.56–0.86) mosquitoes. However, in An. gambiae s.s., the prevalence of Vgsc-1014F, Vgsc-1575Y and GSTe2-114T was high (allele freq. = 0.96–1), but did not vary by resting location. The overall sporozoite positivity rate was 1.3% (95% CI: 0.5–2%) in mosquito populations. Indoor-resting An. coluzzii had mainly fed on human blood while indoor-resting An. arabiensis fed on animal blood.

Conclusion

In this study, high levels of resistance mutations were observed that could be influencing the mosquito populations to rest indoors or outdoors. The prevalent animal-biting behaviour demonstrated in the mosquito populations suggest that larval source management could be an intervention to complement vector control in this setting.

Modelling of malaria risk, rates, and trends: A spatiotemporal approach for identifying and targeting sub-national areas of high and low burden

While mortality from malaria continues to decline globally, incidence rates in many countries are rising. Within countries, spatial and temporal patterns of malaria vary across communities due to many different physical and social environmental factors. To identify those areas most suitable for malaria elimination or targeted control interventions, we used Bayesian models to estimate the spatiotemporal variation of malaria risk, rates, and trends to determine areas of high or low malaria burden compared to their geographical neighbours. We present a methodology using Bayesian hierarchical models with a Markov Chain Monte Carlo (MCMC) based inference to fit a generalised linear mixed model with a conditional autoregressive structure. We modelled clusters of similar spatiotemporal trends in malaria risk, using trend functions with constrained shapes and visualised high and low burden districts using a multi-criterion index derived by combining spatiotemporal risk, rates and trends of districts in Zambia. Our results indicate that over 3 million people in Zambia live in high-burden districts with either high mortality burden or high incidence burden coupled with an increasing trend over 16 years (2000 to 2015) for all age, under-five and over-five cohorts. Approximately 1.6 million people live in high-incidence burden areas alone. Using our method, we have developed a platform that can enable malaria programs in countries like Zambia to target those high-burden areas with intensive control measures while at the same time pursue malaria elimination efforts in all other areas. Our method enhances conventional approaches and measures to identify those districts which had higher rates and increasing trends and risk. This study provides a method and a means that can help policy makers evaluate intervention impact over time and adopt appropriate geographically targeted strategies that address the issues of both high-burden areas, through intensive control approaches, and low-burden areas, via specific elimination programs.

Incremental impact on malaria incidence following indoor residual spraying in a highly endemic area with high standard ITN access in Mozambique: results from a cluster-randomized study

Background

Attaining the goal of reducing the global malaria burden is threatened by recent setbacks in maintaining the effectiveness of vector control interventions partly due to the emergence of pyrethroid resistant vectors. One potential strategy to address these setbacks could be combining indoor residual spraying (IRS) with non-pyrethroids and standard insecticide-treated nets (ITNs). This study aimed to provide evidence on the incremental epidemiological benefit of using third-generation IRS product in a highly endemic area with high ITN ownership.

Methods

A cluster-randomized, open-label, parallel-arms, superiority trial was conducted in the Mopeia district in Zambezia, Mozambique from 2016 to 2018. The district had received mass distribution of alphacypermethrin ITNs two years before the trial and again mid-way. 86 clusters were defined, stratified and randomized to receive or not receive IRS with pirimiphos-methyl (Actellic®300 CS). Efficacy of adding IRS was assessed through malaria incidence in a cohort of children under five followed prospectively for two years, enhanced passive surveillance at health facilities and by community health workers, and yearly cross-sectional surveys at the peak of the transmission season.

Findings

A total of 1536 children were enrolled in the cohort. Children in the IRS arm experienced 4,801 cases (incidence rate of 3,532 per 10,000 children-month at risk) versus 5,758 cases in the no-IRS arm (incidence rate of 4,297 per 10,000 children-month at risk), resulting in a crude risk reduction of 18% and an incidence risk ratio of 0.82 (95% CI 0.79–0.86, p-value < 0.001). Facility and community passive surveillance showed a malaria incidence of 278 per 10,000 person-month in the IRS group (43,974 cases over 22 months) versus 358 (95% CI 355–360) per 10,000 person-month at risk in the no-IRS group (58,030 cases over 22 months), resulting in an incidence rate ratio of 0.65 (95% CI 0.60–0.71, p < 0.001). In the 2018 survey, prevalence in children under five in the IRS arm was significantly lower than in the no-IRS arm (OR 0.54, 95% CI, 0.31–0.92, p = 0.0241).

Conclusion

In a highly endemic area with high ITN access and emerging pyrethroid resistance, adding IRS with pirimiphos-methyl resulted in significant additional protection for children under five years of age.

Trial registration: ClinicalTrials.gov identifier NCT02910934, registered 22 September 2016, https://clinicaltrials.gov/ct2/show/NCT02910934?term=NCT02910934&draw=2&rank=1.

Quantifying and characterizing hourly human exposure to malaria vectors bites to address residual malaria transmission during dry and rainy seasons in rural Southwest Burkina Faso

Background

To sustain the efficacy of malaria vector control, the World Health Organization (WHO) recommends the combination of effective tools. Before designing and implementing additional strategies in any setting, it is critical to monitor or predict when and where transmission occurs. However, to date, very few studies have quantified the behavioural interactions between humans and Anopheles vectors in Africa. Here, we characterized residual transmission in a rural area of Burkina Faso where long lasting insecticidal nets (LLIN) are widely used.

Methods

We analysed data on both human and malaria vectors behaviours from 27 villages to measure hourly human exposure to vector bites in dry and rainy seasons using a mathematical model. We estimated the protective efficacy of LLINs and characterised where (indoors vs. outdoors) and when both LLIN users and non-users were exposed to vector bites.

Results

The percentage of the population who declared sleeping under a LLIN the previous night was very high regardless of the season, with an average LLIN use ranging from 92.43 to 99.89%. The use of LLIN provided > 80% protection against exposure to vector bites. The proportion of exposure for LLIN users was 29–57% after 05:00 and 0.05–12% before 20:00. More than 80% of exposure occurred indoors for LLIN users and the estimate reached 90% for children under 5 years old in the dry cold season.

Conclusions

LLINs are predicted to provide considerable protection against exposure to malaria vector bites in the rural area of Diébougou. Nevertheless, LLIN users are still exposed to vector bites which occurred mostly indoors in late morning. Therefore, complementary strategies targeting indoor biting vectors in combination with LLIN are expected to be the most efficient to control residual malaria transmission in this area.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-10304-y.

Which indoor residual spraying insecticide best complements standard pyrethroid long-lasting insecticidal nets for improved control of pyrethroid resistant malaria vectors?

Background

Where resources are available, non-pyrethroid IRS can be deployed to complement standard pyrethroid LLINs with the aim of achieving improved vector control and managing insecticide resistance. The impact of the combination may however depend on the type of IRS insecticide deployed. Studies comparing combinations of pyrethroid LLINs with different types of non-pyrethroid IRS products will be necessary for decision making.

Methods

The efficacy of combining a standard pyrethroid LLIN (DuraNet®) with IRS insecticides from three chemical classes (bendiocarb, chlorfenapyr and pirimiphos-methyl CS) was evaluated in an experimental hut trial against wild pyrethroid-resistant Anopheles gambiae s.l. in Cové, Benin. The combinations were also compared to each intervention alone. WHO cylinder and CDC bottle bioassays were performed to assess susceptibility of the local An. gambiae s.l. vector population at the Cové hut site to insecticides used in the combinations.

Results

Susceptibility bioassays revealed that the vector population at Cové, was resistant to pyrethroids (<20% mortality) but susceptible to carbamates, chlorfenapyr and organophosphates (≥98% mortality). Mortality of wild free-flying pyrethroid resistant An. gambiae s.l. entering the hut with the untreated net control (4%) did not differ significantly from DuraNet® alone (8%, p = 0.169). Pirimiphos-methyl CS IRS induced the highest mortality both on its own (85%) and in combination with DuraNet® (81%). Mortality with the DuraNet® + chlorfenapyr IRS combination was significantly higher than each intervention alone (46% vs. 33% and 8%, p<0.05) demonstrating an additive effect. The DuraNet® + bendiocarb IRS combination induced significantly lower mortality compared to the other combinations (32%, p<0.05). Blood-feeding inhibition was very low with the IRS treatments alone (3–5%) but increased significantly when they were combined with DuraNet® (61% - 71%, p<0.05). Blood-feeding rates in the combinations were similar to the net alone. Adding bendiocarb IRS to DuraNet® induced significantly lower levels of mosquito feeding compared to adding chlorfenapyr IRS (28% vs. 37%, p = 0.015).

Conclusions

Adding non-pyrethroid IRS to standard pyrethroid-only LLINs against a pyrethroid-resistant vector population which is susceptible to the IRS insecticide, can provide higher levels of vector mosquito control compared to the pyrethroid net alone or IRS alone. Adding pirimiphos-methyl CS IRS may provide substantial improvements in vector control while adding chlorfenapyr IRS can demonstrate an additive effect relative to both interventions alone. Adding bendiocarb IRS may show limited enhancements in vector control owing to its short residual effect.

Randomized trials of housing interventions to prevent malaria and Aedes-transmitted diseases: A systematic review and meta-analysis

BACKGROUND

Mosquito-borne diseases remain a significant public health problem in tropical regions. Housing improvements such as screening of doors and windows may be effective in reducing disease transmission, but the impact remains unclear.

OBJECTIVES

To examine whether housing interventions were effective in reducing mosquito densities in homes and the impact on the incidence of mosquito-borne diseases.

METHODS

In this systematic review and meta-analysis, we searched 16 online databases, including NIH PubMed, CINAHL Complete, LILACS, Ovid MEDLINE, and Cochrane Central Register of Controlled Trials for randomized trials published from database inception to June 30, 2020. The primary outcome was the incidence of any mosquito-borne diseases. Secondary outcomes encompassed entomological indicators of the disease transmission. I2 values were used to explore heterogeneity between studies. A random-effects meta-analysis was used to assess the primary and secondary outcomes, with sub-group analyses for type of interventions on home environment, study settings (rural, urban, or mixed), and overall house type (traditional or modern housing).

RESULTS

The literature search yielded 4,869 articles. After screening, 18 studies were included in the qualitative review, of which nine were included in the meta-analysis. The studies enrolled 7,200 households in Africa and South America, reporting on malaria or dengue only. The type of home environmental interventions included modification to ceilings and ribbons to close eaves, screening doors and windows with nets, insecticide-treated wall linings in homes, nettings over gables and eaves openings, mosquito trapping systems, metal-roofed houses with mosquito screening, gable windows and closed eaves, and prototype houses using southeast Asian designs. Pooled analysis depicted a lower risk of mosquito-borne diseases in the housing intervention group (OR = 0.68; 95% CI = 0.48 to 0.95; P = 0.03). Subgroup analysis depicted housing intervention reduced the risk of malaria in all settings (OR = 0.63; 95% CI = 0.39 to 1.01; P = 0.05). In urban environment, housing intervention was found to decrease the risk of both malaria and dengue infections (OR = 0.52; 95% CI = 0.27 to 0.99; P = 0.05).Meta-analysis of pooled odds ratio showed a significant benefit of improved housing in reducing indoor vector densities of both Aedes and Anopheles (OR = 0.35; 95% CI = 0.23 to 0.54; P<0.001).

CONCLUSIONS

Housing intervention could reduce transmission of malaria and dengue among people living in the homes. Future research should evaluate the protective effect of specific house features and housing improvements associated with urban development.

Non-adherence to long-lasting insecticide treated bednet use following successful malaria control in Tororo, Uganda

Indoor residual spraying (IRS) and long-lasting insecticide-treated bednets (LLINs) are common tools for reducing malaria transmission. We studied a cohort in Uganda with universal access to LLINs after 5 years of sustained IRS to explore LLIN adherence when malaria transmission has been greatly reduced. Eighty households and 526 individuals in Nagongera, Uganda were followed from October 2017 -October 2019. Every two weeks, mosquitoes were collected from sleeping rooms and LLIN adherence the prior night assessed. Episodes of malaria were diagnosed using passive surveillance. Risk factors for LLIN non-adherence were evaluated using multi-level mixed logistic regression. An age-matched case-control design was used to measure the association between LLIN non-adherence and malaria. Across all time periods, and particularly in the last 6 months, non-adherence was higher among both children <5 years (OR 3.31, 95% CI: 2.30-4.75; p<0.001) and school-aged children 5-17 years (OR 6.88, 95% CI: 5.01-9.45; p<0.001) compared to adults. In the first 18 months, collection of fewer mosquitoes was associated with non-adherence (OR 3.25, 95% CI: 2.92-3.63; p<0.001), and, in the last 6 months, residents of poorer households were less adherent (OR 5.1, 95% CI: 1.17-22.2; p = 0.03). Any reported non-adherence over the prior two months was associated with a 15-fold increase in the odds of having malaria (OR 15.0, 95% CI: 1.95 to 114.9; p = 0.009). Knowledge about LLIN use was high, and the most frequently reported barriers to use included heat and low perceived risk of malaria. Children, particularly school-aged, participants exposed to fewer mosquitoes, and those from poorer households, were less likely to use LLINs. Non-adherence to LLINs was associated with an increased risk of malaria. Strategies, such as behavior change communications, should be prioritized to ensure consistent LLIN use even when malaria transmission has been greatly reduced.

Estimating malaria chemoprevention and vector control coverage using program and campaign data: A scoping review of current practices and opportunities

BACKGROUND

Accurate estimation of intervention coverage is a vital component of malaria program monitoring and evaluation, both for process evaluation (how well program targets are achieved), and impact evaluation (whether intervention coverage had an impact on malaria burden). There is growing interest in maximizing the utility of program data to generate interim estimates of intervention coverage in the periods between large-scale cross-sectional surveys (the gold standard). As such, this study aimed to identify relevant concepts and themes that may guide future optimization of intervention coverage estimation using routinely collected data, or data collected during and following intervention campaigns, with a particular focus on strategies to define the denominator.

METHODS

We conducted a scoping review of current practices to estimate malaria intervention coverage for insecticide-treated nets (ITNs); indoor residual spray (IRS); intermittent preventive treatment in pregnancy (IPTp); mass drug administration (MDA); and seasonal malaria chemoprevention (SMC) interventions; case management was excluded. Multiple databases were searched for relevant articles published from January 1, 2015 to June 1, 2018. Additionally, we identified and included other guidance relevant to estimating population denominators, with a focus on innovative techniques.

RESULTS

While program data have the potential to provide intervention coverage data, there are still substantial challenges in selecting appropriate denominators. The review identified a lack of consistency in how coverage was defined and reported for each intervention type, with denominator estimation methods not clearly or consistently reported, and denominator estimates rarely triangulated with other data sources to present the feasible range of denominator values and consequently the range of likely coverage estimates.

CONCLUSIONS

Though household survey-based estimates of intervention coverage remain the gold standard, efforts should be made to further standardize practices for generating interim measurements of intervention coverage from program data, and for estimating and reporting population denominators. This includes fully describing any projections or adjustments made to existing census or population data, exploring opportunities to validate available data by comparing with other sources, and explaining how the denominator has been restricted (or not) to reflect exclusion criteria.

The Impact of Multiple Rounds of Indoor Residual Spraying on Malaria Incidence and Hemoglobin Levels in a High-Transmission Setting

BACKGROUND

Indoor residual spraying (IRS) is widely used as a vector control measure, although there are conflicting findings of its effectiveness in reducing malaria incidence. The objective of this study was to estimate the effect of multiple IRS rounds on malaria incidence and hemoglobin levels in a cohort of children in rural southeastern Uganda.

METHODS

The study was based upon a dynamic cohort of children aged 0.5-10 years enrolled from August 2011 to June 2017 in Nagongera Subcounty. Confirmed malaria infections and hemoglobin levels were recorded over time for each participant. After each of 4 rounds of IRS, malaria incidence, hemoglobin levels, and parasite density were evaluated and compared with pre-IRS levels. Analyses were carried out at the participant level while accounting for repeated measures and clustering by household.

RESULTS

Incidence rate ratios comparing post-IRS to pre-IRS incidence rates for age groups 0-3, 3-5, and 5-11 were 0.108 (95% confidence interval [CI], .078-.149), 0.173 (95% CI, .136-.222), and 0.226 (95% CI, .187-.274), respectively. The mean hemoglobin levels significantly increased from 11.01 (pre-IRS) to 12.18 g/dL (post-IRS).

CONCLUSIONS

Our study supports the policy recommendation of IRS usage in a stable and perennial transmission area to rapidly reduce malaria transmission.

Adaptive interventions for optimizing malaria control: an implementation study protocol for a block-cluster randomized, sequential multiple assignment trial

BACKGROUND

In the past two decades, the massive scale-up of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) has led to significant reductions in malaria mortality and morbidity. Nonetheless, the malaria burden remains high, and a dozen countries in Africa show a trend of increasing malaria incidence over the past several years. This underscores the need to improve the effectiveness of interventions by optimizing first-line intervention tools and integrating newly approved products into control programs. Because transmission settings and vector ecologies vary from place to place, malaria interventions should be adapted and readapted over time in response to evolving malaria risks. An adaptive approach based on local malaria epidemiology and vector ecology may lead to significant reductions in malaria incidence and transmission risk.

METHODS/DESIGN

This study will use a longitudinal block-cluster sequential multiple assignment randomized trial (SMART) design with longitudinal outcome measures for a period of 3 years to develop an adaptive intervention for malaria control in western Kenya, the first adaptive trial for malaria control. The primary outcome is clinical malaria incidence rate. This will be a two-stage trial with 36 clusters for the initial trial. At the beginning of stage 1, all clusters will be randomized with equal probability to either LLIN, piperonyl butoxide-treated LLIN (PBO Nets), or LLIN + IRS by block randomization based on their respective malaria risks. Intervention effectiveness will be evaluated with 12 months of follow-up monitoring. At the end of the 12-month follow-up, clusters will be assessed for "response" versus "non-response" to PBO Nets or LLIN + IRS based on the change in clinical malaria incidence rate and a pre-defined threshold value of cost-effectiveness set by the Ministry of Health. At the beginning of stage 2, if an intervention was effective in stage 1, then the intervention will be continued. Non-responders to stage 1 PBO Net treatment will be randomized equally to either PBO Nets + LSM (larval source management) or an intervention determined by an enhanced reinforcement learning method. Similarly, non-responders to stage 1 LLIN + IRS treatment will be randomized equally to either LLIN + IRS + LSM or PBO Nets + IRS. There will be an 18-month evaluation follow-up period for stage 2 interventions. We will monitor indoor and outdoor vector abundance using light traps. Clinical malaria will be monitored through active case surveillance. Cost-effectiveness of the interventions will be assessed using Q-learning.

DISCUSSION

This novel adaptive intervention strategy will optimize existing malaria vector control tools while allowing for the integration of new control products and approaches in the future to find the most cost-effective malaria control strategies in different settings. Given the urgent global need for optimization of malaria control tools, this study can have far-reaching implications for malaria control and elimination.

TRIAL REGISTRATION

US National Institutes of Health, study ID NCT04182126 . Registered on 26 November 2019.

The Impact of Control Interventions on Malaria Burden in Young Children in a Historically High-Transmission District of Uganda: A Pooled Analysis of Cohort Studies from 2007 to 2018

There is limited evidence on whether malaria elimination is feasible in high-transmission areas of Africa. Between 2007 and 2018, we measured the impact of malaria control interventions in young children enrolled in three clinical trials and two observational studies in Tororo, Uganda, a historically high-transmission area. Data were pooled from children aged 0.5–2 years. Interventions included individually assigned chemoprevention and repeated rounds of indoor residual spraying (IRS) of insecticide. All children received long-lasting insecticidal nets (LLINs) and treatment for symptomatic malaria with artemisinin-based combination therapy. Malaria incidence was measured using passive surveillance and parasite prevalence by microscopy and molecular methods at regular intervals. Poisson’s generalized linear mixed-effects models were used to estimate the impact of various control interventions. In total, 939 children were followed over 1,221.7 person years. In the absence of chemoprevention and IRS (reference group), malaria incidence was 4.94 episodes per person year and parasite prevalence 47.3%. Compared with the reference group, implementation of IRS was associated with a 97.6% decrease (95% CI: 93.3–99.1%, P = 0.001) in the incidence of malaria and a 96.0% decrease (95% CI: 91.3–98.2%, P < 0.001) in parasite prevalence (both measured after the fifth and sixth rounds of IRS). The addition of chemoprevention with monthly dihydroartemisinin–piperaquine to IRS was associated with a 99.5% decrease (95% CI: 98.6–99.9%, P < 0.001) in the incidence of malaria. In a historically high–malaria burden area of Uganda, a combination of LLINs, effective case management, IRS, and chemoprevention was associated with almost complete elimination of malaria in young children.

Drinking water and sanitation conditions are associated with the risk of malaria among children under five years old in sub-Saharan Africa: A logistic regression model analysis of national survey data

Current efforts for the prevention of malaria have resulted in notable reductions in the global malaria burden; however, they are not enough. Good hygiene is universally considered one of the most efficacious and straightforward measures to prevent disease transmission. This work analyzed whether improved drinking water and sanitation (WS) conditions were associated with a decreased risk of malaria infection. Data were acquired through surveys published between 2006 and 2018 from the Demographic and Health Program in sub-Saharan Africa (SSA). Multiple logistic regression was used for each national survey to identify the associations between WS conditions and malaria infection diagnosed by microscopy or a malaria rapid diagnostic test (RDT) among children (0-59 months), with adjustments for age, gender, indoor residual spraying (IRS), insecticide-treated net (ITN) use, house quality, and the mother's highest educational level. Individual nationally representative survey odds ratios (ORs) were combined to obtain a summary OR using a random-effects meta-analysis. Among the 247,440 included children, 18.8% and 24.2% were positive for malaria infection based on microscopy and RDT results, respectively. Across all surveys, both unprotected water and no facility users were associated with increased malaria risks (unprotected water: aOR 1.17, 95% CI 1.07-1.27, P = 0.001; no facilities: aOR 1.35, 95% CI 1.24-1.47, P < 0.001; respectively), according to microscopy, whereas the odds of malaria infection were 48% and 49% less among piped water and flush-toilet users, respectively (piped water: aOR 0.52, 95% CI 0.45-0.59, P < 0.001; flush toilets: aOR 0.51, 95% CI 0.43-0.61, P < 0.001). The trends of individuals diagnosed by RDT were consistent with those of individuals diagnosed by microscopy. Risk associations were more pronounced among children with a "nonpoor" socioeconomic status who were unprotected water or no facility users. WS conditions are a vital risk factor for malarial infection among children (0-59 months) across SSA. Improved WS conditions should be considered a potential intervention for the prevention of malaria in the long term.

Improving the performance of spray operators through monitoring and evaluation of insecticide concentrations of pirimiphos-methyl during indoor residual spraying for malaria control on Bioko Island

Background

Quality control of indoor residual spraying (IRS) is necessary to ensure that spray operators (SOs) deposit the correct concentration of insecticide on sprayed structures, while also confirming that spray records are not being falsified.

Methods

Using high-performance liquid chromatography (HPLC), this study conducted quality control of the organophosphate insecticide pirimiphos-methyl (Actellic 300CS), during the 2018 IRS round on Bioko Island, Equatorial Guinea. Approximately 60 SOs sprayed a total of 67,721 structures in 16,653 houses during the round. Houses that were reportedly sprayed were randomly selected for quality control testing. The SOs were monitored twice in 2018, an initial screening in March followed by sharing of results with the IRS management team and identification of SOs to be re-trained, and a second screening in June to monitor the effectiveness of training. Insecticide samples were adhesive-lifted from wooden and cement structures and analysed using HPLC.

Results

The study suggests that with adequate quality control measures and refresher training, suboptimal spraying was curtailed, with a significant increased concentration delivered to the bedroom (difference = 0.36, P < 0.001) and wooden surfaces (difference 0.41, P = 0.001). Additionally, an increase in effective coverage by SOs was observed, improving from 80.7% in March to 94.7% in June after re-training (McNemar’s test; P = 0.03).

Conclusions

The ability to randomly select, locate, and test houses reportedly sprayed within a week via HPLC has led to improvements in the performance of SOs on Bioko Island, enabling the project to better evaluate its own performance.

Upsurge of malaria transmission after indoor residual spraying withdrawal in Atacora region in Benin, West Africa

Background

In Benin, malaria vector control mostly relies on long-lasting, insecticidal-treated bed nets (LLINs) and indoor residual spraying (IRS) operations. From 2011 to 2016, an IRS programme has been implemented in Atacora region. However, in 2017 the programme was withdrawn from two other regions in the northern part of the country, with hopes that gains would be relatively sustained because of the seasonality of malaria transmission. What would be the vulnerability of populations to malaria after the withdrawal of IRS?

Methods

Monthly mosquito collections were performed through human landing captures (HLCs) for 24 months (from January to December 2016 during the last IRS campaign, and from January to December 2018, 2 years after the withdrawal of IRS). Vector mosquitoes biting density was sampled by HLC and was tested for presence of Plasmodium falciparum sporozoites. The carcass of these mosquitoes (abdomens, wing, legs) were subjected to molecular species identification using polymerase chain reaction (PCR) assays.

Results

It is noticed a drastic increase (~ 3 times higher) of vector abundance after the withdrawal of IRS. Mosquito biting rates in the 3 survey districts increased significantly after IRS was withdrawn. In 2018, after IRS cessation a significant increase of entomological inoculation rate was recorded, where each inhabitant received an average of 94.9 infected bites/year to 129.21 infected bites/year against an average of 17.15 infected bites/year to 24.82 infected bites/year in 2016.

Conclusion

It is obvious that the withdrawal of IRS confers a vulnerability of the population with regard to the malaria transmission. Robust monitoring is needed to better understand when and where IRS should be most adequate, or can be safely withdrawn. In case of withdrawal, adapted accompanying measures should be proposed according to the context not only to maintain the gains capitalized with IRS, but also to avoid any rebound of transmission.

Medical reversals in low- and middle-income countries

BACKGROUND

Low- to middle-income countries (LMICs) often have limited budgets for health care, and as such, they need to prioritize health care interventions that are evidence based. However, sometimes, interventions are implemented despite a lack of supporting evidence because of a perceived biologic plausibility or because they have worked in other populations. Later, some of these interventions are shown to either lack benefit or are harmful in randomized studies, which we call a medical reversal.

MAIN BODY

In this paper, we discuss a variety of medical reversals in LMICs, ranging from tuberculosis to nutrition to malaria to septic shock. These practices were previously identified, but we wish to highlight those that are most relevant to LMICs.

CONCLUSION

Identifying and eliminating these practices will help in better allocation of limited health care resources and dollars in LMICs.

Status of insecticide resistance in Anopheles gambiae (s.l.) of The Gambia

Background

Vector control activities, namely long-lasting insecticidal nets (LLIN) and indoor residual spraying (IRS), have contributed significantly to the decreasing malaria burden observed in The Gambia since 2008. Nevertheless, insecticide resistance may threaten such success; it is important to regularly assess the susceptibility of local malaria vectors to available insecticides.

Methods

In the transmission seasons of 2016 and 2017, Anopheles gambiae (s.l.) larvae were sampled in or around the nine vector surveillance sentinel sites of the Gambia National Malaria Control Programme (GNMCP) and in a few additional sampling points. Using WHO susceptibility bioassays, female adult mosquitoes were exposed to insecticide-impregnated papers. Molecular identification of sibling species and insecticide resistance molecular markers was done on a subset of 2000 female mosquitoes.

Results

A total of 4666 wild-caught female adult mosquitoes were exposed to either permethrin (n = 665), deltamethrin (n = 744), DDT (n = 1021), bendiocarb (n = 990) or pirimiphos-methyl (n = 630) insecticide-impregnated papers and control papers (n = 616). Among the 2000 anophelines, 1511 (80.7%) were Anopheles arabiensis, 204 (10.9%) Anopheles coluzzii, 75 (4%) Anopheles gambiae (s.s.), and 83 (4.4%) An. gambiae (s.s.) and An. coluzzii hybrids. There was a significant variation in the composition and species distribution by regions and year, P = 0.009. Deltamethrin, permethrin and DDT resistance was found in An. arabiensis, especially in the coastal region, and was mediated by Vgsc-1014F/S mutations (odds ratio = 34, P = 0.014). There was suspected resistance to pirimiphos-methyl (actellic 300CS) in the North Bank Region although only one survivor had the Ace-1-119S mutation.

Conclusions

As no confirmed resistance to bendiocarb and actellic 300CS was detected, the national malaria control programme can continue using these insecticides for IRS. Nevertheless, the detection of Ace-1 119S mutation warrants extensive monitoring. The source of insecticide pressure driving insecticide resistance to pyrethroids and DDT detected at the coastal region should be further investigated in order to properly manage the spread of resistance in The Gambia.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3538-0) contains supplementary material, which is available to authorized users.

Impact of combining indoor residual spraying and long-lasting insecticidal nets on Anopheles arabiensis in Ethiopia: results from a cluster randomized controlled trial

BACKGROUND

Indoor residual house spraying (IRS) and long-lasting insecticidal nets (LLINs) are the key front-line malaria vector interventions against Anopheles arabiensis, the sole primary malaria vector in Ethiopia. Universal coverage of both interventions has been promoted and there is a growing demand in combinations of interventions for malaria control and elimination. This study compared the impact on entomological outcomes of combining IRS and LLINs with either intervention alone in Adami Tullu district, south-central Ethiopia. The epidemiological outcomes were recently published on a separate paper.

METHODS

This factorial, cluster-randomized, controlled trial randomized villages to four study arms: IRS + LLIN, IRS, LLIN, and control. LLINs (PermaNet 2.0) were provided free of charge. IRS with propoxur was applied before the main malaria transmission season in 2014, 2015 and 2016. Adult mosquitoes were collected in randomly selected villages in each arm using CDC light trap catch (LTC) set close to a sleeping person, pyrethrum spray catch (PSC), and artificial pit shelter (PIT), for measuring mosquito host-seeking density (HSD), indoor resting density (IRD), and outdoor resting density (ORD), respectively. Human landing catch (HLC) was performed in a sub-set of villages to monitor An. arabiensis human biting rates (HBR). Mean vector densities and HBR were compared among study arms using incidence rate ratio (IRR) calculated by negative binomial regression.

RESULTS

There were no significant differences in mean densities (HSD, IRD, ORD) and HBR of An. arabiensis between the IRS + LLIN arm and the IRS arm (p > 0.05). However, mean HSD, IRD, ORD, and HBR were significantly lower in the IRS + LLIN arm than in the LLIN alone arm (p < 0.05). All An. arabiensis tested for malaria infection were negative for Plasmodium species. For this reason, the entomological inoculation rate could not be determined.

CONCLUSIONS

The IRS + LLIN were as effective as IRS alone in reducing densities and HBR of An. arabiensis. However, the effectiveness of the two interventions combined was higher than LLINs alone in reducing densities and HBR of the vector. Added impact of the combination intervention against malaria infectivity rates of An. arabiensis compared to either intervention alone remains unknown and warrants further research. Trial registration PACTR201411000882128. Registered 8 September 2014, https://trialsjournal.biomedcentral.com/articles/10.1186/s13063-016-1154-2.

Reduced mosquito survival in metal-roof houses may contribute to a decline in malaria transmission in sub-Saharan Africa

In The Gambia, metal-roof houses were hotter during the day than thatched-roof houses. After 24 h, the mortality of Anopheles gambiae, the principal African malaria vector, was 38% higher in metal-roof houses than thatched ones. During the day, mosquitoes in metal-roof houses moved from the hot roof to cooler places near the floor, where the temperature was still high, reaching 35 °C. In laboratory studies, at 35 °C few mosquitoes survived 10 days, the minimum period required for malaria parasite development. Analysis of epidemiological data showed there was less malaria and lower vector survival rates in Gambian villages with a higher proportion of metal roofs. Our findings are consistent with the hypothesis that the indoor climate of metal-roof houses, with higher temperatures and lower humidity, reduces survivorship of indoor-resting mosquitoes and may have contributed to the observed reduction in malaria burden in parts of sub-Saharan Africa.

Indoor residual spraying for preventing malaria in communities using insecticide-treated nets

BACKGROUND

Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) are used to control malaria vectors. Both strategies use insecticides to kill mosquitoes that bite and rest indoors. For ITNs, the World Health Organization (WHO) only recommended pyrethroids until 2018, but mosquito vectors are becoming resistant to this insecticide. For IRS, a range of insecticides are recommended. Adding IRS to ITNs may improve control, simply because two interventions may be better than one; it may improve malaria control where ITNs are failing due to pyrethroid resistance; and it may slow the emergence and spread of pyrethroid resistance.

OBJECTIVES

To summarize the effect on malaria of additionally implementing IRS, using non-pyrethroid-like or pyrethroid-like insecticides, in communities currently using ITNs.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; Embase; LILACS; the WHO International Clinical Trials Registry Platform; ClinicalTrials.gov; and the ISRCTN registry up to 18 March 2019.

SELECTION CRITERIA

Cluster-randomized controlled trials (cRCTs), interrupted time series (ITS), or controlled before-and-after studies (CBAs) comparing IRS plus ITNs with ITNs alone.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for eligibility, analyzed risk of bias, and extracted data. We used risk ratio (RR) and 95% confidence intervals (CI). We stratified by type of insecticide: 'non-pyrethroid-like', as this could improve malaria control better than adding IRS insecticides that have the same way of working as the insecticide on ITNs ('pyrethroid-like'). We used subgroup analysis of ITN usage in the trials to explore heterogeneity. We assessed the certainty of evidence using the GRADE approach.

MAIN RESULTS

Six cRCTs (eight comparisons) met our inclusion criteria conducted since 2008 in sub-Saharan Africa. Malaria transmission in all sites was from mosquitoes belonging to the Anopheles gambiae s.l. complex species; two trials in Benin and Tanzania also reported the vector Anopheles funestus. Three trials used insecticide with targets different to pyrethroids (two used bendiocarb and one used pirimiphos-methyl); two trials used dichloro-diphenyl-trichlorethane (DDT), an insecticide with the same target as pyrethroids; and one trial used both types of insecticide (pyrethroid deltamethrin in the first year, switching to bendiocarb for the second-year). ITN usage was greater than 50% in three trials, and less than 50% in the remainder.Indoor residual spraying using 'non-pyrethroid-like' insecticides Adding IRS with a non-pyrethroid-like insecticide had mixed results. Overall, we do not know if the addition of IRS impacted on malaria incidence (rate ratio 0.93, 95% CI 0.46 to 1.86; 2 cRCTs, 566 child-years; very low-certainty evidence); it may have reduced malaria parasite prevalence (0.67, 95% CI 0.35 to 1.28; 5 comparisons from 4 cRCTs, 10,440 participants; low-certainty evidence); and it may have reduced the prevalence of anaemia (RR CI 0.46, 95% 0.18 to 1.20; 3 comparisons from 2 cRCTs, 2026 participants; low-certainty evidence). Three trials reported the impact on EIR, with variable results; overall, we do not know if IRS had any effect on the EIR in communities using ITNs (very low-certainty evidence). Trials also reported the adult mosquito density and the sporozoite rate, but we could not summarize or pool these entomological outcomes due to unreported data. ITN usage did not explain the variation in malaria outcomes between different studies. One trial reported no effect on malaria incidence or parasite prevalence in the first year, when the insecticide used for IRS had the same target as pyrethroids, but showed an effect on both outcomes in the second year, when the insecticide was replaced by one with a different target.Two trials measured the prevalence of pyrethroid resistance before and after IRS being introduced: no difference was detected, but these data are limited.Indoor residual spraying using 'pyrethroid-like' insecticidesAdding IRS using a pyrethroid-like insecticide did not appear to markedly alter malaria incidence (rate ratio 1.07, 95% CI 0.80 to 1.43; 2 cRCTs, 15,717 child-years; moderate-certainty evidence), parasite prevalence (RR 1.11, 95% CI 0.86 to 1.44; 3 cRCTs, 10,820 participants; moderate-certainty evidence), or anaemia prevalence (RR 1.12, 95% CI 0.89 to 1.40; 1 cRCT, 4186 participants; low-certainty evidence). Data on the entomological inoculation rate (EIR) were limited, and therefore we do not know if IRS had any effect on the EIR in communities using ITNs (very low-certainty evidence).

AUTHORS' CONCLUSIONS

Four trials have evaluated adding IRS using 'non-pyrethroid-like' insecticides in communities using ITNs. Some of these trials showed effects, and others did not. Three trials have evaluated adding IRS using 'pyrethroid-like' insecticides in communities using ITNs, and these studies did not detect an additional effect of the IRS. Given the wide geographical variety of malaria endemicities, transmission patterns, and insecticide resistance, we need to be cautious with inferences to policy from the limited number of trials conducted to date, and to develop relevant further research to inform decisions.

Long-lasting insecticidal nets and indoor residual spraying may not be sufficient to eliminate malaria in a low malaria incidence area: results from a cluster randomized controlled trial in Ethiopia

Background

Conflicting results exist on the added benefit of combining long-lasting insecticidal nets (LLINs) with indoor residual spraying (IRS) to control malaria infection. The main study objective was to evaluate whether the combined use of LLINs and IRS with propoxur provides additional protection against Plasmodium falciparum and/or Plasmodium vivax among all age groups compared to LLINs or IRS alone.

Methods

This cluster-randomized, controlled trial was conducted in the Rift Valley area of Ethiopia from September 2014 to January 2017 (121 weeks); 44 villages were allocated to each of four study arms: LLIN + IRS, IRS, LLIN, and control. Each week, 6071 households with 34,548 persons were surveyed by active and passive case detection for clinical malaria. Primary endpoints were the incidence of clinical malaria and anaemia prevalence.

Results

During the study, 1183 malaria episodes were identified, of which 55.1% were P. falciparum and 25.3% were P. vivax, and 19.6% were mixed infections of P. falciparum and P. vivax. The overall malaria incidence was 16.5 per 1000 person-years of observation time (PYO), and similar in the four arms with 17.2 per 1000 PYO in the LLIN + IRS arm, 16.1 in LLIN, 17.0 in IRS, and 15.6 in the control arm. There was no significant difference in risk of anaemia among the trial arms.

Conclusions

The clinical malaria incidence and anaemia prevalence were similar in the four study groups. In areas with low malaria incidence, using LLINs and IRS in combination or alone may not eliminate malaria. Complementary interventions that reduce residual malaria transmission should be explored in addition to LLINs and IRS to further reduce malaria transmission in such settings.

Trial registration PACTR201411000882128 (08 September 2014)

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2775-1) contains supplementary material, which is available to authorized users.

Indoor residual spray bio-efficacy and residual activity of a clothianidin-based formulation (SumiShield® 50WG) provides long persistence on various wall surfaces for malaria control in the Democratic Republic of the Congo

BACKGROUND

Bio-efficacy and residual activity of SumiShield® 50WG (50%, w/w) with active ingredient clothianidin, a neonicotinoid compound, was assessed using an insecticide-susceptible laboratory strain of Anopheles arabiensis. Implications of the findings are examined in the context of potential alternative insecticides for indoor residual spraying in Lualaba Province, Democratic Republic of the Congo.

METHODS

Contact surface bioassays were conducted for 48 weeks on four types of walls (unbaked clay, baked clay, cement, painted cement) in simulated semi-field experimental conditions using two different doses of clothianidin active ingredient (200 mg ai/sq m and 300 mg ai/sq m). Additionally, two types of walls (painted cement and baked clay) were examined in occupied houses using the 300-mg dosage. Laboratory-reared An. arabiensis were exposed to treated surfaces or untreated (controls) for 30 min. Mortality was recorded at 24-h intervals for 120 h.

RESULTS

Under semi-field experimental conditions, there was no significant difference in mortality over time between the two doses of clothianidin. The mortality rates remained above 60% up to 48 weeks on all four wall surface types. The formulation performed better on cement and unbaked clay with a mean final mortality rate above 90%. Under natural conditions, there was no significant difference in response between baked clay and painted cement walls with a mean final mortality rate above 90%. The insecticide also performed significantly better in natural settings compared to semi-field experimental conditions.

CONCLUSION

Depending on the type of experimental surface, the residual activity of the two doses of clothianidin was between 28 and 48 weeks based on a 60% mortality endpoint. Clothianidin at 300 mg ai/sq m applied on two house walls (baked clay or painted cement) performed equally well (> 80% mortality) on both surfaces up to week 41 (approximately 9.5 months). Extended bioassay holding periods (up to 120 h) may present with excess natural mortality in the untreated controls, thus complicating analysis.

Cost-effectiveness of a combined intervention of long lasting insecticidal nets and indoor residual spraying compared with each intervention alone for malaria prevention in Ethiopia

Background

The effectiveness of long lasting insecticidal nets (LLINs) and indoor residual spraying (IRS), for malaria prevention, have been established in several studies. However, the available evidence about the additional resources required for a combined implementation (LLIN + IRS) with respect to the added protection afforded is limited. Therefore, the aim of this study was to compare the cost-effectiveness of combined implementation of LLINs and IRS, compared with LLINs alone, IRS alone, and routine practice in Ethiopia.

Methods

The study was performed alongside a cluster randomized controlled trial of malaria prevention conducted in Adami Tullu district, in Ethiopia, from 2014 to 2016. In addition, literature-based cost-effectiveness analysis—using effectiveness information from a systematic review of published articles was conducted. Costing of the interventions were done from the providers’ perspective. The health-effect was measured using disability adjusted life years (DALYs) averted, and combined with cost information using a Markov life-cycle model. In the base-case analysis, health-effects were based on the current trial, and in addition, a scenario analysis was performed based on a literature survey.

Results

The current trial-based analysis showed that routine practice is not less effective and therefore dominates both the combined intervention and singleton intervention due to lower costs. The literature-based analysis had shown that combined intervention had an incremental cost-effectiveness ratio of USD 1403 per DALY averted, and USD 207 per DALY averted was estimated for LLIN alone. In order for the ICER for the combined intervention to be within a range of 1 GDP per capita per DALY averted, the annual malaria incidence in the area should be at least 13%, and the protective-effectiveness of combined implementation should be at least 53%.

Conclusions

Based on the current trial-based analysis, LLINs and IRS are not cost-effective compared to routine practice. However, based on the literature-based analysis, LLIN alone is likely to be cost-effective compared to 3 times GDP per capita per DALY averted. The annual malaria probability and protective-effectiveness of combined intervention are key determinants of the cost-effectiveness of the interventions.

Trial registration PACTR201411000882128 (Registered 8 September 2014). http://www.pactr.org/ATMWeb/appmanager/atm/atmregistry?dar=true&tNo=PACTR201411000882128

Incidence and Outcomes after Out-of-Hospital Medical Emergencies in Gambia: A Case for the Integration of Prehospital Care and Emergency Medical Services in Primary Health Care

BACKGROUND

The Gambia is going through a rapid epidemiologic transition with a dual disease burden of infections and non-communicable diseases occurring at the same time. Acute, time-sensitive, medical emergencies such as trauma, obstetric emergencies, respiratory failure, and stroke are leading causes of morbidity and mortality among adults in the country.ProblemData on medical emergency care and outcomes are lacking in The Gambia. Data on self-reported medical emergencies among adults in a selection of Gambian communities are presented in this report.

METHODS

A total of 320 individuals were surveyed from 34 communities in the greater Banjul area of The Gambia using a survey instrument estimating the incidence of acute medical emergencies in an adult population. Self-reported travel time to a health facility during medical emergencies and patterns of health-seeking behavior with regard to type of facility visited and barriers to accessing emergency care, including cost and medical insurance coverage, are presented in this report.

RESULTS

Of the 320 individuals surveyed, 262 agreed to participate resulting in a response rate of 82%. Fifty-two percent of respondents reported an acute medical emergency in the preceding year that required urgent evaluation at a health facility. The most common facility visited during such emergencies was a health center. Eighty-seven percent of respondents reported a travel time of less than one hour during medical emergencies. Out-of-pocket cost of medications accounted for the highest expenditure during emergencies. There was a low awareness and willingness to subscribe to health insurance among individuals surveyed.

CONCLUSION

There is a high incidence of acute medical emergencies among adults in The Gambia which are associated with adverse outcomes due to a combination of poor health literacy, high out-of-pocket expenditures on medications, and poor access to timely prehospital emergency care. There is an urgent need to develop prehospital acute care and Emergency Medical Services (EMS) in the primary health sector as part of a strategy to reduce mortality and morbidity in the country. TourayS, SanyangB, ZandrowG, TourayI. Incidence and outcomes after out-of-hospital medical emergencies in Gambia: a case for the integration of prehospital care and Emergency Medical Services in primary health care. Prehosp Disaster Med. 2018;33(6):650-657.

Cluster-randomized trial of monthly malaria prophylaxis versus focused screening and treatment: a study protocol to define malaria elimination strategies in Cambodia

BACKGROUND

Malaria remains a critical public health problem in Southeast Asia despite intensive containment efforts. The continued spread of multi-drug-resistant Plasmodium falciparum has led to calls for malaria elimination on the Thai-Cambodian border. However, the optimal approach to elimination in difficult-to-reach border populations, such as the Military, remains unclear.

METHODS/DESIGN

A two-arm, cluster-randomized controlled, open-label pilot study is being conducted in military personnel and their families at focal endemic areas on the Thai-Cambodian border. The primary objective is to compare the effectiveness of monthly malaria prophylaxis (MMP) with dihydroartemisinin-piperaquine and weekly primaquine for 12 weeks compared with focused screening and treating (FSAT) following current Cambodian national treatment guidelines. Eight separate military encampments, making up approximately 1000 military personnel and their families, undergo randomization to the MMP or FSAT intervention for 3 months, with an additional 3 months' follow-up. In addition, each treatment cluster of military personnel and civilians is also randomly assigned to receive either permethrin- or sham (water)-treated clothing in single-blind fashion. The primary endpoint is risk reduction for malaria infection in geographically distinct military encampments based on their treatment strategy. Monthly malaria screening in both arms is done via microscopy, PCR, and rapid diagnostic testing to compare both the accuracy and cost-effectiveness of diagnostic modalities to detect asymptomatic infection. Universal glucose-6-phosphate dehydrogenase (G6PD) deficiency screening is done at entry, comparing the results from a commercially available rapid diagnostic test, the fluorescence spot test, and quantitative testing for accuracy and cost-effectiveness. The comparative safety of the interventions chosen is also being evaluated.

DISCUSSION

Despite the apparent urgency, the key operational elements of proposed malaria elimination strategies in Southeast Asian mobile and migrant populations, including the Military, have yet to be rigorously tested in a well-controlled clinical study. Here, we present a protocol for the primary evaluation of two treatment paradigms - monthly malaria prophylaxis and focused screening and treatment - to achieve malaria elimination in a Cambodian military population. We will also assess the feasibility and incremental benefit of outdoor-biting vector intervention - permethrin-treated clothing. In the process, we aim to define the cost-effectiveness of the inputs required for success including a responsive information system, skilled human resource and laboratory infrastructure requirements, and quality management. Despite being a relatively low transmission area, the complexities of multi-drug-resistant malaria and the movement of vulnerable populations require an approach that is not only technically sound, but simple enough to be achievable.

TRIAL REGISTRATION

ClinicalTrials.gov, ID: NCT02653898 . Registered on 13 January 2016.

Is chronic malnutrition associated with an increase in malaria incidence? A cohort study in children aged under 5 years in rural Gambia

Background

Malnutrition is common in children in sub-Saharan Africa and is thought to increase the risk of infectious diseases, including malaria. The relationship between malnutrition and malaria was examined in a cohort of 6–59 month-old children in rural Gambia, in an area of seasonal malaria transmission. The study used data from a clinical trial in which a cohort of children was established and followed for clinical malaria during the 2011 transmission season. A cross-sectional survey to determine the prevalence of malaria and anaemia, and measure the height and weight of these children was carried out at the beginning and end of the transmission season. Standard anthropometric indices (stunting, wasting and underweight) were calculated using z-scores.

Results

At the beginning of the transmission season, 31.7% of children were stunted, 10.8% wasted and 24.8% underweight. Stunting was more common in Fula children than other ethnicities and in children from traditionally constructed houses compared to more modern houses. Stunted children and underweight children were significantly more likely to have mild or moderate anaemia. During the transmission season, 13.7% of children had at least one episode of clinical malaria. There was no association between stunting and malaria incidence (odds ratio = 0.79, 95% CI: 0.60–1.05). Malaria was not associated with differences in weight or height gain.

Conclusions

Chronic malnutrition remains a problem in rural Gambia, particularly among the poor and Fula ethnic group, but it was not associated with an increased risk of malaria.

Trial registration

Trial registration: ISRCTN, ISRCTN01738840, registered: 27/08/2010 (Retrospectively registered).

Comparison of registered and published intervention fidelity assessment in cluster randomised trials of public health interventions in low- and middle-income countries: systematic review

BACKGROUND

Cluster randomised trials (CRTs) are a key instrument to evaluate public health interventions. Fidelity assessment examines study processes to gauge whether an intervention was delivered as initially planned. Evaluation of implementation fidelity (IF) is required to establish whether the measured effects of a trial are due to the intervention itself and may be particularly important for CRTs of complex interventions conducted in low- and middle-income countries (LMICs). However, current CRT reporting guidelines offer no guidance on IF assessment. The objective of this review was to study current practices concerning the assessment of IF in CRTs of public health interventions in LMICs.

METHODS

CRTs of public health interventions in LMICs that planned or reported IF assessment in either the trial protocol or the main trial report were included. The MEDLINE/PubMed, CINAHL and EMBASE databases were queried from January 2012 to May 2016. To ensure availability of a study protocol, CRTs reporting a registration number in the abstract were included. Relevant data were extracted from each study protocol and trial report by two researchers using a predefined screening sheet. Risk of bias for individual studies was assessed.

RESULTS

We identified 90 CRTs of public health interventions in LMICs with a study protocol in a publicly available trial registry published from January 2012 to May 2016. Among these 90 studies, 25 (28%) did not plan or report assessing IF; the remaining 65 studies (72%) addressed at least one IF dimension. IF assessment was planned in 40% (36/90) of trial protocols and reported in 71.1% (64/90) of trial reports. The proportion of overall agreement between the trial protocol and trial report concerning occurrence of IF assessment was 66.7% (60/90). Most studies had low to moderate risk of bias.

CONCLUSIONS

IF assessment is not currently a systematic practice in CRTs of public health interventions carried out in LMICs. In the absence of IF assessment, it may be difficult to determine if CRT results are due to the intervention design, to its implementation, or to unknown or external factors that may influence results. CRT reporting guidelines should promote IF assessment.

TRIAL REGISTRATION

Protocol published and available at: https://doi.org/10.1186/s13643-016-0351-0.

Emergence of knock-down resistance in the Anopheles gambiae complex in the Upper River Region, The Gambia, and its relationship with malaria infection in children

BACKGROUND

Insecticide resistance threatens malaria control in sub-Saharan Africa. Knockdown resistance to pyrethroids and organochlorines in Anopheles gambiae sensu lato (s.l.) is commonly caused by mutations in the gene encoding a voltage-gated sodium channel which is the target site for the insecticide. The study aimed to examine risk factors for knockdown resistance in An. gambiae s.l. and its relationship with malaria infection in children in rural Gambia. Point mutations at the Vgsc-1014 locus, were measured in An. gambiae s.l. during a 2-year trial. Cross-sectional surveys were conducted at the end of the transmission season to measure malaria infection in children aged 6 months-14 years.

RESULTS

Whilst few Anopheles arabiensis and Anopheles coluzzii had Vgsc-1014 mutations, the proportion of An. gambiae sensu stricto (s.s.) mosquitoes homozygous for the Vgsc-1014F mutation increased from 64.8 to 90.9% during the study. The Vgsc-1014S or 1014F mutation was 80% higher in 2011 compared to 2010, and 27% higher in the villages with indoor residual spraying compared to those without. An increase in the proportion of An. gambiae s.l. mosquitoes with homozygous Vgsc-1014F mutations and an increase in the proportion of An. gambiae s.s. in a cluster were each associated with increased childhood malaria infection. Homozygous Vgsc-1014F mutations were, however, most common in An. gambiae s.s. and almost reached saturation during the study meaning that the two variables were colinear.

CONCLUSIONS

As a result of colinearity between homozygous Vgsc-1014F mutations and An. gambiae s.s., it was not possible to determine whether insecticide resistance or species composition increased the risk of childhood malaria infection.

Effectiveness of a long-lasting piperonyl butoxide-treated insecticidal net and indoor residual spray interventions, separately and together, against malaria transmitted by pyrethroid-resistant mosquitoes: a cluster, randomised controlled, two-by-two factorial design trial

BACKGROUND

Progress in malaria control is under threat by wide-scale insecticide resistance in malaria vectors. Two recent vector control products have been developed: a long-lasting insecticidal net that incorporates a synergist piperonyl butoxide (PBO) and a long-lasting indoor residual spraying formulation of the insecticide pirimiphos-methyl. We evaluated the effectiveness of PBO long-lasting insecticidal nets versus standard long-lasting insecticidal nets as single interventions and in combination with the indoor residual spraying of pirimiphos-methyl.

METHODS

We did a four-group cluster randomised controlled trial using a two-by-two factorial design of 48 clusters derived from 40 villages in Muleba (Kagera, Tanzania). We randomly assigned these clusters using restricted randomisation to four groups: standard long-lasting insecticidal nets, PBO long-lasting insecticidal nets, standard long-lasting insecticidal nets plus indoor residual spraying, or PBO long-lasting insecticidal nets plus indoor residual spraying. Both standard and PBO nets were distributed in 2015. Indoor residual spraying was applied only once in 2015. We masked the inhabitants of each cluster to the type of nets received, as well as field staff who took blood samples. Neither the investigators nor the participants were masked to indoor residual spraying. The primary outcome was the prevalence of malaria infection in children aged 6 months to 14 years assessed by cross-sectional surveys at 4, 9, 16, and 21 months after intervention. The endpoint for assessment of indoor residual spraying was 9 months and PBO long-lasting insecticidal nets was 21 months. This trial is registered with ClinicalTrials.gov, number NCT02288637.

FINDINGS

7184 (68·0%) of 10 560 households were selected for post-intervention survey, and 15 469 (89·0%) of 17 377 eligible children from the four surveys were included in the intention-to-treat analysis. Of the 878 households visited in the two indoor residual spraying groups, 827 (94%) had been sprayed. Reported use of long-lasting insecticidal nets, across all groups, was 15 341 (77·3%) of 19 852 residents after 1 year, decreasing to 12 503 (59·2%) of 21 105 in the second year. Malaria infection prevalence after 9 months was lower in the two groups that received PBO long-lasting insecticidal nets than in the two groups that received standard long-lasting insecticidal nets (531 [29%] of 1852 children vs 767 [42%] of 1809; odds ratio [OR] 0·37, 95% CI 0·21-0·65; p=0·0011). At the same timepoint, malaria prevalence in the two groups that received indoor residual spraying was lower than in groups that did not receive indoor residual spraying (508 [28%] of 1846 children vs 790 [44%] of 1815; OR 0·33, 95% CI 0·19-0·55; p<0·0001) and there was evidence of an interaction between PBO long-lasting insecticidal nets and indoor residual spraying (OR 2·43, 95% CI 1·19-4·97; p=0·0158), indicating redundancy when combined. The PBO long-lasting insecticidal net effect was sustained after 21 months with a lower malaria prevalence than the standard long-lasting insecticidal net (865 [45%] of 1930 children vs 1255 [62%] of 2034; OR 0·40, 0·20-0·81; p=0·0122).

INTERPRETATION

The PBO long-lasting insecticidal net and non-pyrethroid indoor residual spraying interventions showed improved control of malaria transmission compared with standard long-lasting insecticidal nets where pyrethroid resistance is prevalent and either intervention could be deployed to good effect. As a result, WHO has since recommended to increase coverage of PBO long-lasting insecticidal nets. Combining indoor residual spraying with pirimiphos-methyl and PBO long-lasting insecticidal nets provided no additional benefit compared with PBO long-lasting insecticidal nets alone or standard long-lasting insecticidal nets plus indoor residual spraying.

FUNDING

UK Department for International Development, Medical Research Council, and Wellcome Trust.

Comparative effectiveness of malaria prevention measures: a systematic review and network meta-analysis

Background

Malaria causes significant morbidity and mortality worldwide. There are several preventive measures that are currently employed, including insecticide-treated nets (ITNs, including long-lasting insecticidal nets and insecticidal-treated bed nets), indoor residual spraying (IRS), prophylactic drugs (PD), and untreated nets (UN). However, it is unclear which measure is the most effective for malaria prevention. We therefore undertook a network meta-analysis to compare the efficacy of different preventive measures on incidence of malaria infection.

Methods

A systematic literature review was undertaken across four medical and life sciences databases (PubMed, Cochrane Central, Embase, and Web of Science) from their inception to July 2016 to compare the effectiveness of different preventive measures on malaria incidence. Data from the included studies were analysed for the effectiveness of several measures against no intervention (NI). This was carried out using an automated generalized pairwise modeling (GPM) framework for network meta-analysis to generate mixed treatment effects against a common comparator of no intervention (NI).

Results

There were 30 studies that met the inclusion criteria from 1998–2016. The GPM framework led to a final ranking of effectiveness of measures in the following order from best to worst: PD, ITN, IRS and UN, in comparison with NI. However, only ITN (RR: 0.49, 95% CI: 0.32–0.74) showed precision while other methods [PD (RR: 0.24, 95% CI: 0.004–15.43), IRS (RR: 0.55, 95% CI: 0.20–1.56) and UN (RR: 0.73, 95% CI: 0.28–1.90)] demonstrating considerable uncertainty associated with their point estimates.

Conclusion

Current evidence is strong for the protective effect of ITN interventions in malaria prevention. Even though ITNs were found to be the only preventive measure with statistical support for their effectiveness, the role of other malaria control measures may be important adjuncts in the global drive to eliminate malaria.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2783-y) contains supplementary material, which is available to authorized users.

Reactive community-based self-administered treatment against residual malaria transmission: study protocol for a randomized controlled trial

Background

Systematic treatment of all individuals living in the same compound of a clinical malaria case may clear asymptomatic infections and possibly reduce malaria transmission, where this is focal. High and sustained coverage is extremely important and requires active community engagement. This study explores a community-based approach to treating malaria case contacts.

Methods/design

This is a cluster-randomized trial to determine whether, in low-transmission areas, treating individuals living in the same compound of a clinical malaria case with dihydroartemisinin-piperaquine can reduce parasite carriage and thus residual malaria transmission. Treatment will be administered through the local health system with the approach of encouraging community participation designed and monitored through formative research. The trial goal is to show that this approach can reduce in intervention villages the prevalence of Plasmodium falciparum infection toward the end of the malaria transmission season.

Discussion

Adherence and cooperation of the local communities are critical for the success of mass treatment campaigns aimed at reducing malaria transmission. By exploring community perceptions of the changing trends in malaria burden, existing health systems, and reaction to self-administered treatment, this study will develop and adapt a model for community engagement toward malaria elimination that is cost-effective and fits within the existing health system.

Trial registration

Clinical trials.gov, NCT02878200. Registered on 25 August 2016. 

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2506-x) contains supplementary material, which is available to authorized users.

Combination of indoor residual spraying with long-lasting insecticide-treated nets for malaria control in Zambezia, Mozambique: a cluster randomised trial and cost-effectiveness study protocol

Background

Most of the reduction in malaria prevalence seen in Africa since 2000 has been attributed to vector control interventions. Yet increases in the distribution and intensity of insecticide resistance and higher costs of newer insecticides pose a challenge to sustaining these gains. Thus, endemic countries face challenging decisions regarding the choice of vector control interventions.

Methods

A cluster randomised trial is being carried out in Mopeia District in the Zambezia Province of Mozambique, where malaria prevalence in children under 5 is high (68% in 2015), despite continuous and campaign distribution of long-lasting insecticide-treated nets (LLINs). Study arm 1 will continue to use the standard, LLIN-based National Malaria Control Programme vector control strategy (LLINs only), while study arm 2 will receive indoor residual spraying (IRS) once a year for 2 years with a microencapsulated formulation of pirimiphos-methyl (Actellic 300 CS), in addition to the standard LLIN strategy (LLINs+IRS). Prior to the 2016 IRS implementation (the first of two IRS campaigns in this study), 146 clusters were defined and stratified per number of households. Clusters were then randomised 1:1 into the two study arms. The public health impact and cost-effectiveness of IRS intervention will be evaluated over 2 years using multiple methods: (1) monthly active malaria case detection in a cohort of 1548 total children aged 6-59 months; (2) enhanced passive surveillance at health facilities and with community health workers; (3) annual cross-sectional surveys; and (4) entomological surveillance. Prospective microcosting of the intervention and provider and societal costs will be conducted. Insecticide resistance status pattern and changes in local Anopheline populations will be included as important supportive outcomes.

Discussion

By evaluating the public health impact and cost-effectiveness of IRS with a non-pyrethroid insecticide in a high-transmission setting with high LLIN ownership, it is expected that this study will provide programmatic and policy-relevant data to guide national and global vector control strategies.

Trial registration number

NCT02910934.

An observational analysis of the impact of indoor residual spraying with non-pyrethroid insecticides on the incidence of malaria in Ségou Region, Mali: 2012-2015

Background

Ségou Region in Central Mali is an area of high malaria burden with seasonal transmission, high access to and use of long-lasting insecticidal nets (LLINs), and resistance to pyrethroids and DDT well documented in Anopheles gambiae s.l. (the principal vector of malaria in Mali). Ségou has recently received indoor residual spraying (IRS) supported by Mali’s collaboration with the US President’s Malaria Initiative/Africa Indoor Residual Spraying programme. From 2012 to 2015, two different non-pyrethroid insecticides: bendiocarb in 2012 and 2013 and pirimiphos-methyl in 2014 and 2015, were used for IRS in two districts. This report summarizes the results of observational analyses carried out to assess the impact of these IRS campaigns on malaria incidence rates reported through local and district health systems before and after spraying.

Methods

A series of retrospective time series analyses were performed on 1,382,202 rapid diagnostic test-confirmed cases of malaria reported by district routine health systems in Ségou Region from January 2012 to January 2016. Malaria testing, treatment, surveillance and reporting activities remained consistent across districts and years during the study period, as did LLIN access and use estimates as well as An. gambiae s.l. insecticide resistance patterns. Districts were stratified by IRS implementation status and all-age monthly incidence rates were calculated and compared across strata from 2012 to 2014. In 2015 a regional but variable scale-up of seasonal malaria chemoprevention complicated the region-wide analysis; however IRS operations were suspended in Bla District that year so a difference in differences approach was used to compare 2014 to 2015 changes in malaria incidence at the health facility level in children under 5-years-old from Bla relative to changes observed in Barouéli, where IRS operations were consistent.

Results

During 2012–2014, rapid reductions in malaria incidence were observed during the 6 months following each IRS campaign, though most of the reduction in cases (70% of the total) was concentrated in the first 2 months after each campaign was completed. Compared to non-IRS districts, in which normal seasonal patterns of malaria incidence were observed, an estimated 286,745 total fewer cases of all-age malaria were observed in IRS districts. The total cost of IRS in Ségou was around 9.68 million USD, or roughly 33.75 USD per case averted. Further analysis suggests that the timing of the 2012–2014 IRS campaigns (spraying in July and August) was well positioned to maximize public health impact. Suspension of IRS in Bla District after the 2014 campaign resulted in a 70% increase in under-5-years-old malaria incidence rates from 2014 to 2015, significantly greater (p = 0.0003) than the change reported from Barouéli District, where incidence rates remained the same.

Conclusions

From 2012 to 2015, the annual IRS campaigns in Ségou are associated with several hundred thousand fewer cases of malaria. This work supports the growing evidence that shows that IRS with non-pyrethroid insecticides is a wise public health investment in areas with documented pyrethroid resistance, high rates of LLIN coverage, and where house structures and population densities are appropriate. Additionally, this work highlights the utility of quality-assured and validated routine surveillance and well defined observational analyses to rapidly assess the impact of malaria control interventions in operational settings, helping to empower evidence-based decision making and to further grow the evidence base needed to better understand when and where to utilize new vector control tools as they become available.

Electronic supplementary material

The online version of this article (10.1186/s12936-017-2168-2) contains supplementary material, which is available to authorized users.

Modern Vector Control

The rapid spread of mosquito resistance to currently available insecticides, and the current lack of an efficacious malaria vaccine are among many challenges that affect large-scale efforts for malaria control. As goals of malaria elimination and eradication are put forth, new vector-control paradigms and tools and/or further optimization of current vector-control products are required to meet public health demands. Vector control remains the most effective measure to prevent malaria transmission and present gains against malaria mortality and morbidity may be maintained as long as vector-intervention strategies are sustained and adapted to underlying vector-related transmission dynamics. The following provides a brief overview of vector-control strategies and tools either in use or under development and evaluation that are intended to exploit key entomological parameters toward driving down transmission.

Determination of the residual efficacy of carbamate and organophosphate insecticides used for indoor residual spraying for malaria control in Ethiopia

Background

Indoor residual spraying is one of the key vector control interventions for malaria control in Ethiopia. As malaria transmission is seasonal in most parts of Ethiopia, a single round of spraying can usually provide effective protection against malaria, provided the insecticide remains effective over the entire malaria transmission season. This experiment was designed to evaluate the residual efficacy of bendiocarb, pirimiphos-methyl, and two doses of propoxur on four different wall surfaces (rough mud, smooth mud, dung, and paint). Filter papers affixed to wall surfaces prior to spraying were analyzed to determine the actual concentration applied. Cone bioassays using a susceptible Anopheles arabiensis strain were done monthly to determine the time for which insecticides were effective in killing mosquitoes.

Results

The mean insecticide dosage of bendiocarb applied to walls was 486 mg/m² (target 400/mg). This treatment lasted 1 month or less on rough mud, smooth mud, and dung, but 4 months on painted surfaces. Pirimiphos-methyl was applied at 1854 mg/m² (target 1000 mg/m²), and lasted between 4 and 6 months on all wall surfaces. Propoxur with a target dose of 1000 mg/m² was applied at 320 mg/m², and lasted 2 months or less on all surfaces, except painted surfaces (4 months). Propoxur with a target dose of 2000 mg/m², was applied at 638 mg/m², and lasted 3 months on rough mud, but considerably longer (5–7 months) on the other substrates.

Conclusions

It would appear that the higher dose of propoxur and pirimiphos-methyl correspond best to the Ethiopian transmission season, although interactions between insecticide and the substrate should be taken into account as well. However, the insecticide quantification revealed that the dosages actually applied differed considerably from the target dosages, even though care was taken in the mixing of insecticide formulations and spraying of the walls. It is unclear whether this variability is due to initial concentrations of insecticides, poor application, or other factors. Further work is needed to ensure that target doses are correctly applied, both operationally and in insecticide evaluations.

Electronic supplementary material

The online version of this article (10.1186/s12936-017-2122-3) contains supplementary material, which is available to authorized users.

The protective effectiveness of control interventions for malaria prevention: a systematic review of the literature

Background: Thanks to a considerable increase in funding, malaria control interventions (MCI) whose efficacy had been demonstrated by controlled trials have been largely scaled up during the last decade. Nevertheless, it was not systematically investigated whether this efficacy had been preserved once deployed on the field. Therefore, we sought the literature to assess the disparities between efficacy and effectiveness and the effort to measure the protective effectiveness (PE) of MCI.

Methods: The PubMed database was searched for references with keywords related to malaria, to control interventions for prevention and to study designs that allow for the measure of the PE against parasitemia or against clinical outcomes.

Results: Our search retrieved 1423 references, and 162 articles were included in the review. Publications were scarce before the year 2000 but dramatically increased afterwards. Bed nets was the MCI most studied (82.1%). The study design most used was a cross-sectional study (65.4%). Two thirds (67.3%) were conducted at the district level or below, and the majority (56.8%) included only children even if the MCI didn’t target only children. Not all studies demonstrated a significant PE from exposure to MCI: 60.6% of studies evaluating bed nets, 50.0% of those evaluating indoor residual spraying, and 4/8 showed an added PE of using both interventions as compared with one only; this proportion was 62.5% for intermittent preventive treatment of pregnant women, and 20.0% for domestic use of insecticides.

Conclusions: This review identified numerous local findings of low, non-significant PE –or even the absence of a protective effect provided by these MCIs. The identification of such failures in the effectiveness of MCIs advocates for the investigation of the causes of the problem found. Ideal evaluations of the PE of MCIs should incorporate both a large representativeness and an evaluation of the PE stratified by subpopulations.

Resurgence of Malaria Following Discontinuation of Indoor Residual Spraying of Insecticide in an Area of Uganda With Previously High-Transmission Intensity

BACKGROUND

Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are the primary tools for malaria prevention in Africa. It is not known whether reductions in malaria can be sustained after IRS is discontinued. Our aim in this study was to assess changes in malaria morbidity in an area of Uganda with historically high transmission where IRS was discontinued after a 4-year period followed by universal LLIN distribution.

METHODS

Individual-level malaria surveillance data were collected from 1 outpatient department and 1 inpatient setting in Apac District, Uganda, from July 2009 through November 2015. Rounds of IRS were delivered approximately every 6 months from February 2010 through May 2014 followed by universal LLIN distribution in June 2014. Temporal changes in the malaria test positivity rate (TPR) were estimated during and after IRS using interrupted time series analyses, controlling for age, rainfall, and autocorrelation.

RESULTS

Data include 65 421 outpatient visits and 13 955 pediatric inpatient admissions for which a diagnostic test for malaria was performed. In outpatients aged <5 years, baseline TPR was 60%-80% followed by a rapid and then sustained decrease to 15%-30%. During the 4-18 months following discontinuation of IRS, absolute TPR values increased by an average of 3.29% per month (95% confidence interval, 2.01%-4.57%), returning to baseline levels. Similar trends were seen in outpatients aged ≥5 years and pediatric admissions.

CONCLUSIONS

Discontinuation of IRS in an area with historically high transmission intensity was associated with a rapid increase in malaria morbidity to pre-IRS levels.

Reported community-level indoor residual spray coverage from two-stage cluster surveys in sub-Saharan Africa

Background

Malaria is an important cause of morbidity and mortality in malaria-endemic areas. Indoor residual spray is an effective intervention to control malaria, but high community-level coverage is needed to maximize its impact.

Methods and results

Using thirty-four two-stage cluster surveys (e.g., demographic and health surveys) and lot quality assurance sampling, indoor residual spray was estimated at the community level (i.e. enumeration-area) across sub-Saharan Africa since 2010. For communities receiving indoor residual spray a logistic regression predicted whether community-level coverage exceeded 50% or not. Household-level coverage was equitable both in terms of wealth and urban/rural, with poorer and rural houses more likely to be sprayed than richer and urban houses. Coverage of indoor residual spray at the community level is poor across the continent, with 54% of communities receiving the intervention not reaching 50% coverage. Having >50% coverage at the community-level was not associated with increasing the number of houses sprayed in the country.

Conclusions

Implementation and monitoring of indoor residual coverage at small geographical scales need to improve greatly to receive maximum benefit of the intervention.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1893-x) contains supplementary material, which is available to authorized users.

Insecticide-treated durable wall lining (ITWL): future prospects for control of malaria and other vector-borne diseases

While long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the cornerstones of malaria vector control throughout sub-Saharan Africa, there is an urgent need for the development of novel insecticide delivery mechanisms to sustain and consolidate gains in disease reduction and to transition towards malaria elimination and eradication. Insecticide-treated durable wall lining (ITWL) may represent a new paradigm for malaria control as a potential complementary or alternate longer-lasting intervention to IRS. ITWL can be attached to inner house walls, remain efficacious over multiple years and overcome some of the operational constraints of first-line control strategies, specifically nightly behavioural compliance required of LLINs and re-current costs and user fatigue associated with IRS campaigns. Initial experimental hut trials of insecticide-treated plastic sheeting reported promising results, achieving high levels of vector mortality, deterrence and blood-feeding inhibition, particularly when combined with LLINs. Two generations of commercial ITWL have been manufactured to date containing either pyrethroid or non-pyrethroid formulations. While some Phase III trials of these products have demonstrated reductions in malaria incidence, further large-scale evidence is still required before operational implementation of ITWL can be considered either in a programmatic or more targeted community context. Qualitative studies of ITWL have identified aesthetic value and observable entomological efficacy as key determinants of household acceptability. However, concerns have been raised regarding installation feasibility and anticipated cost-effectiveness. This paper critically reviews ITWL as both a putative mechanism of house improvement or more conventional intervention and discusses its future prospects as a method for controlling malaria and other vector-borne diseases.

False-negative malaria rapid diagnostic tests in Rwanda: impact of Plasmodium falciparum isolates lacking hrp2 and declining malaria transmission

Background

Rapid diagnostic tests (RDTs) for histidine rich protein 2 (HRP2) are often used to determine whether persons with fever should be treated with anti-malarials. However, Plasmodium falciparum parasites with a deletion of the hrp2 gene yield false-negative RDTs and there are concerns the sensitivity of HRP2-based RDTs may fall when the intensity of transmission decreases.

Methods

This observational study enrolled 9226 patients at three health centres in Rwanda from April 2014 to April 2015. It then compared the sensitivity of RDTs based on HRP2 and the Plasmodium lactate dehydrogenase (pLDH) to microscopy (thick smears) for the diagnosis of malaria. PCR was used to determine whether deletions of the histidine-rich central repeat region of the hrp2 gene (exon 2) were associated with false-negative HRP2-based RDTs.

Results

In comparison to microscopy, the sensitivity and specificity of HRP2- and pLDH-based RDTs were 89.5 and 86.2% and 80.2 and 94.3%, respectively. When the results for both RDTs were combined, sensitivity rose to 91.8% and specificity was 85.7%. Additionally, when smear positivity fell from 46 to 3%, the sensitivity of the HRP2-based RDT fell from 88 to 67%. Of 370 samples with false-negative HRP2 RDT results for which PCR was performed, 140 (38%) were identified as P. falciparum by PCR. Of the isolates identified as P. falciparum by PCR, 32 (23%) were negative for the hrp2 gene based on PCR. Of the 32 P. falciparum isolates negative for hrp2 by PCR, 17 (53%) were positive based on the pLDH RDT.

Conclusion

This prospective study of RDT performance coincided with a decline in the intensity of malaria transmission in Kibirizi (fall in slide positivity from 46 to 3%). This decline was associated with a decrease in HRP2 RDT sensitivity (from 88 to 67%). While P. falciparum isolates without the hrp2 gene were an important cause of false-negative HRP2-based RDTs, most were identified by the pLDH-based RDT. Although WHO does not recommend the use of combined HRP2/pLDH testing in sub-Saharan Africa, these results suggest that combination HRP2/pLDH-based RDTs could reduce the impact of false-negative HRP2-based RDTs for detection of symptomatic P. falciparum malaria.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1768-1) contains supplementary material, which is available to authorized users.