Blinding trachoma: prevention with the safe strategy

Individual longitudinal compliance to neglected tropical disease mass drug administration programmes, a systematic review

Repeated distribution of preventative chemotherapy (PC) by mass drug administration forms the mainstay of transmission control for five of the 20 recognised neglected tropical diseases (NTDs); soil-transmitted helminths, schistosomiasis, lymphatic filariasis, onchocerciasis and trachoma. The efficiency of such programmes is reliant upon participants swallowing the offered treatment consistently at each round. This is measured by compliance, defined as the proportion of eligible participants swallowing treatment. Individually linked longitudinal compliance data is important for assessing the potential impact of MDA-based control programmes, yet this accurate monitoring is rarely implemented in those for NTDs. Longitudinal compliance data reported by control programmes globally for the five (PC)-NTDs since 2016 is examined, focusing on key associations of compliance with age and gender. PubMed and Web of Science was searched in January 2022 for articles written in English and Spanish, and the subsequent extraction adhered to PRISMA guidelines. Study title screening was aided by Rayyan, a machine learning software package. Studies were considered for inclusion if primary compliance data was recorded for more than one time point, in a population larger than 100 participants. All data analysis was conducted in R. A total of 89 studies were identified containing compliance data, 57 were longitudinal studies, of which 25 reported individually linked data reported by varying methods. The association of increasing age with the degree of systematic treatment was commonly reported. The review is limited by the paucity of data published on this topic. The varying and overlapping terminologies used to describe coverage (receiving treatment) and compliance (swallowing treatment) is reviewed. Consequently, it is recommended that WHO considers clearly defining the terms for coverage, compliance, and longitudinal compliance which are currently contradictory across their NTD treatment guidelines. This review is registered with PROSPERO (number: CRD42022301991).

Modeling the "F" in "SAFE": The dynamic game of facial cleanliness in trachoma prevention

Trachoma, a neglected tropical disease (NTDs) caused by bacterium Chlamydia trachomatis, is a leading cause of infectious blindness. Efforts are underway to eliminate trachoma as a public health problem by using the "SAFE" strategy. While mathematical models are now standard tools used to support elimination efforts and there are a variety of models studying different aspects of trachoma transmission dynamics, the "F" component of the strategy corresponding to facial cleanliness has received very little attention so far. In this paper, we incorporate human behavior into a standard epidemiological model and develop a dynamical game during which individuals practice facial cleanliness based on their epidemiological status and perceived benefits and costs. We found that the number of infectious individuals generally increases with the difficulty to access a water source. However, this increase happens only during three transition periods and the prevalence stays constant otherwise. Consequently, improving access to water can help eliminate trachoma, but the improvement needs to be significant enough to cross at least one of the three transition thresholds; otherwise the improved access will have no noticeable effect.

Low prevalence of active trachoma and associated factors among children aged 1-9 years in rural communities of Metema District, Northwest Ethiopia: a community based cross-sectional study

BACKGROUND

Trachoma is an infectious disease of the eye caused by Chlamydia trachomatis and transmitted via contact with eye discharge from infected persons and leading to blindness worldwide. Children less than 9 years of age affected more seriously. The disease is common where access to water and sanitation are limited.

OBJECTIVE

To determine the prevalence of active trachoma and associated factors among children aged 1-9 years in rural communities of Metema District, West Gondar Zone, Northwest Ethiopia.

METHOD

A community based cross-sectional study design was used to collect data from 792 children aged 1-9 years old in Metema district from April to May 2018. Multistage sampling technique was used to select the study participants. Pretested interviewer-administered structured questionnaire and eye examination using binocular loupe to differentiate trachoma cases was the data collection methods and tools. The bivariable and multivariable binary logistic regression model was employed for analysis. P-value < 0.05 was considered to declare statistical significance.

RESULTS

A total of 752 children aged l-9 years were enrolled in this study with response rate of 94.9%. The overall prevalence of active trachoma among the study participants was 11.8% (95% CI, 9.5-13.9). Unprotected source of water (AOR = 4.7; 95% CI: 2.5-8.9), lower household water consumption (AOR = 2.8; 95% CI: 1.3-6.0), improper latrine utilization (AOR = 3.2; 95% CI: 1.5-6.7), and frequency of face washing once per day (AOR = 5.3; 95% CI: 1.2-26.6) were the factors significantly associated with active trachoma.

CONCLUSION

The current study revealed a lower overall prevalence of active trachoma (11.8%) than the WHO threshold prevalence (20%) used to declare it as a severe public health problem. All residents and health professional should collaborate on trachoma prevention by implementing the WHO SAFE strategy- surgery for trichiasis, antibiotics, facial cleanliness and environmental improvement for further trachoma elimination.

WASH Upgrades for Health in Amhara (WUHA): study protocol for a cluster-randomised trial in Ethiopia

INTRODUCTION

Facial hygiene promotion and environmental improvements are central components of the global trachoma elimination strategy despite a lack of experimental evidence supporting the effectiveness of water, sanitation and hygiene (WASH) measures for reducing trachoma transmission. The objective of the WUHA (WASH Upgrades for Health in Amhara) trial is to evaluate if a comprehensive water improvement and hygiene education programme reduces the prevalence of ocular chlamydia infection in rural Africa.

METHODS AND ANALYSIS

Forty study clusters, each of which had received at least annual mass azithromycin distributions for the 7 years prior to the start of the study, are randomised in a 1:1 ratio to the WASH intervention arm or a delayed WASH arm. The WASH package includes a community water point, community-based hygiene promotion workers, household wash stations, household WASH education books, household soap distribution and a primary school hygiene curriculum. Educational activities emphasise face-washing and latrine use. Mass antibiotic distributions are not provided during the first 3 years but are provided annually over the final 4 years of the trial. Annual monitoring visits are conducted in each community. The primary outcome is PCR evidence of ocular chlamydia infection among children aged 0-5 years, measured in a separate random sample of children annually over 7 years. A secondary outcome is improvement of the clinical signs of trachoma between the baseline and final study visits as assessed by conjunctival photography. Laboratory workers and photo-graders are masked to treatment allocation.

ETHICS AND DISSEMINATION

Study protocols have been approved by human subjects review boards at the University of California, San Francisco, Emory University, the Ethiopian Food and Drug Authority, and the Ethiopian Ministry of Innovation and Technology. A data safety and monitoring committee oversees the trial. Results will be disseminated through peer-reviewed publications and presentations.

TRIAL REGISTRATION NUMBER

(http://www.clinicaltrials.gov): NCT02754583; Pre-results.

Milestones in the fight to eliminate trachoma

PURPOSE

Trachoma, a chronic conjunctivitis that can result in vision loss from trichiasis, is targeted for global elimination by 2020. Several milestones in the long process towards elimination are noteworthy for the impact they have had on changing or accelerating progress. The purpose of this review is to describe the milestones and the impact they have had both for trachoma elimination and beyond.

FINDINGS

Eight milestones are presented. They are discovery of the causative agent; development of a clinical grading scheme; establishment of the World Health Organization Alliance for the Global Elimination of Trachoma by 2020; setting targets that define elimination; building an evidence base for trichiasis surgery; azithromycin donation programme; use of the SAFE strategy (Surgery, Antibiotics, Facial cleanliness, and Environmental improvement); and The Global Trachoma Mapping Project.

SUMMARY

These milestones have significantly pushed the progress towards elimination. Despite challenges to achieving the goal of elimination by 2020, there is continued commitment into the future to ensure that this preventable cause of blindness is no longer a threat.

Factors shaping the implementation of the SAFE strategy for trachoma using the Consolidated Framework for Implementation Research: a systematic review

Background: The SAFE strategy (surgery for trichiasis, antibiotics for active infection, facial cleanliness and environmental improvement) is the World Health Organization (WHO) recommended guideline for the elimination of blindness by trachoma by the year 2020.

Objective: While evaluations on the implementation of the SAFE strategy have been done, systematic reviews on the factors that have shaped implementation are lacking. This review sought to identify these factors.

Methods: We searched PUBMED, Google Scholar, CINAHL and Cochrane Collaboration to identify studies that had implemented SAFE interventions. The Consolidated Framework for Implementation Research (CFIR) guided development of the data extraction guide and data analysis.

Results: One hundred and thirty-seven studies were identified and only 10 papers fulfilled the eligibility criteria. Characteristics of the innovation – such as adaptation of the SAFE interventions to suit the setting and observability of positive health outcomes from pilots – increased local adoption. Characteristics of outer setting – which included strong multisectoral collaboration – were found to enhance implementation through the provision of resources necessary for programme activities. When community needs and resources were unaccounted for there was poor compatibility with local settings. Characteristics of the inner setting – such as poor staffing, high labour turnovers and lack of ongoing training – affected health workers’ implementation behaviour. Implementation climate within provider organisations was shaped by availability of resources. Characteristics of individuals – which included low knowledge levels – affected the acceptability of SAFE programmes; however, early adopters could be used as change agents. Finally, the use of engagement strategies tailored towards promoting community participation and stakeholder involvement during the implementation process facilitated adoption process.

Conclusion: We found CFIR to be a robust framework capable of identifying different implementation determinants in low resource settings. However, there is a need for more research on the organisational, provider and implementation process related factors for trachoma as most studies focused on the outer setting.

Epidemiology of trachoma and its implications for implementing the "SAFE" strategy in Somali Region, Ethiopia: results of 14 population-based prevalence surveys

Purpose: Ethiopia is highly trachoma endemic. Baseline mapping was needed in Ethiopia’s Somali Region to guide elimination efforts.

Methods: Cross-sectional community-based surveys were conducted in 34 suspected trachoma-endemic woredas, grouped as 14 evaluation units (EUs), using a standardised mapping methodology developed for the Global Trachoma Mapping Project.

Results: In total, 53,467 individuals were enumerated. A total of 48,058 (89.9%) were present at the time of survey teams’ visits and consented to examination. The prevalence of trachomatous inflammation–follicular (TF) among children aged 1–9 years ranged from 4.1% in the EU covering Danot, Boh, and Geladin woredas in Doolo Subzone to 38.1% in the EU covering Kebribeyah and Hareshen woredas in Fafan Subzone (East). The trichiasis prevalence among adults aged over 15 years varied from 0.1% in the EU covering Afder, Bare, and Dolobay woredas in Afder Subzone (West) to 1.2% in the EU covering Awbere in Fafan Subzone (West).

Conclusion: Mass drug administration (MDA) with azithromycin is needed in 13 EUs (population 2,845,818). Two EUs (population 667,599) had TF prevalences in 1–9-year-olds of ≥30% and will require at least 5 years of MDA; 5 EUs (population 1,1193,032) had TF prevalences of 10–29.9% and need at least three years of MDA; 6 EUs (population 985,187) had TF prevalences of 5–9.9% and need at least one round of azithromycin distribution before re-survey. In all 13 of these EUs, implementation of facial cleanliness and environmental improvement measures is also needed. Surveys are still needed in the remaining 34 unmapped woredas of Somali Region.

Village-Integrated Eye Worker trial (VIEW): rationale and design of a cluster-randomised trial to prevent corneal ulcers in resource-limited settings

INTRODUCTION

Corneal opacity is a leading cause of blindness worldwide. In resource-limited settings, untreated traumatic corneal abrasions may result in infection and ultimately, opacity. Although antimicrobial treatment of corneal ulcers may successfully cure infections, the scarring that accompanies the resolution of infection can still result in visual impairment. Prevention may be the optimal approach for reducing corneal blindness. Studies have employed community health workers to provide prompt administration of antimicrobials after corneal abrasions to prevent infections, but these studies were not designed to determine the effectiveness of such a programme.

METHODS AND ANALYSIS

The Village-Integrated Eye Worker trial (VIEW) is a cluster-randomised trial designed to assess the effectiveness of a community health worker intervention to prevent corneal ulcers. Twenty-four Village Development Committees (VDCs) in Nepal were randomised to receive a corneal ulcer prevention programme or to no intervention. Female Community Health Volunteers (FCHVs) in intervention VDCs are trained to diagnose corneal abrasions, provide antimicrobials and to refer participants when needed. An annual census is conducted over 3 years in all study VDCs to assess the incidence of corneal ulceration via corneal photography (primary outcome). Masked outcome assessors grade corneal photographs to determine the presence or absence of incident corneal opacities. The primary analysis is negative binomial regression to compare the incidence of corneal ulceration by study arm.

ETHICS AND DISSEMINATION

The University of California San Francisco Committee on Human Research, Nepal Netra Jyoti Sangh and the Nepal Health Research Council have given ethical approval for the trial. The results of this trial will be presented at local and international meetings and submitted to peer-reviewed journals for publication.

TRIAL REGISTRATION NUMBER

NCT01969786; Pre-results.

Baseline trachoma prevalence in Guinea: Results of national trachoma mapping in 31 health districts

Background

Based on previous studies, historical records and risk factors, trachoma was suspected to be endemic in 31 health districts (HDs) in Guinea. To facilitate planning for the elimination of trachoma as a public health problem, national trachoma surveys were conducted between 2011 and 2016 to determine the prevalence of trachomatous inflammation—follicular (TF) and trachomatous trichiasis (TT) in all 31 endemic HDs.

Methodology/Principal findings

A total of 27 cross-sectional surveys were conducted, each using two-stage cluster sampling (one survey in 2011 covered five HDs). Children aged 1–9 years and adults aged ≥15 years were examined for TF and TT, respectively, using the World Health Organization (WHO) simplified grading system. Indicators of household access to water, sanitation and hygiene (WASH) were also collected. A total of 100,051 people from 13,725 households of 556 clusters were examined, of whom 44,899 were male and 55,152 were female. 44,209 children aged 1–9-years and 48,745 adults aged ≥15 years were examined. The adjusted prevalence of TF varied between 1.0% (95%CI: 0.6–1.5%) to 41.8% (95%CI: 39.4–44.2%), while the adjusted prevalence of TT ranged from 0.0% (95%CI: 0.0–0.2%) to 2.8% (95%CI: 2.3–3.5%) in the 27 surveys. In all, 18 HDs had a TF prevalence ≥5% in children aged 1–9 years and 21 HDs had a TT prevalence ≥0.2% in adults aged ≥15 years. There were an estimated 32,737 (95% CI: 19,986–57,811) individuals with TT living in surveyed HDs at the time of surveys.

Conclusions/Significance

Trachoma is a public health problem in Guinea. 18 HDs required intervention with at least one round of mass drug administration and an estimated 32,737 persons required TT surgery in the country. The results provided clear evidence for Guinea to plan for national trachoma elimination.

Trachoma is the leading infectious cause of blindness worldwide. The World Health Organization (WHO) recommends that endemic countries implement the SAFE strategy (surgery for trichiasis, antibiotic treatment, facial cleanliness and environmental improvement) to achieve trachoma elimination by the year 2020. Trachoma was suspected to be endemic in Guinea in 31 health districts except those in and around the capital Conakry, based on historical records and previous studies. To facilitate planning for the elimination of trachoma as a public health problem, Guinea conducted 27 separate trachoma surveys between 2011 and 2016 to determine the prevalence of trachomatous inflammation—follicular (TF) and trachomatous trichiasis (TT) in these 31 health districts. The results showed 18 health districts requiring intervention with at least one round of mass drug administration and an estimated 32,737 persons requiring TT surgery in the country. These data provided clear evidence for Guinea to plan for national trachoma elimination.

Xanthatin inhibits corneal neovascularization by inhibiting the VEGFR2‑mediated STAT3/PI3K/Akt signaling pathway

Alkali burn is one of the main causes of corneal injury. The inflammation and neovascularization caused by alkali burns aggravate corneal damage, resulting in loss of vision. The aim of the present study was to evaluate the efficacy of xanthatin in the treatment of alkali burn-induced inflammation and neovascularization. A CCK-8 assay was used to detect the effects of different concentrations of xanthatin on the proliferation of human umbilical vein endothelial cells (HUVECs). The effects of xanthatin on the migration of HUVECs and the ability of lumen formation were examined using a scratch test and lumen formation assay, respectively. A total of 60 Sprague-Dawley rats were randomly divided into two groups to establish a corneal alkali burn model, and were treated with PBS and xanthatin eye drops four times a day. A slit lamp microscope recorded changes of the cornea at 0, 4, 7, 10 and 14 days, and the inflammatory indices of the cornea and the neovascular area were evaluated. The expression levels of vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF) in the cornea under different treatment conditions were detected using immunofluorescence and western blot analysis. In order to investigate the mechanism of xanthatin on the inhibition of inflammation and neovascularization, HUVECs were treated with xanthatin and PBS following VEGF treatment. The subcellular localization of signal transducer and activator of transcription 3 (STAT3) was detected using immunofluorescence. The expression levels of VEGF receptor 2 (VEGFR2), STAT3, phosphoinositide 3-kinase (PI3K) and Akt were detected using western blot analysis. The results revealed that xanthatin inhibited the proliferation of HUVECs in a concentration-dependent manner. The migration ability and lumen-forming ability of the HUVECs were also inhibited by xanthatin. Slit lamp microscopy showed that the inflammatory index and the area of neovascularization in the xanthatin-treated group were significantly reduced, compared with those in the PBS treatment group. The xanthatin treatment group exhibited a lower protein expression level of VEGF and increased protein expression level of PEDF, compared with the PBS treatment group. In the VEGF-treated HUVECs, xanthatin significantly decreased the expression levels of p-VEGFR2, phosphorylated (p-)STAT3, p-PI3K and p-Akt. In conclusion, the present study confirmed that xanthatin inhibited corneal neovascularization and inflammation in the alkali burn model, elucidating the underlying mechanisms involved in its protective effects. Therefore, xanthatin may be a novel drug for the treatment of corneal alkali burn.

Prevalence of trachoma in the Kayes region of Mali eight years after stopping mass drug administration

BACKGROUND

In 2009, three years after stopping mass treatment with azithromycin, a trachoma impact survey in four health districts in the Kayes region of Mali found a prevalence of trachomatous inflammation-follicular (TF) among children aged 1 to 9 years of >5% and a trachomatous trichiasis (TT) prevalence within the general population (≥1-year-old) of <1%. As a result, the government's national trachoma program expanded trichiasis surgery and related activities required to achieve trachoma elimination.

METHODOLOGY/PRINCIPAL FINDINGS

In 2015, to assess progress towards elimination, a follow-up impact survey was conducted in the Kayes, Kéniéba, Nioro and Yélimané health districts. The survey used district level two-stage cluster random sampling methodology with 20 clusters of 30 households in each evaluation unit. Subjects were eligible for examination if they were ≥1 year. TF and TT cases were identified and confirmed by experienced ophthalmologists. In total 14,159 people were enumerated and 11,620 (82%) were examined. TF prevalence (95% confidence interval (CI)) was 0.5% (0.3-1%) in Kayes, 0.8% (0.4-1.7%) in Kéniéba, 0.2% (0-0.9%) in Nioro and 0.3% (0.1-1%) in Yélimané. TT prevalence (95% CI) was 0.04% (0-0.25%) in Kayes, 0.29% (0.11-0.6%) in Kéniéba, 0.04% (0-0.25%) in Nioro and 0.07% (0-0.27%) in Yélimané.

CONCLUSIONS/SIGNIFICANCE

Eight years after stopping MDA and intensifying trichiasis surgery outreach campaigns, all four districts reached the TF elimination threshold of <5% and three of four districts reached the TT elimination threshold of <0.1%.

Active trachoma and community use of sanitation, Ethiopia

Objective

To investigate, in Amhara, Ethiopia, the association between prevalence of active trachoma among children aged 1–9 years and community sanitation usage.

Methods

Between 2011 and 2014, prevalence of trachoma and household pit latrine usage were measured in five population-based cross-sectional surveys. Data on observed indicators of latrine use were aggregated into a measure of community sanitation usage calculated as the proportion of households with a latrine in use. All household members were examined for clinical signs, i.e. trachomatous inflammation, follicular and/or intense, indicative of active trachoma. Multilevel logistic regression was used to estimate prevalence odds ratios (OR) and 95% confidence intervals (CI), adjusting for community, household and individual factors, and to evaluate modification by household latrine use and water access.

Findings

In surveyed areas, prevalence of active trachoma among children was estimated to be 29% (95% CI: 28–30) and mean community sanitation usage was 47% (95% CI: 45–48). Despite significant modification (p < 0.0001), no pattern in stratified ORs was detected. Summarizing across strata, community sanitation usage values of 60 to < 80% and ≥ 80% were associated with lower prevalence odds of active trachoma, compared with community sanitation usage of < 20% (OR: 0.76; 95% CI: 0.57–1.03 and OR: 0.67; 95% CI: 0.48–0.95, respectively).

Conclusion

In Amhara, Ethiopia, a negative correlation was observed between community sanitation usage and prevalence of active trachoma among children, highlighting the need for continued efforts to encourage higher levels of sanitation usage and to support sustained use throughout the community, not simply at the household level.

Population-Based Trachoma Mapping in Six Evaluation Units of Papua New Guinea

PURPOSE

We sought to determine the prevalence of trachomatous inflammation - follicular (TF) in children aged 1-9 years, and trachomatous trichiasis (TT) in those aged ≥15 years, in suspected trachoma-endemic areas of Papua New Guinea (PNG).

METHODS

We carried out six population-based prevalence surveys using the protocol developed as part of the Global Trachoma Mapping Project.

RESULTS

A total of 19,013 individuals were sampled for inclusion, with 15,641 (82.3%) consenting to participate. Four evaluation units had prevalences of TF in children ≥10%, above which threshold the World Health Organization (WHO) recommends mass drug administration (MDA) of azithromycin for at least three years; Western Province (South Fly/Daru) 11.2% (95% confidence interval, CI, 6.9-17.0%), Southern Highlands (East) 12.2% (95% CI 9.6-15.0%), Southern Highlands (West) 11.7% (95% CI 8.5-15.3%), and West New Britain 11.4% (95% CI 8.7-13.9%). TF prevalence was 5.0-9.9% in Madang (9.4%, 95% CI 6.1-13.0%) and National Capital District (6.0%. 95% CI 3.2-9.1%) where consideration of a single round of MDA is warranted. Cases of TT were not found outside West New Britain, in which four cases were seen, generating an estimated population-level prevalence of TT in adults of 0.10% (95% CI 0.00-0.40%) for West New Britain, below the WHO elimination threshold of 0.2% of those aged ≥15 years.

CONCLUSION

Trachoma is a public health issue in PNG. However, other than in West New Britain, there are few data to support the idea that trachoma is a cause of blindness in PNG. Further research is needed to understand the stimulus for the active trachoma phenotype in these populations.

Mathematical Modelling of Trachoma Transmission, Control and Elimination

The World Health Organization has targeted the elimination of blinding trachoma by the year 2020. To this end, the Global Elimination of Blinding Trachoma (GET, 2020) alliance relies on a four-pronged approach, known as the SAFE strategy (S for trichiasis surgery; A for antibiotic treatment; F for facial cleanliness and E for environmental improvement). Well-constructed and parameterized mathematical models provide useful tools that can be used in policy making and forecasting in order to help to control trachoma and understand the feasibility of this large-scale elimination effort. As we approach this goal, the need to understand the transmission dynamics of infection within areas of different endemicities, to optimize available resources and to identify which strategies are the most cost-effective becomes more pressing. In this study, we conducted a review of the modelling literature for trachoma and identified 23 articles that included a mechanistic or statistical model of the transmission, dynamics and/or control of (ocular) Chlamydia trachomatis. Insights into the dynamics of trachoma transmission have been generated through both deterministic and stochastic models. A large body of the modelling work conducted to date has shown that, to varying degrees of effectiveness, antibiotic administration can reduce or interrupt trachoma transmission. However, very little analysis has been conducted to consider the effect of nonpharmaceutical interventions (and particularly the F and E components of the SAFE strategy) in helping to reduce transmission. Furthermore, very few of the models identified in the literature review included a structure that permitted tracking of the prevalence of active disease (in the absence of active infection) and the subsequent progression to disease sequelae (the morbidity associated with trachoma and ultimately the target of GET 2020 goals). This represents a critical gap in the current trachoma modelling literature, which makes it difficult to reliably link infection and disease. In addition, it hinders the application of modelling to assist the public health community in understanding whether trachoma programmes are on track to reach the GET goals by 2020. Another gap identified in this review was that of the 23 articles examined, only one considered the cost-effectiveness of the interventions implemented. We conclude that although good progress has been made towards the development of modelling frameworks for trachoma transmission, key components of disease sequelae representation and economic evaluation of interventions are currently missing from the available literature. We recommend that rapid advances in these areas should be urgently made to ensure that mathematical models for trachoma transmission can robustly guide elimination efforts and quantify progress towards GET 2020.

Multilevel Analysis of Trachomatous Trichiasis and Corneal Opacity in Nigeria: The Role of Environmental and Climatic Risk Factors on the Distribution of Disease

The distribution of trachoma in Nigeria is spatially heterogeneous, with large-scale trends observed across the country and more local variation within areas. Relative contributions of individual and cluster-level risk factors to the geographic distribution of disease remain largely unknown. The primary aim of this analysis is to assess the relationship between climatic factors and trachomatous trichiasis (TT) and/or corneal opacity (CO) due to trachoma in Nigeria, while accounting for the effects of individual risk factors and spatial correlation. In addition, we explore the relative importance of variation in the risk of trichiasis and/or corneal opacity (TT/CO) at different levels. Data from the 2007 National Blindness and Visual Impairment Survey were used for this analysis, which included a nationally representative sample of adults aged 40 years and above. Complete data were available from 304 clusters selected using a multi-stage stratified cluster-random sampling strategy. All participants (13,543 individuals) were interviewed and examined by an ophthalmologist for the presence or absence of TT and CO. In addition to field-collected data, remotely sensed climatic data were extracted for each cluster and used to fit Bayesian hierarchical logistic models to disease outcome. The risk of TT/CO was associated with factors at both the individual and cluster levels, with approximately 14% of the total variation attributed to the cluster level. Beyond established individual risk factors (age, gender and occupation), there was strong evidence that environmental/climatic factors at the cluster-level (lower precipitation, higher land surface temperature, higher mean annual temperature and rural classification) were also associated with a greater risk of TT/CO. This study establishes the importance of large-scale risk factors in the geographical distribution of TT/CO in Nigeria, supporting anecdotal evidence that environmental conditions are associated with increased risk in this context and highlighting their potential use in improving estimates of disease burden at large scales.

Trichiasis (TT) and corneal opacity (CO) are chronic stages of trachoma, which remains an important cause of blindness. This study used multilevel spatial models to investigate risk factors for TT/CO in Nigeria, including data for more than 13,500 adults aged 40 years and above collected in the 2007 National Blindness and Visual Impairment survey. Individual-level risk factors were consistent with those identified in other studies, including a higher risk in females, older individuals and those with lower socioeconomic status. After controlling for these factors, there was evidence that a number of environmental and climatic factors are associated with the distribution of TT/CO in Nigeria. These findings establish for the Nigerian context the importance of risk factors at different scales for the later stages of trachoma, supporting anecdotal evidence that hotter, drier environmental conditions are associated with increased risk.

Control of trachoma in Australia: a model based evaluation of current interventions

BACKGROUND

Australia is the only high-income country in which endemic trachoma persists. In response, the Australian Government has recently invested heavily towards the nationwide control of the disease.

METHODOLOGY/PRINCIPAL FINDINGS

A novel simulation model was developed to reflect the trachoma epidemic in Australian Aboriginal communities. The model, which incorporates demographic, migration, mixing, and biological heterogeneities, was used to evaluate recent intervention measures against counterfactual past scenarios, and also to assess the potential impact of a series of hypothesized future intervention measures relative to the current national strategy and intensity. The model simulations indicate that, under the current intervention strategy and intensity, the likelihood of controlling trachoma to less than 5% prevalence among 5-9 year-old children in hyperendemic communities by 2020 is 31% (19%-43%). By shifting intervention priorities such that large increases in the facial cleanliness of children are observed, this likelihood of controlling trachoma in hyperendemic communities is increased to 64% (53%-76%). The most effective intervention strategy incorporated large-scale antibiotic distribution programs whilst attaining ambitious yet feasible screening, treatment, facial cleanliness and housing construction targets. Accordingly, the estimated likelihood of controlling trachoma in these communities is increased to 86% (76%-95%).

CONCLUSIONS/SIGNIFICANCE

Maintaining the current intervention strategy and intensity is unlikely to be sufficient to control trachoma across Australia by 2020. However, by shifting the intervention strategy and increasing intensity, the likelihood of controlling trachoma nationwide can be significantly increased.

The niche reduction approach: an opportunity for optimal control of infectious diseases in low-income countries?

BACKGROUND

During the last century, WHO led public health interventions that resulted in spectacular achievements such as the worldwide eradication of smallpox and the elimination of malaria from the Western world. However, besides major successes achieved worldwide in infectious diseases control, most elimination/control programs remain frustrating in many tropical countries where specific biological and socio-economical features prevented implementation of disease control over broad spatial and temporal scales. Emblematic examples include malaria, yellow fever, measles and HIV. There is consequently an urgent need to develop affordable and sustainable disease control strategies that can target the core of infectious diseases transmission in highly endemic areas.

DISCUSSION

Meanwhile, although most pathogens appear so difficult to eradicate, it is surprising to realize that human activities are major drivers of the current high rate of extinction among upper organisms through alteration of their ecology and evolution, i.e., their "niche". During the last decades, the accumulation of ecological and evolutionary studies focused on infectious diseases has shown that the niche of a pathogen holds more dimensions than just the immune system targeted by vaccination and treatment. Indeed, it is situated at various intra- and inter- host levels involved on very different spatial and temporal scales. After developing a precise definition of the niche of a pathogen, we detail how major advances in the field of ecology and evolutionary biology of infectious diseases can enlighten the planning and implementation of infectious diseases control in tropical countries with challenging economic constraints.

SUMMARY

We develop how the approach could translate into applied cases, explore its expected benefits and constraints, and we conclude on the necessity of such approach for pathogen control in low-income countries.

The association between latrine use and trachoma: a secondary cohort analysis from a randomized clinical trial

Latrine use has been promoted as a component of an integrated strategy for trachoma control. As part of a randomized trial in Ethiopia, 12 communities received a mass azithromycin distribution followed by a latrine promotion intervention. A random sample of children ages 0-9 years in each community was monitored longitudinally for ocular chlamydia. After latrine construction ended, those communities with a higher proportion of households using latrines were more likely to experience a reduction in the prevalence of ocular chlamydia. Specifically, for each 10% increase in latrine use, there was a 2.0% decrease (95% confidence interval = 0.2-3.9% decrease) in the community prevalence of ocular chlamydia over the subsequent year (P = 0.04).

The added value of water, sanitation, and hygiene interventions to mass drug administration for reducing the prevalence of trachoma: a systematic review examining

Trachoma is the leading cause of infectious blindness worldwide. The SAFE strategy, the World Health Organization-recommended method to eliminate blinding trachoma, combines developments in water, sanitation, surgery, and antibiotic treatment. Current literature does not focus on the comprehensive effect these components have on one another. The present systematic review analyzes the added benefit of water, sanitation, and hygiene education interventions to preventive mass drug administration of azithromycin for trachoma. Trials were identified from the PubMed database using a series of search terms. Three studies met the complete criteria for inclusion. Though all studies found a significant change in reduction of active trachoma prevalence, the research is still too limited to suggest the impact of the “F” and “E” components on trachoma prevalence and ultimately its effects on blindness.

Enhancing community knowledge and health behaviors to eliminate blinding trachoma in Mali using radio messaging as a strategy

The National Blindness Prevention Program in Mali has broadcast messages on the radio about trachoma as part of the country's trachoma elimination strategy since 2008. In 2011, a radio impact survey using multi-stage cluster sampling was conducted in the regions of Kayes and Segou to assess radio listening habits, coverage of the broadcasts, community knowledge and behavior specific to trachoma and facial cleanliness of children. Radio access and listening were high, with 60% of respondents having heard a message on the radio about trachoma. The majority of respondents knew about trachoma, its root causes, its impact on health and prevention measures. Additionally, 66% reported washing their children's faces more than or equal to twice/day and 94% reported latrine disposal of feces. A high percentage of persons who gave a positive response to knowledge and behavior questions reported hearing the trachoma messages on the radio with 60% reporting that the radio is where they learned about trachoma. There was no significant difference in facial cleanliness when comparing children whose primary caregiver had/had not heard the trachoma messages. Next steps include revising the current messages to include more focused behavior change messaging and to engage in a more robust use of community radios.

Three-year outcomes of the surgery for trichiasis, antibiotics to prevent recurrence trial

OBJECTIVE

To determine whether treatment with oral azithromycin compared with topical tetracycline reduces the recurrence of trichiasis for up to 3 years following surgery for trichiasis.

METHODS

The Surgery for Trichiasis, Antibiotics to Prevent Recurrence (STAR) trial is a randomized, single-masked, clinical trial conducted in southern Ethiopia, a region where trachoma is hyperendemic. A total of 1452 patients who underwent trichiasis surgery were randomly assigned at a 2:1 ratio to either a single dose of oral azithromycin (1 g) or topical tetracycline (twice per day for 6 weeks) following surgery.

MAIN OUTCOME MEASURES

Recurrence of trichiasis within 3 years following surgery.

RESULTS

The rate of recurrence was 10% in the azithromycin group and 13% in the tetracycline group. The azithromycin group had a 22% reduction in recurrence of trichiasis 3 years after surgery compared with the tetracycline group (P = .13). Severity of entropion at baseline was the most significant predictor of recurrence of trichiasis at 3 years.

CONCLUSION

Trichiasis recurrence rates in the STAR trial remained low for up to 3 years following surgery. The protective effect of a single dose of azithromycin was less than at 1 year and, although not statistically significant, was still suggestive up to 3 years following trichiasis surgery.

APPLICATION TO CLINICAL PRACTICE

A single dose of azithromycin after surgery remains an integral component of the World Health Organization's strategy for the elimination of trachoma by the year 2020.

Relationship between distance to social gathering facilities and risk of trachoma for households in rural Tanzanian communities

Few studies have examined the physical isolation of households with trachoma cases. Thus, in this study, we sought to examine the association between household isolation, as measured by distance to social gathering facilities, and risk of trachoma. We hypothesized that households located closer to such facilities would have a decreased risk of trachoma, due to a variety of social, economic, and cultural reasons. To test this hypothesis we conducted a case-control study of 668 households (93 cases, 575 controls) in eight villages in Kongwa District, Tanzania, in 2007. Case households were defined as having a child aged 1-5 years with clinical signs of trachoma. Distance of household's place of residence to three main social gathering facilities - bars/cafés, religious establishments, and commercial/government center - was measured with a portable geographic positioning system. Multiple logistic regression analyses, which controlled for potential confounders and accounted for clustering, demonstrated increased risk of trachoma with increasing distance to social gathering facilities. Compared with distances of ≤700 m, odds of trachoma were approximately two-fold higher for households living >1400 m from bars/cafés and from religious establishments, suggesting increased risk of trachoma for households at the fringes of communities. Targeting these isolated households with special programming along with dissemination through trusted social gathering facilities may improve effectiveness of current prevention efforts.

Control of neglected tropical diseases needs a long-term commitment

BACKGROUND

Neglected tropical diseases are widespread, particularly in sub-Saharan Africa, affecting over 2 billion individuals. Control of these diseases has gathered pace in recent years, with increased levels of funding from a number of governmental or non-governmental donors. Focus has currently been on five major 'tool-ready' neglected tropical diseases (lymphatic filariasis, onchocerciasis, schistosomiasis, soil-transmitted helminthiasis and trachoma), using a package of integrated drug delivery according to the World Health Organization guidelines for preventive chemotherapy.

DISCUSSION

Success in controlling these neglected tropical diseases has been achieved in a number of countries in recent history. Experience from these successes suggests that long-term sustainable control of these diseases requires: (1) a long-term commitment from a wider range of donors and from governments of endemic countries; (2) close partnerships of donors, World Health Organization, pharmaceutical industries, governments of endemic countries, communities, and non-governmental developmental organisations; (3) concerted action from more donor countries to provide the necessary funds, and from the endemic countries to work together to prevent cross-border disease transmission; (4) comprehensive control measures for certain diseases; and (5) strengthened primary healthcare systems as platforms for the national control programmes and capacity building through implementation of the programmes.

CONCLUSIONS

The current level of funding for the control of neglected tropical diseases has never been seen before, but it is still not enough to scale up to the 2 billion people in all endemic countries. While more donors are sought, the stakeholders must work in a coordinated and harmonised way to identify the priority areas and the best delivery approaches to use the current funds to the maximum effect. Case management and other necessary control measures should be supported through the current major funding streams in order to achieve the objectives of the control of these diseases. For a long-term and sustainable effort, control of neglected tropical diseases should also be integrated into national primary healthcare systems.

Eradicating blinding trachoma: What is working?

Trachoma remains the leading cause of preventable corneal blindness in developing countries. The disease is contracted in early childhood by repeated infection of the ocular surface by C. trachomatis. Initial clinical manifestation is a follicular conjunctivitis which if not treated on timely basis, may lead to conjunctival and eyelid scarring that may eventually result in corneal scarring and loss of vision. Over the past two decades, a remarkable reduction in the prevalence of active trachoma has occurred due to the World Health Organization's (WHOs) program GET 2020 for the elimination of trachoma with adoption of the SAFE strategy incorporating Surgery, Antibiotic treatment, Facial cleanliness and Environmental hygiene. However, patients who already had infection at young age may present with adnexal-related complications of trachomatous scarring that may cause corneal scarring and visual loss. These patients may present with evidence of trichiasis/entropion as well as eyelid retraction. Lacrimal complications may include nasolacrimal-duct obstruction, dacryocystitis and canaliculitis requiring intervention. In addition to the increased risk for corneal scarring, trichiasis/entropion may further increase the risks for microbial keratitis in patients who may have unrecognized dacryocystitis and canaliculitis. Female patients may have more trachomtous-related complications and may present at an early age. Available evidence indicates that SAFE strategy may be effective and on the right track towards achieving GET 2020 goal for the eradication of trachoma.

Evaluating a school-based trachoma curriculum in Tanzania

Trachoma remains a public health problem in a number of sub-Saharan Africa countries; behavioral change and environmental improvements are cornerstones of prevention efforts. Evidence of successful health education are few in Africa. Health education efforts through primary schools have recently been developed and adopted in Tanzania. We evaluated changes from 2004 to 2005 in knowledge and reported behavioral change as well as nasal and ocular discharge and clean faces in selected schools in central Tanzania. This was a mixed-methods study involving both schoolchildren and school teachers. We found a significant reduction in nasal discharge (from 4.5% to 0.5%) and dirty faces (from 3.6% to 0.9%) and improvements in some knowledge- and behavior-related indices by primary schoolchildren in the intervention villages. The teachers viewed the trachoma curriculum positively but reported that the lack of water at the schools limited application of the health education messages. The disparity between health education messages and environmental capacities for implementing these messages (no wells at the schools and minimal latrine facilities at the schools and homes) limited usefulness of the curriculum.

The Johns Hopkins Center for Global Health: transcending borders for world health

The causes and effects of many health problems, whether infectious, environmental, lifestyle related, or caused by manmade or natural disasters, are becoming increasingly global in nature. Integrated approaches to solving these problems require the expertise of large and diverse groups of health professionals, to design lifesaving research and to implement effective responses. The Johns Hopkins University public health, medical, and nursing communities have a history of leadership in both modern medicine and public health, and they have unparalleled human resources in the clinical, research, programmatic, policy, and educational domains, with an extensive network of international colleagues and collaborators. To best utilize these resources to have a positive impact on global health issues, the university created the Center for Global Health in 2006 to facilitate and coordinate the various international activities of the faculty and students in the field of global health. The center has seven specific initiatives aimed at educating students and facilitating the faculty's collaborative research: serving as a resource center for global health activities within the university; facilitating and coordinating topical areas of global research; promoting educational programs in global health; providing global health field training grants; granting global health scholarships; focusing on global health research and practice; and coordinating symposia, forums, and policy initiatives. The author elaborates on these initiatives and discusses challenges experienced in establishing the center, as well as evaluation methods for determining the center's success.

Multiple Chlamydiaceae species in trachoma: implications for disease pathogenesis and control

BACKGROUND

Chlamydia trachomatis is a unique obligate intracellular bacterium that remains the leading cause of sexually transmitted bacterial diseases and preventable blindness worldwide. Chronic ocular infections are referred to as trachoma, and predominate in developing countries. Since 2001, the World Health Organization has promoted control strategies including antibiotics, improved hygiene, and environmental measures with limited success. Consequently, a vaccine is urgently needed. Integral to vaccine design is an understanding of the interactions of the pathogen and host immune response. Various animal models of trachoma show that urogenital C. trachomatis strains and other species of the family Chlamydiaceae produce severe conjunctival inflammation and scarring similar to that of the ocular C. trachomatis strains. However, we do not know the extent of organisms that may be involved in human trachoma. Furthermore, C. trachomatis heat shock protein 60 (Hsp60) has been implicated in inflammation and conjunctival scarring but the role of other Chlamydiaceae Hsp60 in disease pathogenesis has not been examined. In this study, we set out to identify whether other Chlamydiaceae species are present in trachoma, and determine their association with severity of clinical disease and with mucosal and systemic immune responses to Chlamydiaceae species-specific Hsp60 to further investigate the immunopathogenesis of this blinding disease.

METHODS AND FINDINGS

We randomly selected nine of 49 households in a trachoma-endemic region of Nepal. Trachoma was graded, and real-time, quantitative (k)PCR was used to detect genomic DNA and cDNA (from RNA) for Chlamydiaceae ompA and 16S rRNA genes, respectively, from conjunctival swabs. IgG antibody responses to recombinant (r) Chlamydiaceae species-specific Hsp60 were determined for tears and sera. Surprisingly, all three species-C. trachomatis, Chlamydophila psittaci, and Chlamydophila pneumoniae-were detected in eight (89%) study households; one household had no members infected with C. pneumoniae. Of 80 (63%; n = 127) infected individuals, 28 (35%) had infection with C. psittaci, or C. pneumoniae, or both; single and dual infections with C. psittaci and C. pneumoniae were significantly associated with severe conjunctival inflammation (OR 4.25 [95% confidence interval (CI), 2.9-11.3], p = 0.009] as were single infections with C. trachomatis (OR 5.7 [95% CI, 3.8-10.1], p = 0.002). Of the 80 infected individuals, 75 (93.8%) were also positive for 16S rRNA by kPCR for the same organism identified by ompA. Individuals with tear IgG immunoreactivity to Chlamydiaceae rHsp60 were eight times more likely than individuals without tear immunoreactivity to be infected (95% CI 6.4-15.1; p = 0.003), 6.2 times more likely to have severe inflammation (95% CI 4.4-12.6; p = 0.001), and 5.7 times more likely to have scarring (95% CI 3.9-11.1; p = 0.019) while individuals with serum IgG immunoreactivity were 4.1 times more likely to be infected (95% CI 3.1-10.1; p = 0.014).

CONCLUSIONS

We provide substantial evidence for the involvement of C. psittaci and C. pneumoniae, in addition to C. trachomatis, in trachoma. The distribution of Chlamydiaceae species by household and age suggests that these infections are widespread and not just sporadic occurrences. Infection with multiple species may explain the failure to detect chlamydiae among active trachoma cases, when only C. trachomatis is assayed for, and the failure of clinically active cases to resolve their disease following what would be considered effective C. trachomatis treatment. The evidence for viable (RNA-positive) organisms of all three species in single and coinfections, the significant association of these infections with severe inflammation, and the significant association of tear and serum IgG responses to Chlamydiaceae Hsp60 with inflammation and scarring, support the role of all three species in disease pathogenesis. Thus, while our findings should be confirmed in other trachoma-endemic countries, our data suggest that a reevaluation of treatment regimens and vaccine design may be required. Understanding the full impact of Chlamydiaceae species on the epidemiology, immunopathology, and disease outcome of trachoma presents a new challenge for Chlamydiaceae research.

An eye for inequality: how trachoma relates to poverty in Tanzania and Vietnam

PURPOSE

An important challenge for trachoma control strategies is to break the circle of poverty, poor hygiene and poor health by bringing its benefits to the poor. This article aims to assess to what extent trachoma is a disease of the poor, and trachoma services reach the poor in Tanzania and Vietnam.

METHODS

Individual level data on trachoma prevalence (active trachoma and trichiasis) and utilization of trachoma-related services were collected in both countries in 2004. Prevalence data were also available for Vietnam in 2001. We used household level data to construct an asset index as our living standards measure. Next, we related trachoma prevalence and service use to living standards, and used concentration indices to summarize and test the degree of inequality.

RESULTS

Trachoma prevalence was higher among the poorest groups in Tanzania. No such relation could be established in Vietnam where prevalence declined over the period 2001-2004 and particularly so among the least poor. Antibiotics were used more by the poorest in Tanzania and by the less poor in Vietnam. In both countries, there was no unequivocal pattern for the relation between living standards and the use of trachoma services.

CONCLUSIONS

Trachoma is found to be a disease of the poorest in Tanzania, but not in Vietnam. In the latter country there are indications that district characteristics have an important impact on trachoma prevalence. The higher use of antibiotics among the better-off in Vietnam may have contributed to their larger decline in active trachoma prevalence between 2001 and 2004 compared to the poorer segments.

Clinical and microbiological diagnosis of trachoma in children living in rural areas in the district of Attock, Punjab, Pakistan

BACKGROUND

Trachoma is a sight-threatening process triggered by infection of the conjunctiva with Chlamydiae. When this infection becomes chronic and is associated with poverty it triggers trachoma, the prime cause of infectious blindness in the world. Since the 1958 report indicating that the highest incidence of trachoma in Pakistan was found in the province of Punjab, no new trials have been published. In the present study, we assessed the prevalence of trachoma in 3968 children living in 11 rural villages in the district of Attock, Punjab, Pakistan. The children with trachoma were sampled to detect C. trachomatis by PCR.

METHODS

Children in rural villages in the district of Attock were examined for trachoma in February 2004. Samples were obtained by scraping, and DNA was extracted (MagnaPure-LC Robot) and amplified to detect C. trachomatis (Amplicor-Roche). The quality of sampling was assessed by quantifying the number of cells by real-time PCR.

RESULTS

The prevalence of trachoma was 3.7% (0 to 6.2%). PCR was positive in 20% of samples from trachomatous children and the number of cells was always > 100/sample. The income levels, illiteracy, use of latrines, water supply, and the presence of animals close to dwellings were similar in all the villages. In Sujjenda, the prevalence was doubled in the warmest season.

CONCLUSIONS

Trachoma was diagnosed in 3.7% of the children aged < 10 years. The low rates for positive PCR may be due to loss of the plasmid, the involvement of other Chlamydiae, or their absence in chronic infections. The results obtained here underestimate the prevalence of trachoma because most of the mothers (and babies) were not tested in the district of Attock.

Surgery for trachomatous trichiasis: findings from a survey of trichiasis surgeons in Tanzania

AIMS

To measure the productivity and factors associated with high productivity of trichiasis surgeons.

METHODS

A standardised, pretested questionnaire was posted to all trichiasis surgeons trained in Tanzania at the address listed at the time of training, and then followed up by post and telephone with those who did not return the form. Questions asked related to place of work, number of surgeries carried out, supplies and equipment available, and outreach activities. A random selection of high-productivity and low-productivity surgeons was invited to a focus group meeting to discuss factors that affected productivity.

RESULTS

28 of the trained surgeons had died, retired or could not be located. Forms were retrieved from 95 others. Productivity (averaged over the past 4 years) was low overall, but highly variable. The mean number of surgeries per year was 22.3 (SD 48.1) and the median was 7. The most important factor associated with higher productivity was conducting outreach activities. Conducting outreach was associated with having a complete set of instruments and consumables and with being able to identify a supervisor.

CONCLUSIONS

Redesigning the provision of trichiasis surgery (in particular, supervision, support and community programmes/outreach) is necessary to ensure that the investment from training is used adequately.

[Factors associated with trachoma in a low-endemic area in southeast Brazil]

A case-control study matched by age and school (n=121 pairs) was carried out among pre-elementary and elementary students from low-income families living in Greater Metropolitan São Paulo, Brazil, with the objective of investigating factors associated with trachoma in a low prevalence area. The case definition for trachoma was that proposed by the World Health Organization. The dependent variable was trachoma and the independent variables were social stratum, housing of migrants from endemic areas, facial hygiene habits, head of family's schooling, access to potable water, contact with another case in the family, and slum residence. Unadjusted and adjusted odds ratios (OR), with their respective 95% confidence intervals (95%CI), were estimated by conditional logistic regression. In the multivariate analysis, belonging to the poorest social stratum (OR = 8.21; 95%CI: 1.50-44.81), housing people from endemic areas (OR = 2.44; 95%CI: 1.10-5.46), contact with another case in the family (OR = 2.52; 95%CI: 0.98-6.48), and facial hygiene habits (OR = 0.50; 95%CI: 0.26-0.98) were independently associated with trachoma.

Analysis of incidence rates in cluster-randomized trials of interventions against recurrent infections, with an application to trachoma

A method is developed for the Bayesian analysis of rate ratios of repeated events in matched cluster-randomized trials, and applied to the Flies and Eyes trial against trachoma in The Gambia. A non-mechanistic analysis estimates the incidence rate ratio for insecticide spray, relative to no intervention, as 0.59 (95 per cent credible interval 0.37--0.92), and for latrine provision as 0.67 (0.41--1.01). The method also yields incidence and clearance rate ratios for age. In the Flies and Eyes trial, the former rates are estimated to decrease with age, although no clear pattern is seen in the latter. Using clinical active trachoma as a marker of infection, and net catches to measure fly density, a mechanistic model is developed to estimate the proportion of transmission due to flies. However, it was not possible to estimate this proportion accurately, and a lack of association was noted between the magnitudes of reductions in fly density and in trachoma. The lack of knowledge on the relative importance of different transmission routes is a constraint on the current global programme for the elimination of trachoma.