Cholera Rapid Test with Enrichment Step Has Diagnostic Performance Equivalent to Culture

Cholera rages in Africa and the Middle East: A narrative review on challenges and solutions

Background and Aim

Cholera is a life-threatening infectious disease that is still one of the most common acute watery diarrheal diseases in the world today. Acute diarrhea and severe dehydration brought on by cholera can cause hypovolemic shock, which can be fatal in minutes. Without competent clinical therapy, the rate of case fatality surpasses 50%. The purpose of this review was to highlight cholera challenges in Africa and the Middle East and explain the reasons for why this region is currently a fertile environment for cholera. We investigated cholera serology, epidemiology, and the geographical distribution of cholera in Africa and the Middle East in 2022 and 2023. We reviewed detection methods, such as rapid diagnostic tests (RDTs), and treatments, such as antibiotics and phage therapy. Finally, this review explored oral cholera vaccines (OCVs), and the vaccine shortage crisis.

Methods

We carried out a systematic search in multiple databases, including PubMed, Web of Science, Google Scholar, Scopus, MEDLINE, and Embase, for studies on cholera using the following keywords: ((Cholera) OR (Vibrio cholera) and (Coronavirus) OR (COVID-19) OR (SARS-CoV2) OR (The Middle East) OR (Africa)).

Results and Conclusions

Cholera outbreaks have increased dramatically, mainly in Africa and many Middle Eastern countries. The COVID-19 pandemic has reduced the attention devoted to cholera and disrupted diagnosis and treatment services, as well as vaccination initiatives. Most of the cholera cases in Africa and the Middle East were reported in Malawi and Syria, respectively, in 2022. RDTs are effective in the early detection of cholera epidemics, especially with limited advanced resources, which is the case in much of Africa. By offering both direct and indirect protection, expanding the use of OCV will significantly reduce the burden of current cholera outbreaks in Africa and the Middle East.

Review of Rapid Diagnostic Methods for Vibrio Cholerae Detection in the Last Decade (2011-2022)

Introduction

Cholera epidemic poses a global public health threat, heavily impacting the global economy and societies, with Africa and Asia particularly affected due to factors like; inadequate sanitation, contaminated water, and overcrowding. The associated high rates of morbidity and mortality strain productivity and healthcare costs while complicating control measures. Consequently, the World Health Organization's cholera control initiative and the Diarrhoeal Diseases Laboratory Network advocate for rapid responses to outbreaks and continuous environmental surveillance, since traditional cholera detection methods relying on phenotypic fingerprinting, although considered the gold standard, suffer from labour-intensiveness, time-consumption, and skill requirements. This results in inadequate surveillance and delayed treatment in remote areas lacking well-equipped laboratories.

Methods

A systematic review was conducted to evaluate the development and performance of cholera rapid diagnostic techniques for detecting cholera in clinical samples and for environmental surveillance purposes over the past decade.

Results

Twenty-four commercially produced diagnostics were identified in January 2011. Ten more were mentioned in the literature and yet did not provide enough relevant data due to suspected production withdrawal or fall-back. The vast bulk of tests were discovered to be based on antigen or antibody detection, with DNA accounting for a large proportion of the residual tests. This study revealed a plethora of diagnostic methods, some of which have not yet made it to the commercial market. Promising approaches, such as; Loop-mediated isothermal amplification (LAMP), ELISA, and simplified PCR protocols, are likely to play a significant role in future cholera screening. Findings are herein summarised in tables and figures.

Conclusion

Cholera epidemic continues to present a formidable global health challenge with economic and social repercussions. Traditional detection methods fall short in resource-limited areas, necessitating the exploration of advanced molecular techniques, like aptamers, to improve diagnosis, surveillance, and control measures, especially in regions vulnerable to cholera outbreaks.

Estimating the proportion of clinically suspected cholera cases that are true Vibrio cholerae infections: A systematic review and meta-analysis

BACKGROUND

Cholera surveillance relies on clinical diagnosis of acute watery diarrhea. Suspected cholera case definitions have high sensitivity but low specificity, challenging our ability to characterize cholera burden and epidemiology. Our objective was to estimate the proportion of clinically suspected cholera that are true Vibrio cholerae infections and identify factors that explain variation in positivity.

METHODS AND FINDINGS

We conducted a systematic review of studies that tested ≥10 suspected cholera cases for V. cholerae O1/O139 using culture, PCR, and/or a rapid diagnostic test. We searched PubMed, Embase, Scopus, and Google Scholar for studies that sampled at least one suspected case between January 1, 2000 and April 19, 2023, to reflect contemporary patterns in V. cholerae positivity. We estimated diagnostic test sensitivity and specificity using a latent class meta-analysis. We estimated V. cholerae positivity using a random-effects meta-analysis, adjusting for test performance. We included 119 studies from 30 countries. V. cholerae positivity was lower in studies with representative sampling and in studies that set minimum ages in suspected case definitions. After adjusting for test performance, on average, 52% (95% credible interval (CrI): 24%, 80%) of suspected cases represented true V. cholerae infections. After adjusting for test performance and study methodology, the odds of a suspected case having a true infection were 5.71 (odds ratio 95% CrI: 1.53, 15.43) times higher when surveillance was initiated in response to an outbreak than in non-outbreak settings. Variation across studies was high, and a limitation of our approach was that we were unable to explain all the heterogeneity with study-level attributes, including diagnostic test used, setting, and case definitions.

CONCLUSIONS

In this study, we found that burden estimates based on suspected cases alone may overestimate the incidence of medically attended cholera by 2-fold. However, accounting for cases missed by traditional clinical surveillance is key to unbiased cholera burden estimates. Given the substantial variability in positivity between settings, extrapolations from suspected to confirmed cases, which is necessary to estimate cholera incidence rates without exhaustive testing, should be based on local data.

Drivers of the dynamics of the spread of cholera in the Democratic Republic of the Congo, 2000-2018: An eco-epidemiological study

BACKGROUND

The dynamics of the spread of cholera epidemics in the Democratic Republic of the Congo (DRC), from east to west and within western DRC, have been extensively studied. However, the drivers of these spread processes remain unclear. We therefore sought to better understand the factors associated with these spread dynamics and their potential underlying mechanisms.

METHODS

In this eco-epidemiological study, we focused on the spread processes of cholera epidemics originating from the shores of Lake Kivu, involving the areas bordering Lake Kivu, the areas surrounding the lake areas, and the areas out of endemic eastern DRC (eastern and western non-endemic provinces). Over the period 2000-2018, we collected data on suspected cholera cases, and a set of several variables including types of conflicts, the number of internally displaced persons (IDPs), population density, transportation network density, and accessibility indicators. Using multivariate ordinal logistic regression models, we identified factors associated with the spread of cholera outside the endemic eastern DRC. We performed multivariate Vector Auto Regressive models to analyze potential underlying mechanisms involving the factors associated with these spread dynamics. Finally, we classified the affected health zones using hierarchical ascendant classification based on principal component analysis (PCA).

FINDINGS

The increase in the number of suspected cholera cases, the exacerbation of conflict events, and the number of IDPs in eastern endemic areas were associated with an increased risk of cholera spreading outside the endemic eastern provinces. We found that the increase in suspected cholera cases was influenced by the increase in battles at lag of 4 weeks, which were influenced by the violence against civilians with a 1-week lag. The violent conflict events influenced the increase in the number of IDPs 4 to 6 weeks later. Other influences and uni- or bidirectional causal links were observed between violent and non-violent conflicts, and between conflicts and IDPs. Hierarchical clustering on PCA identified three categories of affected health zones: densely populated urban areas with few but large and longer epidemics; moderately and accessible areas with more but small epidemics; less populated and less accessible areas with more and larger epidemics.

CONCLUSION

Our findings argue for monitoring conflict dynamics to predict the risk of geographic expansion of cholera in the DRC. They also suggest areas where interventions should be appropriately focused to build their resilience to the disease.

Poor Sensitivity of Stool Culture Compared to Polymerase Chain Reaction in Surveillance for Vibrio cholerae in Haiti, 2018-2019

We report on the sensitivity and specificity of stool culture compared to polymerase chain reaction for detecting Vibrio cholerae in Haiti during the waning period of the initial outbreak in 2018-2019. We found that stool culture (with a sensitivity of 33.3% and specificity of 97.4%) may not be sufficiently robust in this context.

Implementation of targeted cholera response activities, Cameroon

Objective

To describe the implementation of case-area targeted interventions to reduce cholera transmission using a rapid, localized response in Kribi district, Cameroon.

Methods

We used a cross-sectional design to study the implementation of case-area targeted interventions. We initiated interventions after rapid diagnostic test confirmation of a case of cholera. We targeted households within a 100-250 metre perimeter around the index case (spatial targeting). The interventions package included: health promotion, oral cholera vaccination, antibiotic chemoprophylaxis for nonimmunized direct contacts, point-of-use water treatment and active case-finding.

Findings

We implemented eight targeted intervention packages in four health areas of Kribi between 17 September 2020 and 16 October 2020. We visited 1533 households (range: 7-544 per case-area) hosting 5877 individuals (range: 7-1687 per case-area). The average time from detection of the index case to implementation of interventions was 3.4 days (range: 1-7). Oral cholera vaccination increased overall immunization coverage in Kribi from 49.2% (2771/5621 people) to 79.3% (4456/5621 people). Interventions also led to the detection and prompt management of eight suspected cases of cholera, five of whom had severe dehydration. Stool culture was positive for Vibrio cholerae O1 in four cases. The average time from onset of symptoms to admission of a person with cholera to a health facility was 1.2 days.

Conclusion

Despite challenges, we successfully implemented targeted interventions at the tail-end of a cholera epidemic, after which no further cases were reported in Kribi up until week 49 of 2021. The effectiveness of case-area targeted interventions in stopping or reducing cholera transmission needs further investigation.

Development of a simple, rapid, and sensitive molecular diagnostic assay for cholera

Cholera continues to inflict high rates of morbidity and mortality. Prompt identification of cholera cases facilitates rapid outbreak responses in the short term while providing reliable surveillance data to guide long-term policies and interventions. Microbiological stool culture, the current recognized gold standard for diagnosing cholera, has significant limitations. Rapid diagnostic tests (RDTs) represent promising alternatives for diagnosing cholera in areas with limited laboratory infrastructure. However, studies conducted with the current cholera RDTs demonstrated wide variations in sensitivity and specificity. To address this gap in the diagnosis of cholera, we developed a simple, rapid, and sensitive diagnostic assay, "Rapid LAMP based Diagnostic Test (RLDT)." With a novel, simple sample preparation method directly from the fecal samples along with lyophilized reaction strips and using established Loop-mediated Isothermal Amplification (LAMP) platform, cholera toxin gene (ctxA) and O1 (O1rfb) gene could be detected in less than an hour. Cholera RLDT assay is cold chain and electricity-free. To avoid any end-user bias, a battery-operated, handheld reader was used to read the RLDT results. The performance specifications of the cholera RLDT assay, including analytical sensitivity and specificity, were evaluated using direct fecal samples, dried fecal samples on filter paper, and environmental water samples spiked with cholera strain. The limit of detection (LOD) was ~104 CFU/gm of stool for both ctxA and O1 genes, corresponding to about 1 CFU of Vibrio cholerae per reaction within 40 minutes. The LOD was 10 bacteria per ml of environmental water when tested with RLDT directly, without enrichment. Being simple, RLDT has the potential to be applied in resource-poor endemic settings for rapid, sensitive, and reliable diagnosis of cholera.

Knowledge, Attitude, and Practice in a Sample of the Lebanese Population Regarding Cholera

The evaluation of knowledge, attitude, and practices towards an emerging disease is an essential component of public health preventive measures during an outbreak. In October 2022, an outbreak of cholera was reported in Lebanon, which is the first to be reported in the Middle Eastern country for 30 years. This study aimed to explore the level of knowledge as well as attitude and practice of the general public in Lebanon towards cholera. A self-administered structured questionnaire was distributed via an online link to individuals living in Lebanon during October-November 2022. The survey instrument comprised items to assess the sociodemographic data; questions on knowledge about cholera symptoms, transmission, and prevention; as well as attitude and practice questions. Our study involved 553 participants, with a median age of 24 years and a majority of females (72.5%). The results showed that the majority of respondents correctly identified diarrhea as a symptom of cholera and recognized the spread via contaminated water and food. Having a university level education compared with secondary school or less (adjusted odds ratio (aOR) = 2.09), being married compared with single (aOR = 1.67), and working in the medical field compared with unemployed (aOR = 4.19) were significantly associated with higher odds of having good cholera knowledge. Having good knowledge compared with having a poor level of cholera knowledge (aOR = 1.83) and older age (aOR = 1.03) were significantly associated with higher odds of having a good attitude towards cholera. The current study showed an overall high knowledge score on cholera among the Lebanese population. Nevertheless, gaps in cholera knowledge were identified and should be addressed, particularly among workers in the medical field. Thus, we recommend targeted health education to the general population that aims to strengthen the health resilience in the community.

Development of a Monoclonal Antibody to a Vibriophage as a Proxy for Vibrio cholerae Detection

Cholera is an acute watery, diarrheal disease that causes high rates of morbidity and mortality without treatment. Early detection of the etiologic agent of toxigenic Vibrio cholerae is important to mobilize treatment and mitigate outbreaks. Monoclonal antibody (mAb) based rapid diagnostic tests (RDTs) enable early detection in settings without laboratory capacity. However, the odds of an RDT testing positive are reduced by nearly 90% when the common virulent bacteriophage ICP1 is present. We hypothesize that adding a mAb for the common, and specific, virulent bacteriophage ICP1 as a proxy for V. cholerae to an RDT will increase diagnostic sensitivity when virulent ICP1 phage is present. In this study, we used an in-silico approach to identify immunogenic ICP1 protein targets that were conserved across disparate time periods and locations. Specificity of targets to cholera patients with known ICP1 was determined, and specific targets were used to produce mAbs in a murine model. Candidate mAbs to the head protein demonstrated specificity to ICP1 by Enzyme linked immunosorbent assay (ELISA) and an ICP1 phage neutralization assay. The limit of detection of the final mAb candidate for ICP1 phage particles spiked into cholera stool matrix was 8 × 10⁵ PFU by Western blotting analysis. This mAb will be incorporated into a RDT prototype for evaluation in a future diagnostic study to test the guiding hypothesis behind this study.

Cholera diagnosis in human stool and detection in water: A systematic review and meta-analysis

Background

Cholera continues to pose a problem for low-resource, fragile and humanitarian contexts. Evidence suggests that 2.86 million cholera cases and 95,000 deaths due to cholera are reported annually. Without quick and effective diagnosis and treatment, case-fatality may be 50%. In line with the priorities of the Global Task Force on Cholera Control, we undertook a systematic review and meta-analysis of diagnostic test accuracy and other test characteristics of current tests for cholera detection in stool and water.

Methods

We searched 11 bibliographic and grey literature databases. Data was extracted on test sensitivity, specificity and other product information. Meta-analyses of sensitivity and specificity were conducted for tests reported in three or more studies. Where fewer studies reported a test, estimates were summarised through narrative synthesis. Risk of Bias was assessed using QUADAS-2.

Results

Searches identified 6,637 records; 41 studies reporting on 28 tests were included. Twenty-two tests had both sensitivities and specificities reported above 95% by at least one study, but there was, overall, wide variation in reported diagnostic accuracy across studies. For the three tests where meta-analyses were possible the highest sensitivity meta-estimate was found in the Cholera Screen test (98.6%, CI: 94.7%-99.7%) and the highest specificity meta-estimate in the Crystal VC on enriched samples (98.3%, CI: 92.8%-99.6%). There was a general lack of evidence regarding field use of tests, but where presented this indicated trends for lower diagnostic accuracy in field settings, with lesser-trained staff, and without the additional process of sample enrichment. Where reported, mean test turnaround times ranged from over 50% to 130% longer than manufacturer’s specification. Most studies had a low to unclear risk of bias.

Conclusions

Currently available Rapid Diagnostic Tests can potentially provide high diagnostic and detection capability for cholera. However, stronger evidence is required regarding the conditions required to secure these levels of accuracy in field use, particularly in low-resource settings.

Registration

PROSPERO (CRD42016048428).

Effectiveness of case-area targeted interventions including vaccination on the control of epidemic cholera: protocol for a prospective observational study

INTRODUCTION

Cholera outbreaks in fragile settings are prone to rapid expansion. Case-area targeted interventions (CATIs) have been proposed as a rapid and efficient response strategy to halt or substantially reduce the size of small outbreaks. CATI aims to deliver synergistic interventions (eg, water, sanitation, and hygiene interventions, vaccination, and antibiotic chemoprophylaxis) to households in a 100-250 m 'ring' around primary outbreak cases.

METHODS AND ANALYSIS

We report on a protocol for a prospective observational study of the effectiveness of CATI. Médecins Sans Frontières (MSF) plans to implement CATI in the Democratic Republic of the Congo (DRC), Cameroon, Niger and Zimbabwe. This study will run in parallel to each implementation. The primary outcome is the cumulative incidence of cholera in each CATI ring. CATI will be triggered immediately on notification of a case in a new area. As with most real-world interventions, there will be delays to response as the strategy is rolled out. We will compare the cumulative incidence among rings as a function of response delay, as a proxy for performance. Cross-sectional household surveys will measure population-based coverage. Cohort studies will measure effects on reducing incidence among household contacts and changes in antimicrobial resistance.

ETHICS AND DISSEMINATION

The ethics review boards of MSF and the London School of Hygiene and Tropical Medicine have approved a generic protocol. The DRC and Niger-specific versions have been approved by the respective national ethics review boards. Approvals are in process for Cameroon and Zimbabwe. The study findings will be disseminated to the networks of national cholera control actors and the Global Task Force for Cholera Control using meetings and policy briefs, to the scientific community using journal articles, and to communities via community meetings.

Inference is bliss: Simulation for power estimation for an observational study of a cholera outbreak intervention

Background

The evaluation of ring vaccination and other outbreak-containment interventions during severe and rapidly-evolving epidemics presents a challenge for the choice of a feasible study design, and subsequently, for the estimation of statistical power. To support a future evaluation of a case-area targeted intervention against cholera, we have proposed a prospective observational study design to estimate the association between the strength of implementation of this intervention across several small outbreaks (occurring within geographically delineated clusters around primary and secondary cases named ‘rings’) and its effectiveness (defined as a reduction in cholera incidence). We describe here a strategy combining mathematical modelling and simulation to estimate power for a prospective observational study.

Methodology and principal findings

The strategy combines stochastic modelling of transmission and the direct and indirect effects of the intervention in a set of rings, with a simulation of the study analysis on the model results. We found that targeting 80 to 100 rings was required to achieve power ≥80%, using a basic reproduction number of 2.0 and a dispersion coefficient of 1.0–1.5.

Conclusions

This power estimation strategy is feasible to implement for observational study designs which aim to evaluate outbreak containment for other pathogens in geographically or socially defined rings.

From Ebola virus disease outbreaks to the COVID-19 pandemic, the use of real-time evaluations of interventions to contain outbreaks is vital for rapidly estimating impact during the outbreak itself. Such evaluations must be both epidemiologically rigorous and logistically feasible to justify their conduct during an outbreak. In this short report, we report on the process (with R code) and the results of a simulation strategy that we devised for power estimation for a prospective observational study of a novel intervention (“case-area targeted intervention”) to contain cholera case clusters that present at the start of a new outbreak. We used simulation in two ways: mathematical modelling to simulate the impacts of a cholera outbreak and the intervention, and simulation of the study analysis on the model results. The strategy provided estimates of the sample sizes of study units required to achieve 80% and 90% power. Our findings reinforce that this process is feasible to implement for similar observational study designs which aim to evaluate outbreak containment for other pathogens in geographically or socially defined rings.

Contrasting Epidemiology of Cholera in Bangladesh and Africa

In Bangladesh and West Bengal cholera is seasonal, transmission occurs consistently annually. By contrast, in most African countries, cholera has inconsistent seasonal patterns and long periods without obvious transmission. Transmission patterns in Africa occur during intermittent outbreaks followed by elimination of that genetic lineage. Later another outbreak may occur because of reintroduction of new or evolved lineages from adjacent areas, often by human travelers. These then subsequently undergo subsequent elimination. The frequent elimination and reintroduction has several implications when planning for cholera's elimination including: a) reconsidering concepts of definition of elimination, b) stress on rapid detection and response to outbreaks, c) more effective use of oral cholera vaccine and WASH, d) need to readjust estimates of disease burden for Africa, e) re-examination of water as a reservoir for maintaining endemicity in Africa. This paper reviews major features of cholera's epidemiology in African countries which appear different from the Ganges Delta.

Cholera Rapid Diagnostic Tests for the Detection of Vibrio cholerae O1: An Updated Meta-Analysis

The rapid diagnosis of cholera contributes to adequate outbreak management. This meta-analysis assesses the diagnostic accuracy of cholera rapid tests (RDTs) to detect Vibrio cholerae O1. Methods: Systematic review and meta-analysis. We searched four databases (Medline, EMBASE, Google Scholar, and Web of Science up to 8 September 2021) for studies that evaluated cholera RDTs for the detection of V. cholerae O1 compared with either stool culture or polymerase chain reaction (PCR). We assessed the studies’ quality using the QUADAS-2 criteria. In addition, in this update, GRADE approach was used to rate the overall certainty of the evidence. We performed a bivariate random-effects meta-analysis to calculate the pooled sensitivity and specificity of cholera RDTs. Results: Overall, 20 studies were included in this meta-analysis. Studies were from Africa (n = 11), Asia (n = 7), and America (Haiti; n = 2). They evaluated eight RDTs (Crystal VC-O1, Crystal VC, Cholkit, Institut Pasteur cholera dipstick, SD Bioline, Artron, Cholera Smart O1, and Smart II Cholera O1). Using direct specimen testing, sensitivity and specificity of RDTs were 90% (95% CI, 86 to 93) and 86% (95% CI, 81 to 90), respectively. Cholera Sensitivity was higher in studies conducted in Africa [92% (95% CI, 89 to 94)] compared with Asia [82% (95% CI, 77 to 87)]. However, specificity [83% (95% CI, 71 to 91)] was lower in Africa compared with Asia [90% (95% CI, 84 to 94)]. GRADE quality of evidence was estimated as moderate. Conclusions: Against culture or PCR, current cholera RDTs have moderate sensitivity and specificity for detecting Vibrio cholerae O1.

Effectiveness of hygiene kit distribution to reduce cholera transmission in Kasaï-Oriental, Democratic Republic of Congo, 2018: a prospective cohort study

INTRODUCTION

Household contacts of cholera cases are at a greater risk of Vibrio cholerae infection than the general population. There is currently no agreed standard of care for household contacts, despite their high risk of infection, in cholera response strategies. In 2018, hygiene kit distribution and health promotion was recommended by Médecins Sans Frontières for admitted patients and accompanying household members on admission to a cholera treatment unit in the Democratic Republic of Congo.

METHODS

To investigate the effectiveness of the intervention and risk factors for cholera infection, we conducted a prospective cohort study and followed household contacts for 7 days after patient admission. Clinical surveillance among household contacts was based on self-reported symptoms of cholera and diarrhoea, and environmental surveillance through the collection and analysis of food and water samples.

RESULTS

From 94 eligible households, 469 household contacts were enrolled and 444 completed follow-up. Multivariate analysis suggested evidence of a dose-response relationship with increased kit use associated with decreased relative risk of suspected cholera: household contacts in the high kit-use group had a 66% lower incidence of suspected cholera (adjusted risk ratio (aRR) 0.34, 95% CI 0.11 to 1.03, p=0.055), the mid-use group had a 53% lower incidence (aRR 0.47, 95% CI 0.17 to 1.29, p=1.44) and low-use group had 22% lower incidence (aRR 0.78, 95% CI 0.24 to 2.53, p=0.684), compared with household contacts without a kit. Drinking water contamination was significantly reduced among households in receipt of a kit. There was no significant effect on self-reported diarrhoea or food contamination.

CONCLUSION

The integration of a hygiene kit intervention to case-households may be effective in reducing cholera transmission among household contacts and environmental contamination within the household. Further work is required to evaluate whether other proactive localised distribution among patients and case-households or to households surrounding cholera cases can be used in future cholera response programmes in emergency contexts.

Accuracy of cholera rapid diagnostic tests: a systematic review and meta-analysis

BACKGROUND

Cholera is an acute diarrheal disease caused by Vibrio cholerae O1 or O139. Cholera rapid diagnostic tests (RDTs) are widely used to screen for cholera cases. However, their accuracy has not been systematically reviewed.

OBJECTIVES

To evaluate the diagnostic accuracy of cholera RDTs.

METHODS

Systematic review and meta-analysis.

DATA SOURCES

Medline, EMBASE and Web of science through to November 2020; references of included studies and a technical guidance on cholera RDTs. This review is registered with PROSPERO (CRD42021233124).

STUDY ELIGIBILITY CRITERIA

Cross-sectional studies comparing the performance of cholera RDTs either to stool culture or PCR.

PARTICIPANTS

Individuals with clinically suspected cholera.

DATA EXTRACTION

Two authors independently extracted data and assessed the quality using Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) criteria.

RESULTS

Eighteen studies were included in the systematic review of which 17 were used for meta-analysis. Crystal VC was the most frequently used RDT (13 studies), followed by Cholkit and Institut Pasteur cholera dipstick (three studies each), SD Bioline (two studies), Artron (one study) and Smart (one study). Using direct testing (n = 12 627 specimens), the bivariate random-effects model yielded a pooled sensitivity and specificity of 91% (95% CI 87%-94%) and 80% (95% CI 74%-84%), respectively. However, through alkaline peptone water (APW) enrichment (n = 3403 specimens), the pooled sensitivity and specificity were 89% (95% CI 79%-95%) and 98% (95% CI 95%-99%), respectively.

CONCLUSION

Cholera RDTs, especially when enriched with APW, have moderate sensitivity and specificity. Although less useful for clinical management, the current generation of RDTs have clear utility for surveillance efforts if used in a principled manner. Enrichment of stool specimens in APW before using cholera RDTs reduces the possibility of obtaining false-positive results, despite the few cholera cases that go undetected. It is noteworthy that APW-enriched cholera RDTs are not necessarily rapid tests, and are not listed in the Global Task Force on Cholera Control/WHO target product profile.

Laboratory and Field Evaluation of the Crystal VC-O1 Cholera Rapid Diagnostic Test

Cholera is a severe acute, highly transmissible diarrheal disease which affects many low- and middle-income countries. Outbreaks of cholera are confirmed using microbiological culture, and additional cases during the outbreak are generally identified based on clinical case definitions, rather than laboratory confirmation. Many low-resource areas where cholera occurs lack the capacity to perform culture in an expeditious manner. A simple, reliable, and low-cost rapid diagnostic test (RDT) would improve identification of cases allowing rapid response to outbreaks. Several commercial RDTs are available for cholera testing with two lines to detect either serotypes O1 and O139; however, issues with sensitivity and specificity have not been optimal with these bivalent tests. Here, we report an evaluation of a new commercially available cholera dipstick test which detects only serotype O1. In both laboratory and field studies in Kenya, we demonstrate high sensitivity (97.5%), specificity (100%), and positive predictive value (100%) of this new RDT targeting only serogroup O1. This is the first field evaluation for the new Crystal VC-O1 RDT; however, with these high-performance metrics, this RDT could significantly improve cholera outbreak detection and improve surveillance for better understanding of cholera disease burden.

Successive epidemic waves of cholera in South Sudan between 2014 and 2017: a descriptive epidemiological study

BACKGROUND

Between 2014 and 2017, successive cholera epidemics occurred in South Sudan within the context of civil war, population displacement, flooding, and drought. We aim to describe the spatiotemporal and molecular features of the three distinct epidemic waves and explore the role of vaccination campaigns, precipitation, and population movement in shaping cholera spread in this complex setting.

METHODS

In this descriptive epidemiological study, we analysed cholera linelist data to describe the spatiotemporal progression of the epidemics. We placed whole-genome sequence data from pandemic Vibrio cholerae collected throughout these epidemics into the global phylogenetic context. Using whole-genome sequence data in combination with other molecular attributes, we characterise the relatedness of strains circulating in each wave and the region. We investigated the association of rainfall and the instantaneous basic reproduction number using distributed lag non-linear models, compared county-level attack rates between those with early and late reactive vaccination campaigns, and explored the consistency of the spatial patterns of displacement and suspected cholera case reports.

FINDINGS

The 2014 (6389 cases) and 2015 (1818 cases) cholera epidemics in South Sudan remained spatially limited whereas the 2016-17 epidemic (20 438 cases) spread among settlements along the Nile river. Initial cases of each epidemic were reported in or around Juba soon after the start of the rainy season, but we found no evidence that rainfall modulated transmission during each epidemic. All isolates analysed had similar genotypic and phenotypic characteristics, closely related to sequences from Uganda and Democratic Republic of the Congo. Large-scale population movements between counties of South Sudan with cholera outbreaks were consistent with the spatial distribution of cases. 21 of 26 vaccination campaigns occurred during or after the county-level epidemic peak. Counties vaccinated on or after the peak incidence week had 2·2 times (95% CI 2·1-2·3) higher attack rates than those where vaccination occurred before the peak.

INTERPRETATION

Pandemic V cholerae of the same clonal origin was isolated throughout the study period despite interepidemic periods of no reported cases. Although the complex emergency in South Sudan probably shaped some of the observed spatial and temporal patterns of cases, the full scope of transmission determinants remains unclear. Timely and well targeted use of vaccines can reduce the burden of cholera; however, rapid vaccine deployment in complex emergencies remains challenging.

FUNDING

The Bill & Melinda Gates Foundation.

Field Evaluation of Cholkit Rapid Diagnostic Test for Vibrio Cholerae O1 During a Cholera Outbreak in Malawi, 2018

Rapid diagnostic tests (RDTs) for cholera are an important emerging tool for surveillance, yet the currently available tests have several limitations. We assess the performance of a new RDT, Cholkit, during a cholera outbreak in Malawi compared with culture and find a sensitivity of 93.0% (95% CI, 83.0%–98.1%) and a specificity of 95.7% (95% CI, 78.1%–100.0%).

Gold Standard Cholera Diagnostics Are Tarnished by Lytic Bacteriophage and Antibiotics

A fundamental, clinical, and scientific concern is how lytic bacteriophage, as well as antibiotics, impact diagnostic positivity. Cholera was chosen as a model disease to investigate this important question, because cholera outbreaks enable large enrollment, field methods are well established, and the predatory relationship between lytic bacteriophage and the etiologic agent Vibrio cholerae share commonalities across bacterial taxa. Patients with diarrheal disease were enrolled at two remote hospitals in Bangladesh. Diagnostic performance was assessed as a function of lytic bacteriophage detection and exposure to the first-line antibiotic azithromycin, detected in stool samples by mass spectrometry. Among diarrheal samples positive by nanoliter quantitative PCR (qPCR) for V. cholerae (n = 78/849), the odds that a rapid diagnostic test (RDT) or qPCR was positive was reduced by 89% (odds ratio [OR], 0.108; 95% confidence interval [CI], 0.002 to 0.872) and 87% (OR, 0.130; 95% CI, 0.022 to 0.649), respectively, when lytic bacteriophage were detected. The odds that an RDT or qPCR was positive was reduced by more than 99% (OR, 0.00; 95% CI, 0.00 to 0.28) and 89% (OR, 0.11; 95% CI, 0.03 to 0.44), respectively, when azithromycin was detected. Analysis of additional samples from South Sudan found similar phage effects on RDTs; antibiotics were not assayed. Cholera burden estimates may improve by accommodating for the negative effects of lytic bacteriophage and antibiotic exposure on diagnostic positivity. One accommodation is using bacteriophage detection as a proxy for pathogen detection. These findings have relevance for other diagnostic settings where bacterial pathogens are vulnerable to lytic bacteriophage predation.

Diagnostic techniques for rapid detection of Vibrio cholerae O1/O139

Cholera caused by the toxigenic Vibrio cholerae is still a major public health problem in many countries. This disease is mainly due to poor sanitation, hygiene and consumption of unsafe water. Several recent epidemics of cholera showed its increasing intensity, duration and severity of the illness. This indicates an urgent need for effective management and preventive measures in controlling the outbreaks and epidemics. In preventing and spread of epidemic cholera, rapid diagnostic tests (RDTs) are useful in screening suspected stool specimens, water/food samples. Several RDTs developed recently are considered as investigative tools in confirming cholera cases, as the culture techniques are difficult to establish and/or maintain. The usefulness of RDTs will be more at the point-of-care facilities as it helps to make appropriate decisions in the management of outbreaks or epidemiological surveillance by the public health authorities. Apart from RDTs, several other tests are available for the direct detection of either V. cholerae or its cholera toxin. Viable but non-culturable (VBNC) state of V. cholerae poses a great challenge in developing RDTs. The aim of this article is to provide an overview of current knowledge about RDT and other techniques with reference to their status and future potentials in detecting cholera/V. cholerae.

Two cases of cholera O1 in South Batinah, Oman, April 2019: lessons learned

Cholera represents an ongoing threat to many low-income and middle-income countries, but some cases of cholera even occur in high-income countries. Therefore, to prevent or combat cholera outbreaks, it is necessary to maintain the capacity to rapidly detect cholera cases, implement infection control measures, and improve general hygiene in terms of the environment, water, and food. The 2 cases, 1 imported and 1 secondary, described herein are broadly indicative of areas that require improvement. These cases were missed at the primary health care stage, which should be the first detection point even for unusual diseases such as cholera, and the absence of strict infection control practices at the primary care level is believed to contribute to secondary cases of infection. This report also encourages countries to ensure that rapid diagnostic stool tests are available to enable quick detection, as well as to provide information to people travelling to areas where cholera is endemic.

Utilization of Small RNA Genes to Distinguish Vibrio cholerae Biotypes via Multiplex Polymerase Chain Reaction

The diarrheal disease "cholera" is caused by Vibrio cholerae, and is primarily confined to endemic regions, mostly in Africa and Asia. It is punctuated by outbreaks and creates severe challenges to public health. The disease-causing strains are most-often members of serogroups O1 and O139. PCR-based methods allow rapid diagnosis of these pathogens, including the identification of their biotypes. However, this necessitates the selection of specific target sequences to differentiate even the closely related biotypes of V. cholerae. Oligonucleotides for selective amplification of small RNA (sRNA) genes that are specific to these V. cholerae subtypes were designed. The resulting multiplex PCR assay was validated using V. cholerae cultures (i.e., 19 V. cholerae and 22 non-V. cholerae isolates) and spiked stool samples. The validation using V. cholerae cultures and spiked stool suspensions revealed detection limits of 10-100 pg DNA per reaction and 1.5 cells/mL suspension, respectively. The multiplex PCR assay that targets sRNA genes for amplification enables the sensitive and specific detection, as well as the differentiation of V. cholerae-O1 classical, O1 El Tor, and O139 biotypes. Most importantly, the assay enables fast and cheaper diagnosis compared with classic culture-based methods.

Integrated LAMP and immunoassay platform for diarrheal disease detection

The challenges of diagnosing infectious disease, especially in the developing world, and the shortcomings of available instrumentation have exposed the need for portable, easy-to-use diagnostic tools capable of detecting the wide range of causative microbes while operating in low resource settings. We present a centrifugal microfluidic platform that combines ultrasensitive immunoassay and isothermal amplification-based screening for the orthogonal detection of both protein and nucleic acid targets at the point-of-care. A disposable disc with automatic aliquoting inlets is paired with a non-contact heating system and precise rotary control system to yield an easy-to-use, field-deployable platform with versatile screening capabilities. The detection of three enterotoxins (cholera toxin, Staphylococcal enterotoxin B, and Shiga-like toxin 1) and three enteric bacteria (C. jejuni, E. coli, and S. typhimurium) were performed independently and shown to be highly sensitive (limit of detection = 1.35-5.50 ng/mL for immunoassays and 1-30 cells for isothermal amplification), highly exclusive in the presence of non-specific targets, and capable of handling a complex sample matrix like stool. The full panel of toxins and bacteria were reliably detected simultaneously on a single disc at clinically relevant sample concentrations in less than an hour. The ability of our technology to detect multiple analyte types in parallel at the point-of-care can serve a variety of needs, from routine patient care to outbreak triage, in a variety of settings to reduce disease impact and expedite effective treatment.

Confirmation of cholera by rapid diagnostic test amongst patients admitted to the cholera treatment centre in Uvira, Democratic Republic of the Congo

INTRODUCTION

Cholera is endemic in the Eastern provinces of the Democratic Republic of the Congo since 1978, and Uvira in South-Kivu has been reporting suspected cholera cases nearly every week for over a decade. The clinical case definition for suspected cholera is relatively non-specific, and cases are rarely confirmed by laboratory methods, especially in endemic settings. This may lead to over-estimation of cholera cases and limit effective public health responses.

METHODS AND RESULTS

Between April 2016 and November 2017, 69% of the 2,059 patients admitted to the Uvira Cholera Treatment Centre (CTC) were tested for cholera with rapid diagnostic tests (RDTs). Of those admitted as suspected cholera cases, only 40% tested positive for cholera, equivalent to an estimated annual incidence of suspected/confirmed cholera in Uvira of 43.8 and 16.3 cases per 10,000 inhabitants respectively. A multivariable logistic regression indicates that boys aged 2 to 4 years, girls aged 5 to 15 years and adult men are respectively 1.9, 2.1 and 1.8 times more likely to test positive than adult women. On the contrary, boys under 2 are 10 times less likely to test positive. The odds of testing positive also increase as weekly admissions to the CTC rise, with up to a 5-fold increase observed during the weeks with the highest numbers of admissions compared to the lowest ones. Other predictors of cholera confirmation include duration of stay at the CTC, clinical outcome of admission, lower weekly rainfall and area of residence in Uvira, with the northern part of town having the highest confirmation rate.

CONCLUSION

Cholera is an on-going public health problem in Uvira but the majority of suspected cases admitted to the CTC were found to be negative for cholera after RDT testing. These findings may have important implications for cholera control strategies in favour of interventions that address cholera and other diarrhoeal diseases alike.

Evaluation of the SD bioline cholera rapid diagnostic test during the 2016 cholera outbreak in Lusaka, Zambia

OBJECTIVE

To assess the performance of the SD Bioline Cholera Ag O1/O139 rapid diagnostic test (RDT) compared to a reference standard combining culture and PCR for the diagnosis of cholera cases during an outbreak.

METHODS

RDT and bacterial culture were performed on site using fresh stools collected from cholera suspected cases, and from stools enriched in alkaline peptone water. Dried stool samples on filter paper were tested for V. cholerae by PCR in Lusaka (as part of a laboratory technology transfer project) and at a reference laboratory in Paris, France. A sample was considered positive for cholera by the reference standard if any of the culture or PCR tests was positive for V. cholerae O1 or O139.

RESULTS

Among the 170 samples tested with SD Bioline and compared to the reference standard, the RDT showed a sensitivity of 90.9% (95% CI: 81.3-96.6) and specificity of 95.2% (95% CI: 89.1-98.4). After enrichment, the sensitivity was 95.5% (95% CI: 87.3-99.1) and specificity 100% (95% CI: 96.5-100).

CONCLUSION

The observed sensitivity and specificity were within recommendations set by the Global Task Force for Cholera Control on the use of cholera RDT (sensitivity = 90%; specificity = 85%). Although the sample size was small, our findings suggest that the SD Bioline RDT could be used in the field to rapidly alert public health officials to the likely presence of cholera cases when an outbreak is suspected.

Cholera: under diagnosis and differentiation from other diarrhoeal diseases

BACKGROUND

Globally 1.4 billion people are at risk from cholera in countries where the disease is endemic, with an estimated 2.8 million cases annually. The disease is significantly under reported due to economic, social and political disincentives as well as poor laboratory resources and epidemiological surveillance in those regions. In addition, identification of cholera from other diarrhoeal causes is often difficult due to shared pathology and symptoms with few reported cases in travellers from Northern Europe.

METHODS

A search of PubMed and Ovid Medline for publications on cholera diagnosis from 2010 through 2017 was conducted. Search terms included were cholera, Rapid Diagnostic Test (RDT), multiplex PCR and diagnosis of diarrhoea. Studies were included if they are published in English, French or Spanish.

RESULTS

An increase of RDT study publications for diarrhoeal disease and attempted test validations were seen over the publication period. RDTs were noted as having varied selectivity and specificity, as well as associated costs and local resource requirements that can prohibit their use.

CONCLUSIONS

Despite opportunities to employ RDTs with high selectivity and specificity in epidemic areas, or in remote locations without access to health services, such tests are limited to surveillance use. This may represent a missed opportunity to discover the true global presence of Vibrio cholerae and its role in all cause diarrhoeal disease in underdeveloped countries and in travellers to those areas. The wider applicability of RDTs may also represent an opportunity in the wider management of traveller's diarrhoea.

Changing facades of Vibrio cholerae: An enigma in the epidemiology of cholera

Cholera, caused by the Gram-negative bacterium Vibrio cholerae, has ravaged humanity from time immemorial. Although the disease can be treated using antibiotics along with administration of oral rehydration salts and controlled by good sanitation, cholera is known to have produced mayhems in ancient times when little was known about the pathogen. By the 21st century, ample information about the pathogen, its epidemiology, genetics, treatment and control strategies was revealed. However, there is still fear of cholera outbreaks in developing countries, especially in the wake of natural calamities. Studies have proved that the bacterium is mutating and evolving, out-competing all our efforts to treat the disease with previously used antibiotics and control with existing vaccines. In this review, the major scientific insights of cholera research are discussed. Considering the important role of biofilm formation in the V. cholerae life cycle, the vast availability of next-generation sequencing data of the pathogen and multi-omic approach, the review thrusts on the identification of suitable biofilm-inhibiting targets and the discovery of anti-biofilm drugs from nature to control the disease.

Laboratory evaluation of immunochromatographic rapid diagnostic tests for cholera in Haiti

Background

Rapid diagnostic tests (RDT) for cholera are promising tools for detecting cholera in areas with limited laboratory infrastructure. However, evidence on the characteristics of the many available RDTs is scarce, and their use has been limited by suboptimal performance. We evaluated the performance characteristics of three cholera RDTs from Span Diagnostics, Artron Laboratories, and Standard Diagnostics in a regional laboratory in Haiti.

Methodology/Principal findings

We retrospectively reviewed records from May 2014 to October 2015 of a laboratory-based surveillance program for Vibrio cholerae at Hôpital Saint-Nicolas in Saint-Marc, Haiti. We compared the results of 511 Crystal VC, 129 Artron and 451 SD Bioline RDTs to bacterial culture as the gold standard. Of 905 cultures, 477 (52.7%) were positive for V. cholerae O1, of which 27.7% were serotype Inaba. No cultures grew V. cholerae O139. Sensitivity and specificity of Crystal VC were 98.6% (95%CI: 96.5%-99.6%) and 71.1% (95%CI: 64.7%-76.9%), respectively. Artron demonstrated a sensitivity of 98.6% (95%CI: 92.7%-100%) and specificity of 69.1% (95%CI: 55.2%-80.9%). SD Bioline demonstrated a sensitivity of 81.1% (95%CI: 75.6%-85.8%) and specificity of 92.8% (95%CI: 88.4%-95.9%). Crystal VC and Artron frequently showed false positive O139 bands, whereas none were seen with SD Bioline.

Conclusions/Significance

There is significant variation in the performance of different cholera diagnostic RDTs. Artron and Crystal VC RDTs have high sensitivity and low specificity, while SD Bioline RDT has low to moderate sensitivity and high specificity when performed by laboratory technicians in Haiti. Study limitations included its retrospective design. The suboptimal characteristics of these tests limit their use as clinical point-of-care tests; however, they may be useful in outbreak response, surveillance, and research in resource-limited settings.

Neighborhood-targeted and case-triggered use of a single dose of oral cholera vaccine in an urban setting: Feasibility and vaccine coverage

INTRODUCTION

In June 2015, a cholera outbreak was declared in Juba, South Sudan. In addition to standard outbreak control measures, oral cholera vaccine (OCV) was proposed. As sufficient doses to cover the at-risk population were unavailable, a campaign using half the standard dosing regimen (one-dose) targeted high-risk neighborhoods and groups including neighbors of suspected cases. Here we report the operational details of this first public health use of a single-dose regimen of OCV and illustrate the feasibility of conducting highly targeted vaccination campaigns in an urban area.

METHODOLOGY/PRINCIPAL FINDINGS

Neighborhoods of the city were prioritized for vaccination based on cumulative attack rates, active transmission and local knowledge of known cholera risk factors. OCV was offered to all persons older than 12 months at 20 fixed sites and to select groups, including neighbors of cholera cases after the main campaign ('case-triggered' interventions), through mobile teams. Vaccination coverage was estimated by multi-stage surveys using spatial sampling techniques. 162,377 individuals received a single-dose of OCV in the targeted neighborhoods. In these neighborhoods vaccine coverage was 68.8% (95% Confidence Interval (CI), 64.0-73.7) and was highest among children ages 5-14 years (90.0%, 95% CI 85.7-94.3), with adult men being less likely to be vaccinated than adult women (Relative Risk 0.81, 95% CI: 0.68-0.96). In the case-triggered interventions, each lasting 1-2 days, coverage varied (range: 30-87%) with an average of 51.0% (95% CI 41.7-60.3).

CONCLUSIONS/SIGNIFICANCE

Vaccine supply constraints and the complex realities where cholera outbreaks occur may warrant the use of flexible alternative vaccination strategies, including highly-targeted vaccination campaigns and single-dose regimens. We showed that such campaigns are feasible. Additional work is needed to understand how and when to use different strategies to best protect populations against epidemic cholera.