Cholera remains a public health threat but is inequitably distributed across sub-Saharan Africa. Lack of standardized reporting and inconsistent outbreak definitions limit our understanding of cholera outbreak epidemiology.
METHODS
From a database of cholera incidence and mortality, we extracted data from sub-Saharan Africa and reconstructed outbreaks of suspected cholera starting in January 2010 to December 2019 based on location-specific average weekly incidence rate thresholds. We then described the distribution of key outbreak metrics.
RESULTS
We identified 999 suspected cholera outbreaks in 744 regions across 25 sub-Saharan African countries. The outbreak periods accounted for 1.8 billion person-months (2% of the total during this period) from January 2010 to January 2020. Among 692 outbreaks reported from second-level administrative units (e.g., districts), the median attack rate was 0.8 per 1000 people (interquartile range (IQR), 0.3-2.4 per 1000), the median epidemic duration was 13 weeks (IQR, 8-19), and the median early outbreak reproductive number was 1.8 (range, 1.1-3.5). Larger attack rates were associated with longer times to outbreak peak, longer epidemic durations, and lower case fatality risks.
CONCLUSIONS
This study provides a baseline from which the progress toward cholera control and essential statistics to inform outbreak management in sub-Saharan Africa can be monitored.
Cholera remains a public health threat, but is inequitably distributed across sub-Saharan Africa. Lack of standardized reporting and inconsistent outbreak definitions limit our understanding of cholera outbreak epidemiology.
METHODS
From a database of cholera incidence and mortality, we extracted data from sub-Saharan Africa and reconstructed outbreaks of suspected cholera starting in January 2010 to December 2019 based on location-specific average weekly incidence rate thresholds. We then described the distribution of key outbreak metrics.
RESULTS
We identified 999 suspected cholera outbreaks in 744 regions across 25 sub-Saharan Africa countries, and outbreak periods accounted for 1.8 billion person-months (2% of the total during this period) from January 2010 through January 2020. Among 692 outbreaks reported from second-level administrative units (e.g., districts), the median attack rate was 0.8 per 1,000 people (IQR, 0.3-2.4 per 1,000), the median epidemic duration was 13 weeks (IQR, 8-19), and the median early outbreak reproductive number was 1.8 (range, 1.1-3.5). Larger attack rates were associated with longer times to outbreak peak, longer epidemic durations, and lower case fatality risks.
CONCLUSIONS
This work provides a baseline from which to monitor progress towards cholera control and essential statistics to inform outbreak management in sub-Saharan Africa.
Cholera is a bacterial water-borne diarrheal disease transmitted via the fecal-oral route that causes high morbidity in sub-Saharan Africa and Asia. It is preventable with vaccination, and Water, Sanitation, and Hygiene (WASH) improvements. However, the impact of vaccination in endemic settings remains unclear. Cholera is endemic in the city of Kalemie, on the shore of Lake Tanganyika, in the Democratic Republic of Congo, where both seasonal mobility and the lake, a potential environmental reservoir, may promote transmission. Kalemie received a vaccination campaign and WASH improvements in 2013-2016. We assessed the impact of this intervention to inform future control strategies in endemic settings.
We fit compartmental models considering seasonal mobility and environmentally-based transmission. We estimated the number of cases the intervention avoided, and the relative contributions of the elements promoting local cholera transmission.
We estimated the intervention avoided 5,259 cases (95% credible interval: 1,576.6-11,337.8) over 118 weeks. Transmission did not rely on seasonal mobility and was primarily environmentally-driven. Removing environmental exposure or contamination could control local transmission.
Repeated environmental exposure could maintain high population immunity and decrease the impact of vaccination in similar endemic areas. Addressing environmental exposure and contamination should be the primary target of interventions in such settings.
Cholera epidemics occur frequently in low-income countries affected by concurrent humanitarian crises. Evaluations of these epidemic response remains largely unpublished and there is a need to generate evidence on response efforts to inform future programmes. This review of MSF cholera epidemic responses aimed to describe the main characteristics of the cholera epidemics and related responses in these three countries, to identify challenges to different intervention strategies based on available data; and to make recommendations for epidemic prevention and control practice and policy.
METHODS
Case studies from the Democratic Republic of Congo, Malawi and Mozambique were purposively selected by MSF for this review due to the documented burden of cholera in each country, frequency of cholera outbreaks, and risk of humanitarian crises. Data were extracted on the characteristics of the epidemics; time between alert and response; and, the delivery of health and water, sanitation and hygiene interventions. A Theory of Change for cholera response programmes was built to assess factors that affected implementation of the responses.
RESULTS AND CONCLUSIONS
20 epidemic response reports were identified, 15 in DRC, one in Malawi and four in Mozambique. All contexts experienced concurrent humanitarian crises, either armed conflict or natural disasters. Across the settings, median time between the date of alert and date of the start of the response by MSF was 23 days (IQR 14-41). Almost all responses targeted interventions community-wide, and all responses implemented in-patient treatment of suspected cholera cases in either established health care facilities (HCFs) or temporary cholera treatment units (CTUs). In three responses, interventions were delivered as case-area targeted interventions (CATI) and four responses targeted households of admitted suspected cholera cases. CATI or delivery of interventions to households of admitted suspected cases occurred from 2017 onwards only. Overall, 74 factors affecting implementation were identified including delayed supplies of materials, insufficient quantities of materials and limited or lack of coordination with local government or other agencies. Based on this review, the following recommendations are made to improve cholera prevention and control efforts: explore improved models for epidemic preparedness, including rapid mobilisation of supplies and deployment of trained staff; invest in and strengthen partnerships with national and local government and other agencies; and to standardise reporting templates that allow for rigorous and structured evaluations within and across countries to provide consistent and accessible data.
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.
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
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.