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.
Critical failings in humanitarian response: a cholera outbreak in Kumer Refugee Camp, Ethiopia, 2023
BACKGROUND
In 2019–2020, preventative Oral Cholera Vaccine campaigns were conducted in 24/32 non-contiguous health areas of Goma, DR Congo. In August 2022, we measured coverage and factors potentially influencing success of the delivery strategy.
METHODS
We used random geo-sampled stratified cluster survey to estimate OCV coverage and assess population movement, diarrhea history, and reasons for non-vaccination.
RESULTS
603 households were visited. Coverage with at least one dose was 46.4 % (95 %CI: 41.8–51.0), and 50.1 % (95 %CI: 45.4–54.8) in areas targeted by vaccination compared to 26.3 % (95 %CI: 19.2–34.9) in non-targeted areas. Additionally, 7.0 % of participants reported moving from outside Goma since 2019, and 5.4 % reported history of severe diarrhea. Absence and unawareness were the main reasons for non-vaccination.
CONCLUSION
Results suggest that targeting non-contiguous urban areas had a coverage-diluting effect. Targeting entire geographically contiguous areas, adapted distribution, and regular catch-up campaigns are operational recommendations to reach higher coverages arising from the study.
We evaluated the spatiotemporal clustering of rapid diagnostic test−positive cholera cases in Uvira, eastern Democratic Republic of the Congo. We detected spatiotemporal clusters that consistently overlapped with major rivers, and we outlined the extent of zones of increased risk that are compatible with the radii currently used for targeted interventions.
The risk of cholera outbreaks spreading rapidly and extensively is substantial. Case-area targeted interventions (CATI) are based on the premise that early detection can trigger a rapid, localised response in the high-risk radius around case-households to reduce transmission sufficiently to extinguish the outbreak or reduce its spread, as opposed to relying on resource-intensive mass interventions. Current evidence supports intervention in a high-risk spatiotemporal zone of up to 200 m around case- households for 5 days after case presentation. Médecins Sans Frontières (MSF) started delivering CATI to people living within these high-risk rings during outbreaks in the Democratic Republic of the Congo in April 2022. We present the results of a prospective observational study designed to evaluate the CATI strategy, measuring effectiveness, feasibility, timeliness, and resource requirements, and we extract operational learnings.
METHODS
Between April 2022 and April 2023, MSF delivered the holistic CATI package in five cholera-affected regions. The package incorporated key interventions combining household-level water, sanitation, and hygiene measures, health promotion, antibiotic chemoprophylaxis, and single-dose oral cholera vaccination (OCV). We conducted a survey in each ring roughly 3 weeks after the intervention to estimate coverage and uptake of the different components. We measured effectiveness by comparing cholera incidence in the first 30 days between rings with different delays from primary case presentation to CATI implementation, using a Bayesian regression model and adjusting for covariates such as population density, age, and access to water and sanitation.
RESULTS
During the study, four MSF operational sections implemented 118 CATI rings in five sites. The median number of households per ring was 70, the median OCV coverage was 85%, and the median time from presentation of the primary case to CATI implementation and to vaccination was 2 days and 3 days, respectively. These characteristics varied widely across sites and between rings. No secondary cases were observed in 81 (78%) of 104 rings included in the analysis, and we noted a (non- significant) decreasing trend in the number of secondary cases with decreasing delay to CATI implementation, e.g. 1.3 cases [95% CrI 0.01–4.9] for CATI implementation starting within 5 days from primary case presentation, and 0.5 cases [0.03–2.0] for CATI starting within 2 days.
CONCLUSION
Our results show that rapid implementation of CATI with vaccination is feasible in complex contexts. The number of secondary cases was low when CATI was implemented promptly. This highly targeted approach may be an effective strategy to quickly protect people most at risk and is resource- efficient if implemented early to extinguish localised outbreaks before they require mass interventions.
