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

Abstract

IntroductionCholera 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 analysisWe 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 disseminationThe 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.

Spatiotemporal Modeling of Cholera, Uvira, Democratic Republic of the Congo, 2016−2020

“…We detected spatiotemporal clustering of cholera outbreaks during 2016–2020 in Uvira, DRC, that could inform early mitigation of seasonal outbreaks. The clustering methods produced aligned results compatible with a high-risk radius of ≤500 meters, as previously used for CATI in DRC ( 7 , 13 ) and similar to clustering in Matlab, Bangladesh, and coastal Sabah, Malaysia (500 meters, ≈5 days after cases began) ( 3 , 14 ). For RDT-positive cases within 5 days after cases began, we estimated a 1,105-meter high-risk radius, showing that a ≤1,000-meter risk window is optimal.…”

Spatiotemporal modelling of cholera and implications for its control, Uvira, Democratic Republic of the Congo

“…Daily prospective scanning for local clustering could aid in early cluster detection across Uvira. (38) The radii of 100-500m used for a CATI strategies in DRC (17,43) are justified by these findings and could perhaps be enlarged further. A 600-1105m radius of infection risk would include several thousand persons and would be logistically prohibitive to cover rapidly (i.e., within the 3 to 5 day risk window).…”

“…which may seed larger outbreaks (18), and (c) sporadic cases after mass vaccination (15). Building on previous and current studies (9,10) and operational experience (17,43), a 200-600m radius can be used to narrow down areas for CATIs where transmission is likely.…”

A Quantitative and Qualitative Program Evaluation of a Case-Area Targeted Intervention to Reduce Cholera in Eastern Democratic Republic of the Congo

“…Furthermore, for those who were vaccinated, there was a surprise that the vaccine had not provided complete protection against cholera for themselves and those in their household and community. Numerous studies have described the potential benefits of cholera vaccine delivery inclusion in CATIs [12,17,21,50], though studies of real-world applications are limited and ongoing, often hampered by limited vaccine availability due to the low cholera vaccine stockpile globally [20,21,31,51,52]. In addition, with limitations in access to OCV supplies, challenges with OCV include the need for multiple doses, incomplete protection provided by vaccination, and low community awareness [53].…”