Case-area targeted interventions to control cholera: a scoping review

Cholera is an acute diarrheal disease caused by ingesting water or food contaminated with Vibrio cholerae O1 or O139 (1). Once an individual contracts cholera, subsequent disease transmission is driven by poor hygiene practices as well as inadequate access to water, sanitation facilities, and health services (1,2). Neighbors in close proximity to cholera cases are often at an especially high risk of contracting the disease.

To control cholera outbreaks, mass campaigns have commonly been used, in which multi-sector interventions cover large areas thought to be at risk for infection. In 2017, the Global Task Force on Cholera Control proposed a targeted strategy that emphasizes the use of rapid response teams that conduct case-area targeted interventions (CATIs) (3). Rapid response measures targeting cholera case households and at-risk neighboring households can reduce or even stop disease transmission, especially when case clusters are detected early.

A recent scoping review by Ratnayake et al. has investigated the effectiveness of interventions to rapidly limit transmission, the optimal timeframe and spatial zone of intervention, and intervention feasibility (4). The study assessed reports of CATIs carried out in Douala (Cameroon), Haiti, Dhaka (Bangladesh), Juba (South Sudan), Kathmandu Valley (Nepal), Yemen and Kinshasa (Democratic Republic of the Congo).

To effectively reduce disease spread, interventions must rapidly address the major routes of transmission. The authors found that point-of-use water treatment (e.g., using chlorine tablets), hygiene promotion and antibiotic chemoprophylaxis can rapidly reduce household transmission. Rapidly acting interventions such household-level water, sanitation and hygiene (WASH) interventions are critical. Treatment of drinking water and improvement of handwashing and hygienic behaviors directly address the root causes of transmission. Antibiotic chemoprophylaxis can also protect uninfected and infected individuals and was shown to increase the effect of targeted WASH interventions. Furthermore, single-dose vaccination extended the duration of protection within the zone of intervention (4). 

An effective response also depends on determining the appropriate timeframe and radius for the zone of intervention. Four studies indicated a high-risk ring of 50–100 meters over seven days in urban and rural contexts, which was likely associated with intense household transmission and shared risk factors among households (4).

Although CATIs show promise for cholera outbreak control, effective interventions are critically dependent on surveillance capacity to rapidly detect cases.