Case-area targeted intervention (CATI) for cholera outbreaks: a prospective observational study

Background

Globally, the risk of small-scale cholera outbreaks propagating rapidly and enlarging extensively remains substantial. As opposed to relying on mass, community-wide approaches, cholera control strategies could focus on proactively containing the first clusters. Case-area targeted interventions (CATI) are based on the premise that early cluster detection can trigger a rapid, localised response in the high-risk radius around one or several households to reduce transmission sufficiently to extinguish the outbreak or reduce its spread. Current evidence supports a high-risk spatiotemporal zone of 100 to 250 meters around case-households for 7 days.

We hypothesize that the prompt application of CATI will reduce household transmission and transmission in the wider ring. This will result in reduced incidence in the ring and reduced clustering of cases. The local focus of CATI will enable active case-finding and sustained uptake of interventions. This will result in prompt access to care for detected cases, and reduced mortality and community transmission.

Methods

We propose to evaluate the effectiveness of a CATI strategy using an observational study design during an acute cholera epidemic, with clearly-defined measures of the effectiveness of the CATI package. In addition, we intend to evaluate the feasibility, costs, and process of implementing this approach. The CATI package delivered by Médecins Sans Frontières’ (MSF) will incorporate key transmission-reducing interventions (including household-level water, sanitation, and hygiene measures, active case-finding, antibiotic chemoprophylaxis, and, single-dose oral cholera vaccination (OCV)) which aim to rapidly reduce the risk of infection in the household and in the ring around the primary case household. MSF will decide on the contents of the CATI package used, the radius of intervention and the prioritization strategy used if the caseload is higher than the operational capacity, based on national policies, the local context, and operational considerations. In scenarios where preventative vaccination has been recently conducted or is planned, CATI and its evaluation will focus on implementation before and during the mass campaign, or in areas where vaccination coverage was sub-optimal.

The study design is based on comparing the effects of CATIs that rapidly provide protection in averting later generations of cases when compared with progressively-delayed CATIs. A regression analysis will be used to model the observed incidence of enriched RDT-positive cholera as a function of the delay to intervention (in days). The delay will reflect the inverse strength of rapid response. Groups, as a function of their delays to intervention, will serve as internal controls.

Case-area targeted interventions (CATI) are based on the premise that early cluster detection can trigger a rapid, localised response in the high-risk radius around one or several households to reduce transmission sufficiently to extinguish the outbreak or reduce its spread.

We propose to evaluate the effectiveness of a CATI strategy using an observational study design during an acute cholera epidemic, with clearly-defined measures of the effectiveness of the CATI package. In addition, we intend to evaluate the feasibility, costs, and process of implementing this approach. The CATI package delivered by Médecins Sans Frontières’ (MSF) will incorporate key transmission-reducing interventions (including household-level water, sanitation, and hygiene measures, active case-finding, antibiotic chemoprophylaxis, and, single-dose oral cholera vaccination (OCV) ) which aim to rapidly reduce the risk of infection in the household and in the ring around the primary case household.

CATI has been highlighted as a major component of the GTFCC’s global research agenda. Therefore, conducting a rigorous prospective evaluation of the effectiveness of CATI, which includes OCV and explains the pathway to impact, is an important and timely question for outbreak control.