Case-area targeted interventions and free chlorine residual in household drinking water: An observational cohort study during a cholera outbreak in Northeast Nigeria

Background Cholera outbreaks are surging worldwide. Growing research supports case-area targeted interventions (CATIs), whereby teams provide a package of interventions to case and neigh-boring households, as an effective strategy in cholera outbreak control, particularly in humanitarian settings. While research exists on individual CATI interventions, research gaps exist on outcomes of integrated interventions during CATI responses. Methodology/Principal findings We conducted a prospective observational cohort study on CATIs during the 2021 cholera outbreak in Northeast Nigeria. During CATI response in Borno, Adamawa, and Yobe, research enumerators accompanied CATI teams to households and observed interventions (including provision of soap, Aquatabs, educational materials, and jerrycans; latrine and bedding disinfection; and hygiene promotion) and collected data on demographics, existing household water, sanitation, and hygiene, and household water free chlorine residual (FCR). Enumerators returned to households 10–14 days later to conduct follow-up surveys. We tested differences in reported delivery and receipt of interventions, and household drinking water FCR concentrations before and after CATIs. We also analyzed the associated relationship between CATI and environmental factors and odds of FCR <0.2 mg/L using quasi-Poisson multivariate logistic regression models with generalized estimating equations (GEE). We found household drinking water FCR significantly increased (p<0.001) post-CATI in Adamawa state. Self-reported receipt of Aquatabs and handwashing station availability were significantly associated with reduced odds of FCR <0.2 mg/L at follow-up. Self-reported receipt of hygiene promotion lacked significant associations with FCR in both Ada-mawa and Borno. These associations varied by type of water source. Conclusions/Significance These findings suggest that CATIs improved household drinking water FCR, a key protec-tive measure against cholera, in Northeast Nigeria. Our research highlights factors associated with FCR concentrations <0.2 mg/L post-CATI in Adamawa and Borno, offering valuable insights for response planning, and overall supports the continued use of CATIs in humanitarian settings.