To evaluate the effectiveness of the CATI approach among household contacts in the reduction of cumulative incidence of cholera and explore the genome analysis and immune response of V. cholerae antigen from different hotspots in Dhaka city, cholera cases will be enrolled by rapid diagnostic test (RDT) from the diarrhoeal patients coming to icddr,b Dhaka hospital. Hotspots will be defined as the households (HHs) surrounding the RDT-positive cholera case (around 20-40m radius). The 'Case area targeted interventions' (CATI) will be given by administrating Oral Cholera Vaccine (OCV) with either one dose or two doses of OCV 1 month apart among household contacts (≥1-year age and non-pregnant women) and contacts of the contacts residing in the adjacent HHs. The passive surveillance for cholera will be followed using the icddr,b hospital, and other health facilities. Data on each individual's states of the clusters (e.g., susceptible, exposed, infectious, or recovered) will be tracked throughout the 3 years study follow-up.