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.

Background (brief):

1. Burden: Annually, 2.8 million cases and 95,000 deaths due to cholera are estimated to occur in cholera-endemic countries of Asia, Latin and Central America, and sub-Saharan Africa. The risk of cholera infection within the household and also around the households of cholera cases is higher than in the overall population. Outbreaks of cholera are unpredictable and can occur both in endemic settings and nonendemic areas depending on environmental conditions, climate change, or any humanitarian crisis where sanitary infrastructure is being disrupted. New phenotypes and genotypes of V. cholerae strains are constantly evolving with outbreaks, resulting in an increased risk of antimicrobial resistance (AMR).
2. Knowledge gap: Standard cholera outbreak response and traditional vaccination campaign is time consuming, costly and usually delayed. A rapid response comprising an early detection of cholera case, hotspot identification and delivery of a rapid response to households around the case could reduce the transmission of disease. But it is not established that whether this early detection of cases and rapid intervention will reduce cholera transmission, also what number of oral cholera vaccine (OCV) will effectively reduce the transmission.
3. Relevance: Availability of OCV is scarce but necessary for rapid response as it an effective short-term single intervention to shortened the epidemic period and cholera cases. This study aims to evaluate the effectiveness of the CATI approach (single/two doses at 1-month intervals) among household contacts and their neighbours in the reduction of the incidence of cholera

Hypothesis: Case area targeted intervention with OCV reduce the incidence of cholera after defining cholera hotspot.

Objectives: This study aims to evaluate the effectiveness of the CATI approach (OCV- one dose, two doses at one-month interval) 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.

Methods: The investigators will enroll cholera cases (index) by rapid diagnostic test (RDT) from the diarrhoeal patients coming to icddr,b Dhaka Hospital in and around Dhaka city based on our inclusion and exclusion criteria. Hotspots will be defined as the households (HHs) surrounding the RDT-positive cholera case (around 20-40m radius). The CATIs will be given by administrating 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 investigators will enrol on average 150 participants in each cluster of the index cases on the same day of the enrolment within the nearest geographic boundary (around 20-40m radius). Passive surveillance for cholera will be followed using the icddr,b hospital, and other selected 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.

Index case eligibility

Inclusion Criteria:

1. Some to severe dehydrated diarrheal patient
2. Provide signed informed consent form

Exclusion criteria:

1. Resident in a ward already covered by OCV since 2015

Vaccination Eligibility

Inclusion Criteria:

1. Aged ≥1 year and non-pregnant
2. Meeting the definition of IHC and NHC
3. Provide signed informed consent form

Exclusion criteria:

1. History of taking OCV
2. Currently suffering from diarrhea
3. < 1 year of age
4. Pregnant women (verbally confirmed)
5. Index case