Cholera outbreak in a southwest community of Nigeria: investigation of risk factors and evaluation of a district surveillance system

Following confirmation of cholera outbreak in a southwest community of Nigeria, we set to identify possible risk factors for contracting the disease and to evaluate the completeness as well as the representativeness of the cases reported to a district health authority. Cholera cases were identified through an active case search that involved the review of records in health facilities and a house-to-house search using the standard case definition in the Nigeria integrated disease surveillance and response technical guidelines. Two neighborhood controls appropriately matched on age and sex for each case, were also identified. An interviewer-administered questionnaire was used to collect information on the demographic characteristics and potential risk factors. Completeness of reporting of cases notified to the district health authority was evaluated using a two source capture-recapture method. In addition, the representativeness of the reported cases was determined by comparing the age and sex distributions of notified cases to those identified through the active case search. Thirty-nine cases were identified, of which 22 consented to participate. Contact with a diarrhoea case at home or in the neighborhood within the last 7 days prior to illness onset in cases was significantly associated with having cholera (Matched triplets Odds Ratio 8.5, 95% CI: 1.36-52.9). The completeness of the district surveillance report was estimated to be 54%. In the district notification data compared with the active case search data, males