Risk factors for cholera in Pohnpei during an outbreak in 2000: lessons for Pacific countries and territories

Abstract

In April 2000, a large outbreak of cholera due to Vibrio cholerae serotype Ogawa biotype El Tor affected the Island of Pohnpei in the Federated States of Micronesia. A Pacific Public Health Surveillance Network team conducted a case control study in the middle of the epidemic. The aims of the study were to identify individual and household level risk factors for cholera, and to evaluate public health interventions aimed at controlling the outbreak. A case was a person admitted to the Pohnpei hospital with acute watery diarrhoea in the months of June and July 2000. We used a pre-tested questionnaire to interview cases about exposures in the five days prior to illness and visited their house to collect water samples, observe hygiene, and assess uptake of health education. 100 mL water samples were filtered and cultured for V. cholerae. We randomly selected neighbouring houses to identify a control that was similar age and sex for each case. Identical observations were made for eligible controls where their household members had not had diarrhoea since the beginning of the epidemic. We stored and analysed data using an Epi Info version 6.04. 53 case control pairs were enrolled into the study. The study identified that storing food outside uncovered, and having a pit latrine as the main toilet were risk factors for cholera infection. There were also several factors that protected against cholera infection, including washing hands after using the toilet and before eating, having a container to store safe water, the presence of soap in kitchen and bathroom, the presence of chlorine bleach and two or more hand washing buckets, a working refrigerator/ice box, and toilet inside or near the house and having a flush toilet. In multivariate analysis, having a working refrigerator/ice box (OR 0.19, 95% CI 0.05-0.70) and Clorox present in the house (OR 0.17, 95% CI 0.04-0.81) were strongly protective against illness. Only 13% (14/106) of case households reported disinfecting household water with chlorine. V. cholerae was isolated from the household water supplies of two controls and one case. During outbreaks of diarrhoeal disease, public health agencies need to aggressively advise affected communities to: disinfect drinking water with clorox bleach, store water in narrow-necked containers, and prepare and store food safely. Health authorities should use multiple strategies inform people about preventive hygiene measures, and implement vaccine campaigns early in outbreaks of cholera. Improvements in sanitation and hygiene are needed to prevent further cholera epidemics in the Pacific.