Environmental influences on cholera outbreaks in Bangladesh and Vietnam: Implications for prevention and prediction

Cholera is a major problem in many parts of the world, and it is endemic in Bangladesh and Vietnam. Responding to cholera is effective in preventing deaths and slowing the spread of infection, but a prediction model could reduce the scope and duration of outbreak through effective and timely vaccination. Research into the indirect causes of cholera indicates that environmental factors such as sea surface temperature and ocean chlorophyll concentration play a role in cholera outbreaks. This investigation uses 25 years of data to examine the environmental drivers of cholera infection in Bangladesh and Vietnam using population- and spatially-derived variables. For Bangladesh, ordered probit models are utilized to examine the associations between the severity of monthly cholera outbreaks and environmental variables for full year and peak season models. In the two sites in Vietnam, probit models are used to determine the associations between environmental variables and cholera. All variables are aggregated by month and reflect monthly mean values. In Bangladesh, the prediction model suggests that increases in ocean chlorophyll concentration may play a larger role in influencing cholera severity than increases in sea surface temperature. The model also suggests that the effects of both sea surface temperature and ocean chlorophyll concentration have a lag effect. In Vietnam, ocean chlorophyll appears to not play a role; current and lag effects of sea surface temperature and river height appear associated with outbreaks. These within and between site comparisons and prediction models are applicable for development of an early warning system for cholera.