Hydrology and Human Health: Predicting Cholera Outbreaks using Remote Sensing Data

Cholera bacteria survive and thrive in two distinctively different environments: the micro- and the macro-environmental processes that vary over a range of spatial and temporal scales. While micro-environmental conditions are necessary for maintaining epidemic conditions, macro-environmental conditions set the stage for initial outbreak and endemicity of the disease. As macro-environmental processes provide natural ecological niche for V. cholerae and there is powerful evidence of new biotypes emerging, it is unlikely that cholera will be fully eradicated, a condition which necessitates exploration of alternate means to develop prediction mechanism for cholera outbreaks. Satellite remote sensing data provides reliable estimates of plankton abundance through chlorophyll content which then can be used to understand cholera - chlorophyll relationships. However, the functional nature of association of cholera incidence with chlorophyll and its predictive capabilities are not well understood. Here we show that cholera outbreaks in Bengal Delta can be predicted two to three months in advance with an overall prediction accuracy of greater than 80% using combination of satellite derived chlorophyll and air temperature. Such high prediction accuracy is achievable because the two seasonal peaks of cholera in Bengal Delta are controlled by two distinctive macro-environmental processes. We have found that interannual variability of pre- monsoonal cholera outbreaks is intricately linked with coastal plankton through a cascade of hydro-coastal processes. Post- monsoonal cholera outbreaks, on the other hand, are related with wide spreading flooding and subsequent breakdown of the sanitary conditions. Our results demonstrate that satellite data, with a careful choice of space and time scales, can be very effective to develop a cholera prediction model for the Bengal delta with several months lead time. We anticipate that our modeling framework will provide essential lead time for developing appropriate cholera mitigation strategies for other cholera endemic regions of the world.