Population vulnerability to biannual cholera outbreaks and associated macro-scale drivers in the Bengal Delta

Abstract

The highly populated floodplains of the Bengal Delta have a long history of endemic and epidemic cholera outbreaks, both coastal and inland. Previous studies have not addressed the spatio-temporal dynamics of population vulnerability related to the influence of underlying large-scale processes. We analyzed spatial and temporal variability of cholera incidence across six surveillance sites in the Bengal Delta and their association with regional hydroclimatic and environmental drivers. More specifically, we use salinity and flood inundation modeling across the vulnerable districts of Bangladesh to test earlier proposed hypotheses on the role of these environmental variables. Our results show strong influence of seasonal and interannual variability in estuarine salinity on spring outbreaks and inland flooding on fall outbreaks. A large segment of the population in the Bengal Delta floodplains remain vulnerable to these biannual cholera transmission mechanisms that provide ecologic and environmental conditions for outbreaks over large geographic regions.

Figure 1.

A, District-wise population density map of Bangladesh, showing surveillance areas used in this study and location of major rivers in the region. B, Schematic of conceptual model setup for simulation of estuarine salinity and flood inundation. GBM = Ganges-Brahmaputra-Meghna.

Figure 2.

Comparison of normalized A, mean monthly cholera incidence; B, mean spring incidence anomaly; and C, mean fall incidence anomaly for selected locations, Bangladesh.

Figure 4.

Monthly cholera incidence in Dhaka, Matlab, and Bakerganj, Bangladseh, and Kolkata, India, and high and low estuarine salinity in southwestern Bangladesh, 1988–2007.

Figure 3.

Mean seasonal cholera incidence and stream flow anomaly in Bengal Delta for A, dry and B, wet seasons, Bangladesh, 1998–2007.

Figure 5.

Monthly cholera incidence in Dhaka, Matlab, Bakerganj, Bangladesh, and Kolkata, India, and high and low flood inundation in central and northeastern Bangladesh, 1988–2007.