Background: The incidence of cholera in Bangladesh shows clear seasonality,
suggesting that weather factors could play a role in its epidemiology. We estimated
the effects of rainfall on the incidence of cholera in Dhaka, Bangladesh.
Methods: We examined time-series patterns of the weekly number of hospital visits
due to cholera in relation to weekly rainfall from 1996 to 2002. We used Poisson
regression models, adjusted for seasonal variation, between-year variation, public
holidays and temperature. The role of river level on the rainfall-cholera relationship
was also examined by incorporating river-level terms into the models.
Results: The weekly number of cholera cases increased by 14% (95 % confidence
interval = 10.1% - 18.9%) for each 10-millimeter increase above the threshold of 45
millimeters for the average rainfall, over lags 0−8 weeks. Conversely, the number of
cholera cases increased by 24% (10.7% - 38.6%) for a 10-millimeter decrease below
the same threshold of average rainfall, over lags 0−16 weeks. River level partly
explained the association between high rainfall and the number of cholera cases.
Conclusions: The number of cholera cases increased with both high and low rainfall
in the weeks preceding hospital visits. These results suggest that factors associated
with river level are on the causal pathway between high rainfall and incidence of
cholera.