Original Contributions


, Volume 4, Issue 1, pp 52-62

First online:

Cholera Seasonality in Madras (1901–1940): Dual Role for Rainfall in Endemic and Epidemic Regions

  • Diego Ruiz-MorenoAffiliated withDepartment of Ecology and Evolutionary Biology, University of Michigan Email author 
  • , Mercedes PascualAffiliated withDepartment of Ecology and Evolutionary Biology, University of Michigan
  • , Menno BoumaAffiliated withDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, University of London
  • , Andrew DobsonAffiliated withDepartment of Ecology and Evolutionary Biology, Princeton University
  • , Benjamin CashAffiliated withCenter for Ocean–Land–Atmosphere Studies

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The seasonality of cholera and its spatial variability remain unexplained. Uncovering the role of environmental drivers in these seasonal patterns is critical to understand temporal variability at longer time scales, including trends and interannual variability. Rainfall has been proposed as a key driver of the seasonality of cholera. To address this hypothesis, we examine the association between rainfall and cholera in both time and space using the extensive historical records for the districts of Madras in former British India (1901–1940). We show the existence of two main spatial clusters that differ not just in the effect of rainfall but also in the seasonal pattern and frequency of periods with and without cholera mortality. The results support a model of cholera seasonality with two different routes of transmission: one is enhanced by increasing rainfall (in areas with abundant water), the other is buffered by increasing water. We discuss how the dual nature of the influence of rainfall creates different temporal patterns in regions where cholera is either “endemic” or “epidemic.”


Cholera endemic cholera epidemic cholera rainfall