Seasonality of cholera from 1974 to 2005: a review of global patterns

Michael Emch¹^,2 , Caryl Feldacker²^,3 , M Sirajul Islam⁴ and Mohammad Ali⁵

¹Department of Geography, University of North Carolina-Chapel Hill, USA

²Carolina Population Center, University of North Carolina-Chapel Hill, USA

³Department of Health Behavior and Health Education, University of North Carolina-Chapel Hill, USA

⁴ICDDR, B: Centre for Health and Population Research, Bangladesh

⁵International Vaccine Institute, Korea

author email corresponding author email

International Journal of Health Geographics 2008, 7:31doi:10.1186/1476-072X-7-31


Published:	20 June 2008

Abstract

Background

The seasonality of cholera is described in various study areas throughout the world. However, no study examines how temporal cycles of the disease vary around the world or reviews its hypothesized causes. This paper reviews the literature on the seasonality of cholera and describes its temporal cycles by compiling and analyzing 32 years of global cholera data. This paper also provides a detailed literature review on regional patterns and environmental and climatic drivers of cholera patterns.

Data, Methods, and Results

Cholera data are compiled from 1974 to 2005 from the World Health Organization Weekly Epidemiological Reports, a database that includes all reported cholera cases in 140 countries. The data are analyzed to measure whether season, latitude, and their interaction are significantly associated with the country-level number of outbreaks in each of the 12 preceding months using separate negative binomial regression models for northern, southern, and combined hemispheres. Likelihood ratios tests are used to determine the model of best fit. The results suggest that cholera outbreaks demonstrate seasonal patterns in higher absolute latitudes, but closer to the equator, cholera outbreaks do not follow a clear seasonal pattern.

Conclusion

The findings suggest that environmental and climatic factors partially control the temporal variability of cholera. These results also indirectly contribute to the growing debate about the effects of climate change and global warming. As climate change threatens to increase global temperature, resulting rises in sea levels and temperatures may influence the temporal fluctuations of cholera, potentially increasing the frequency and duration of cholera outbreaks.