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El Niño and the shifting geography of cholera in Africa

  1. Justin Lesslera,1
  1. aDepartment of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205;
  2. bDepartment of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556;
  3. cEck Institute for Global Health, University of Notre Dame, Notre Dame, IN 46556;
  4. dDepartment of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218;
  5. eDivision of Foodborne, Waterborne and Environmental Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30329;
  6. fDepartment of Pandemic and Epidemic Diseases, World Health Organization, 1211, Geneva, Switzerland;
  7. gEpicentre, 75012 Paris, France;
  8. hDepartment of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205;
  9. iMédecins Sans Frontières, 75011 Paris, France

  1. Edited by Andrea Rinaldo, Laboratory of Ecohydrology (ECHO/IIE/ENAC), Ecole Polytechnique Federale Lausanne, and approved March 8, 2017 (received for review October 18, 2016)

Significance

In the wake of the 2015–2016 El Niño, multiple cholera epidemics occurred in East Africa, including the largest outbreak since the 1997–1998 El Niño in Tanzania, suggesting a link between El Niño and cholera in Africa. However, little evidence exists for this link. Using high-resolution mapping techniques, we found the cholera burden shifts to East Africa during and following El Niño events. Throughout Africa, cholera incidence increased three-fold in El Niño-sensitive regions, and 177 million people experienced an increase in cholera incidence. Without treatment, the case fatality rate can reach 50%, but accessible, appropriate care nearly eliminates mortality. Climatic forecasts predicting El Niño events 6–12 mo in advance could trigger public health preparations and save lives.

Abstract

The El Niño Southern Oscillation (ENSO) and other climate patterns can have profound impacts on the occurrence of infectious diseases ranging from dengue to cholera. In Africa, El Niño conditions are associated with increased rainfall in East Africa and decreased rainfall in southern Africa, West Africa, and parts of the Sahel. Because of the key role of water supplies in cholera transmission, a relationship between El Niño events and cholera incidence is highly plausible, and previous research has shown a link between ENSO patterns and cholera in Bangladesh. However, there is little systematic evidence for this link in Africa. Using high-resolution mapping techniques, we find that the annual geographic distribution of cholera in Africa from 2000 to 2014 changes dramatically, with the burden shifting to continental East Africa—and away from Madagascar and portions of southern, Central, and West Africa—where almost 50,000 additional cases occur during El Niño years. Cholera incidence during El Niño years was higher in regions of East Africa with increased rainfall, but incidence was also higher in some areas with decreased rainfall, suggesting a complex relationship between rainfall and cholera incidence. Here, we show clear evidence for a shift in the distribution of cholera incidence throughout Africa in El Niño years, likely mediated by El Niño’s impact on local climatic factors. Knowledge of this relationship between cholera and climate patterns coupled with ENSO forecasting could be used to notify countries in Africa when they are likely to see a major shift in their cholera risk.

Footnotes

  • ↵1To whom correspondence should be addressed. Email: justin{at}jhu.edu.

  • Author contributions: S.M.M., A.S.A., B.F.Z., E.D.M., F.J.L., and J.L. designed research; S.M.M., A.S.A., B.F.Z., E.D.M., F.J.L. and J.L. conceived this study; S.M.M., A.S.A., B.F.Z., J.B., D.L., A.H., H.M., F.J.L., D.O., and J.L. performed research; S.M.M., A.S.A., B.F.Z., D.L., A.H., H.M., F.J.L., D.O., and J.L. contributed to the collection, assembly, and entry of data; S.M.M., A.S.A., B.F.Z., and J.L. analyzed data; and S.M.M., A.S.A., and J.L. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1617218114/-/DCSupplemental.

Freely available online through the PNAS open access option.

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    This Week in PNAS: In This Issue PNAS 2017 114 (17) 4267; doi:10.1073/iti1717114