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El Niño raises cholera risk in East Africa, researchers find

Children collect water in Uwiro Village, Tanzania. (credit: Tom Murphy)

Last year, Tanzania suffered from its largest cholera outbreak in a decade. New research helps identify the culprit – El Niño.

By causing more rainfall in parts of Africa, some 177 million people experienced a threefold increase in cholera cases due to El Niño. That means 50,000 more cholera cases compared to other years.

Cholera can have a fatality rate as high as 50 percent when treated too late. Showing the connection between the global weather event and the waterborne disease is good news. It makes it easier for governments to mobilize efforts to prevent outbreaks and save lives, said study leader Justin Lessler of Johns Hopkins University.

“We usually know when El Niño is coming six to 12 months before it occurs,” he said in a statement. “Knowing there is elevated cholera risk in a particular region can help reduce the number of deaths that result. If you have cholera treatment centers available, fast, supportive care can reduce the fatality rate from cholera from as high as 30 percent to next to nothing.”

East Africa is at most risk because it generally experiences a significant increase in rainfall during El Niño years. Lessler and his fellow researchers analyzed cholera outbreaks between 2000 and 2014. They compared trends between regular and El Niño years to determine any changes. Total cholera cases on the continent did not change year-to-year, but the location of outbreaks shifted when there was an El Niño.

Cases fell in southern Africa by 30,000 during an El Niño, due to drier conditions. A smaller reduction occurs in parts of west Africa as well. The warmer and wetter weather that arrives in East Africa makes it easier for cholera to spread. The researchers point out the link between cholera and access to safe drinking water. Flooding caused by increased rains can contaminate drinking water.

It makes sense that unusually high rain levels contribute to more waterborne diseases. The increased rains exacerbated the stress on Tanzania in 2015 when a surge of people fled Burundi and a cholera outbreak ensued. But this is the first time that the connection between El Niño and cholera is shown.

“Linking these outbreaks to El Niño events and increased rainfall improves our understanding of the environmental conditions that promote cholera transmission in the region and will help predict future outbreaks,” Sean Moore, a co-author of the study, said in a statement.

The findings are more evidence of the impacts of climate change on the lives of the world’s most vulnerable people. Researchers in 2014 reported that the greenhouse gases causing global warming also contribute to more El Niño events. Projected surface warming over the eastern equatorial Pacific contributes to the increased occurrence.

The strong 2015-16 El Niño not only increased cholera cases in Tanzania, but it caused southern Africa’s worst drought in 35 years. More than 18 million people were affected. Rains returned earlier this year meaning the region went two years with poor crop harvests.

Relief may not last for long. The odds of El Niño returning later in 2017 is increasing, according to the Climate Prediction Center. Depending on the strength, it potentially means more rains for East Africa, which is in the middle of its own drought, and the return of dry weather for the western and southern parts of the continent. If the lessons from the new research are applied, it may be possible to prevent or respond quickly to cholera outbreaks.


About Author

Tom Murphy

Tom Murphy is a New Hampshire-based reporter for Humanosphere. Before joining Humanosphere, Tom founded and edited the aid blog A View From the Cave. His work has appeared in Foreign Policy, the Huffington Post, the Guardian, GlobalPost and Christian Science Monitor. He tweets at @viewfromthecave. Contact him at tmurphy[at]