This article is more than 5 years old. Information may no longer be current.
El Niño causes geographical shift in cholera incidence in Africa
El Niño impacts the distribution of cholera in Africa, researchers said, because cases increase in East Africa by up to 50,000 and decrease in other parts of the continent during years in which the weather phenomenon occurs.
Predicting the regional shift in disease prevalence with El Niño’s arrival can help officials prepare for it and save lives, they wrote in Proceedings of the National Academy of Sciences.
“We usually know when El Niño is coming 6 to 12 months before it occurs,” researcher Justin Lessler, PhD, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, said in a news release. “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% to next to nothing.”
El Niño increases rainfall in East Africa and decreases it in the drier areas of the continent’s north and south. Heavier rainfall can overwhelm sewer systems and contaminate drinking water.
The researchers mapped estimated cholera prevalence in 20 × 20 km areas throughout Africa. They used more than 17,000 yearly cholera observations made between 2000 and 2014 in more than 3,000 locations ranging from entire countries to specific neighborhoods.
They found little difference between El Niño years and non-El Niño years in cholera prevalence in Africa overall, as the mean numbers of cases were 215,546 and 209,791, respectively.
However, there were regional differences, the researchers said. For example, in East Africa — excluding Madagascar — there was a mean of 48,670 more cases of cholera during El Niño years. Conversely, Southern Africa had 31,598 fewer cholera cases during El Niño years.
The area from the Horn of Africa to Mozambique had the largest increase in expected cholera incidence during El Niño years, researchers said. There and in other sensitive areas in Africa, cholera incidence increased in those years from 1.1 per 10,000 population to 3.3 per 10,000. That translates to nearly 55,000 more cases during El Niño years than in other years in those areas.
The 14-year study period included four El Niño events, two characterized as weak and two as moderate. To determine whether their results bear out in a longer time frame, the researchers compared their data with those reported in individual countries to WHO dating back to 1980.
They found that the data showed that “increases in cholera incidence are concentrated in continental East Africa, specifically Tanzania and Kenya, where El Niño events are associated with increased rainfall and generally wet conditions.”
The patterns identified in the study can be used to predict outbreaks and help apply the necessary tools to fight them, the researchers concluded.
“Because effective case management dramatically decreases mortality in cholera outbreaks, and new control tools (eg, oral cholera vaccines) may prevent, or at least limit, outbreaks,” they wrote, “the ability to step up surveillance, preparedness and response when local risk is high can have a significant impact on saving lives.” – by Joe Green
Disclosure: The researchers report no relevant financial disclosures.