Researchers are reporting a link between a climate phenomenon know as El Nino and the number of cholera cases in eastern Africa. Predicting when there’s going to be an El Nino event could improve public health preparedness.
El Ninos are a global climate phenomenon that occurs at irregular times, approximately every two to seven years.
During an El Nino, surface ocean temperatures in the eastern Pacific off the coast of South America become warmer than usual. The warming trend begins around Christmas time.
The following year, in the fall, sea surface temperatures also warm, if somewhat less, in the western Pacific, leading to extreme weather events like flooding and droughts, conditions that are ripe for cholera outbreaks.
Approximately 177 million people reside in areas where the incidence of cholera increases during El Nino.
But there’s been scant evidence of El Nino’s health impact in Africa.
A study published in the Proceedings of the National Academy of Sciences found the incidence of cholera increased in countries in East Africa.
“Because they can either lead to surface flooding that washes contamination into drinking water in areas where there’s open defecation,” said epidemiologist Sean Moore, who led the study. “It also can lead to overflowing of sewer systems in urban areas which again can lead to contamination of drinking water.”
There are approximately 150,000 cases of cholera per year, mostly in sub-Saharan Africa, according to Moore, an epidemiologist at Johns Hopkins School of Public Health in Baltimore.
But during El Ninos, researchers found the incidence swelled by some 50,000 cholera cases in eastern Africa, although the overall number of cases on the continent did not change — for reasons that are not completely understood, said Moore.
Patterns of shift in the number of cholera cases were measured during El Ninos between the years 2000 and 2014. There also were 30,000 fewer cases reported in southern Africa during El Nino years compared to non-El Nino years, researchers found..
Scientists also saw a slight increase in the number of cholera cases in areas hit by drought due to El Nino.
Moore said that’s because when water becomes scarce, available drinking water can become contaminated by bacteria in human waste.
Without treatment, mortality rates from cholera can climb as high as 50 percent.
To the extent that the climate phenomenon can be predicted six to 12 months ahead of time, Moore said public health officials can prepare for outbreaks, which tend to occur early on.
“An advance warning could, even if it doesn’t prevent outbreak, it could at least prevent the deaths that tend to occur during the early part of an outbreak,” he said.
With oral rehydration therapy, Moore said the risk of death from cholera drops to 1 percent. He said there are now cheap cholera vaccines that could be used to prevent the disease when it’s known that an area is going to be hit by an El Nino.