Ocean climate patterns linked to diarrhea epidemic outbreaks

Spikes in cases of life-threatening diarrhea in young children across the world may be associated with climate conditions linked to the oceans, according to a study which may lead to new early-warning systems to prepare for diarrhea epidemics.

The study, published in the journal Nature Communications, noted that diarrhea is the second leading cause of death in children younger than five years of age in low- and middle-income countries, with 72 percent of the deaths occurring in the first two years of life. The researchers, including those from Columbia University in the US, said El Nino-Southern Oscillation (ENSO) is a coupled ocean-atmosphere system spanning the equatorial Pacific Ocean.

They said the ENSO oscillates in a 3-to-7-year cycle between two extremes, El Nino - warmer ocean temperatures - and La Nina - cooler ocean temperatures, affecting local weather patterns around the world, including temperatures, and rainfall. Analysing the links between ENSO, and cases of diarrhea among children under age five in northeastern Botswana, the scientists found that La Nina is associated with cooler temperatures, increased rainfall, and higher flooding during the rainy season.

Their assessment revealed that La Nina conditions lagged 0-7 months are associated with about a 30 per cent increase in incidence of diarrhea in the early rainy season from December through February. "These findings demonstrate the potential use of the El Nino-Southern Oscillation as a long-lead prediction tool for childhood diarrhea in southern Africa," said study first author Alexandra K. Heaney from the University of California, Berkeley in the US.

"Advanced stockpiling of medical supplies, preparation of hospital beds, and organization of healthcare workers could dramatically improve the ability of health facilities to manage high diarrheal disease incidence," Heaney said. Earlier studies had linked El Nino events to diarrhea outbreaks in Peru, Bangladesh, China, and Japan, but until now the effects of ENSO on diarrheal disease in Africa had been limited to cholera - a pathogen responsible for only a small fraction of diarrheal cases in the continent. However, the researchers said infectious diarrhea is caused by many different pathogens like viruses, bacteria, and protozoa.

They said climatic conditions can have a critical influence on pathogen exposures, particularly those associated with waterborne transmission. Citing an example, the scientists said extreme rainfall events may contaminate drinking water by flushing diarrhea-causing pathogens from pastures and dwellings into drinking water supplies.