Under the weather

Scientists say a change in temperature could play a role in spreading childhood diarrhoea

Published: Sunday 30 April 2000

the effects of climatic phenomenon on human health may be more widespread that previously considered. Recent research, led by the Johns Hopkins School of Public Health, Baltimore, has now linked El Nio with an increase in childhood diarrhoea. This comes in the wake of scientists linking El Nio with illnesses such as malaria and cholera.

The study also suggests - for the first time - that gradual temperature increases caused by global warming could engineer outbreaks of diarrhoea in children of developing nations. The disease is known to kill around three million children annually under the age of five worldwide.

Outbreaks of the disease are generally associated with the warmer seasons but, until now, experts were unaware of the fact that a change in temperature could play a role in its spread. The study of 57,331 children in Lima, Peru, showed that the rise in diarrhoea cases between 1993 and 1997 was linked to even small temperature rises, regardless of whether it was summer or winter. The effect was greater in winter, even though the weather was cooler.

The study, published in a recent issue of The Lancet medical journal, found that for every 1 c hotter than normal, 8 per cent more children were treated for diarrhoea. The study found the findings were similar for the 1997-1998 El Nio period. The number of children treated each day that winter was double that of the corresponding period during years when El Nio had not occurred. El Nio, which involves the equatorial waters in the Pacific warming up, creating unusual weather patterns around the world, increased winter temperatures in Lima by about 4 c . A similar increase in temperatures brought on by El Nio in the summer was still connected to more diarrhoea than usual, but the effect was not as strong.

"The potential effect of global warming on disease is controversial,'' said William Checkley of Johns Hopkins, who led the study. This study suggests there may be something to it for diarrhoea. It's plausible the researchers' findings could apply in countries other than Peru, said Tony McMichael, epidemiology professor at the London School of Hygiene and Tropical Medicine who studies the effects of climate on disease. "In general, a large proportion of infectious disease agents are very sensitive to slight changes in climate,'' said McMichael. "This would give us a reasonable indication of how diarrhoea agents react to changes in temperature in general, whether in water or in food.''

Checkley said the stronger effect in winter could be due to the fact that the types of diarrhoea common in winter and summer are different. In hot weather, diarrhoea caused by bacteria or parasites is more likely. Cooler temperatures appear to enhance the transmission of viral diarrhoea, he said.

When the winters are warmer than normal, it could be that children are exposed to more sources of diarrhoea, including the bacterial and parasite sort. El Nio also may prompt diarrhoea-promoting behaviour more common in the summer, such as more demand for water, the study said.

Olivier Fontaine, a diarrhoea expert at the World Health Organization, said the observed link makes sense. "This may be useful for developing strategies to combat the disease by intervening to prevent it,'' Fontaine said. "If we can predict a change in the weather, such as when El Nio cycles around, we could have all the interventions in place before the weather changes.''

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