Far more children were treated for diarrhoea in winter, for instance when the mean difference in daily ambient temperature averaged just over 4 degrees centigrade. This does not happen during normal years.
Diarrhoea kills three million children under five every year.
Hot weather favours bacteria such as E.coli and mosquitoes thrive too. Cool weather enhances the transmission of viral diarrhoea. As well as raising the temperature in Peru, it can bring storms to the California coast, droughts to Australia and both heavy rainfall and drought to southern Africa. Even so, understanding weather effects such as this one is important for health service planning, and it could be even more important still, if global climate change occurs as projected.