Crowded conditions in developing world megacities can dramatically increase the effect of climate on infectious diseases, say researchers. A study based on 22 years of rotavirus cases in Dhaka, Bangladesh, found infection rates during the monsoon were around ten times higher in the densely populated centre than the quieter periphery.
The virus is the most common cause of diarrhoea in children worldwide and is responsible for more than 400,000 child deaths a year. Rotavirus infection rates in tropical countries are fairly consistent throughout the year with a slight peak in cool seasons, although some studies have found evidence of spikes when river levels are high.
But the study, published in the Proceedings of the National Academy of Sciences, found that a higher baseline of rotavirus infection in the congested core of the city of 15 million appears to make it far more sensitive to flood-driven outbreaks than the suburbs — resulting in a regular second peak during the warm monsoon months.