Outbreaks of hand, foot, and mouth disease (HFMD), which causes fever and rashes in young children, typically occur during the summer months, as have historical polio outbreaks in the United States.

Both diseases are caused by different species of enteroviruses, a large genus of RNA viruses. However, the factors behind these seasonal patterns remain somewhat unclear.

A recent study by researchers from Brown University, Princeton University and Johns Hopkins, published in Nature Communications, sheds light on common factors that influence the timing of HFMD and polio outbreaks.

The study suggests that these summer-season outbreaks could have significant impacts on climate change.

“We find that even after controlling for other factors, temperature enhances enterovirus transmission,” said Rachel Baker, the John and Elizabeth Irving Family Assistant Professor of Climate and Health at Brown University and first author of the study. “Importantly, we see a similar size effect for the enterovirus serotypes that historically caused polio and the more recent ones that cause HFMD.”

“Enterovirus outbreaks display clear patterns in space. At higher latitudes, we see large outbreaks of HFMD every two or three years, but closer to the tropics, we see outbreaks up to twice a year — our results are able to capture these large-scale patterns,” said Saki Takahashi, assistant professor of epidemiology at Johns Hopkins University and co-author of the study.

The researchers used epidemiological models to show that temperature and demographic factors, particularly the timing of school semesters, can explain the biannual HFMD outbreaks in southern China. In more northern locations, the temperature effect is more dominant, and the schooling effect is reduced.

“What really matters is the seasonal extent of the climate, that is, the maximum and minimum temperatures,” said Wenchang Yang, associate research scholar in geosciences at Princeton University. “This may have an impact on our thinking about future impacts.”

Using results from 14 different climate models, the authors considered the implications of climate change for enterovirus outbreaks.

“An important finding is the effect of variability,” said Gabriele Vecchi, Knox Taylor Professor of Geosciences and director of the High Meadows Environmental Institute at Princeton University. “The effect of climate variability on disease dynamics has not yet been explored, and this study represents a clear advance in the necessary exploration of this topic.”

The study found that climate change could increase the peak size of enterovirus outbreaks by up to 40%, although the effects vary by location and climate model. Better monitoring of enterovirus circulation could help track these potential impacts. “Serological surveys are important for tracking susceptibility to enteroviruses and other pathogens,” Takahashi said.

The findings highlight the need for improved public health strategies to mitigate the impact of climate change on infectious disease dynamics, especially for vulnerable populations such as young children.