Image of thermometer.Researchers have discovered “strong evidence of an association between outdoor heat and respiratory hospitalizations,” according to results posted online ahead of print in the American Journal of Respiratory and Critical Care Medicine.

Investigators looked at 213 urban counties across the country, analyzing measurements of weather and air pollution and reviewing data on Medicare emergency respiratory hospitalizations for more than 30% of the U.S. population aged 65 or older.

For each 10°F increase in daily mean summer temperature, there was an average uptick in respiratory hospitalizations of 4.3%. The increased risk for heat-related hospitalization was 4.7% for COPD and 4.1% for respiratory tract infections; it tended to be higher in counties where summers are typically mild. The association remained after adjusting for air pollution, age, gender or seasonal trends in hospitalization rates and temperature.

“In the largest population of the elderly yet studied, we found strong evidence that short-term exposure to outdoor heat increases the risk of hospitalization for COPD and respiratory tract infections,” said lead author G. Brooke Anderson, PhD, postdoctoral fellow in the Department of Biostatistics at the Johns Hopkins Bloomberg School of Public Health. “This relationship was consistent for men and women and across all age groups studied.”

Researchers believe the projections of increasing temperatures around the globe, along with the increased prevalence of chronic pulmonary disease, make this relationship is of growing concern.