Outdoor Heat Linked to Respiratory Disorders in the Elderly

Joe Barber Jr, PhD

March 08, 2013

Increases in outdoor temperature may increase the risk for emergency hospitalizations resulting from respiratory disorders among the elderly in the United States, according to the findings of a large, population-based study.

G. Brooke Anderson, PhD, from the Johns Hopkins School of Medicine in Baltimore, Maryland, and colleagues published their findings online March 8 in the American Journal of Respiratory and Critical Care Medicine.

Previous studies have shown a link between increasing outdoor temperature and risk of mortality for the elderly population. However, the researchers note that current research on the association between heat and respiratory hospitalizations has 2 major limitations. "First, this relationship has not been adequately studied worldwide to confidently identify a consistent link between respiratory hospitalizations and heat," the authors write.

"Second, outside of California and New York, little research has been done in the United States."

Therefore, the authors investigated hospitalization rates in relation to outdoor temperature for approximately 12.5 million Medicare recipients in 213 urban counties between 1998 and 2008. The researchers found that each 5.6°C increase in mean summer temperature was associated with a 4.3% (95% posterior interval [PI], 3.8% - 4.8%) increase in the relative risk (RR) for respiratory hospitalizations.

The relationships between rising temperature and increased odds of respiratory hospitalizations held for chronic obstructive pulmonary disease (RR, 4.7%; 95% PI, 3.9% - 5.5%) and respiratory tract infections (RR, 4.1%; 95% PI, 3.4% - 4.7%). In addition, the magnitude of risk for respiratory hospitalization associated with a 5.6°C increase in temperature was similar for men (RR, 4.3%; 95% PI, 3.6% - 5.0%) and women (RR, 4.4; 95% PI, 3.7% - 5.1%).

Moreover, no difference in risk was noted among the different age groups (65 - 74 years old: RR, 4.8% [95% PI, 4.0% - 5.6%]; 75 - 84 years old: RR, 4.2% [95% PI, 3.5% - 4.9%]; ≥85 years old: RR, 4.2% [95% PI, 3.2% - 5.2%]). For counties with a mean summer temperature that was 5.6°C cooler than the national average, the elderly had a 1.4% higher RR (95% PI, 0.4% - 2.3%) of respiratory hospitalization than the national RR.

The investigators note that the association between outdoor temperature and hospitalization risk did not change after adjusting for air pollution, age, gender, or seasonal trends in hospitalization rates and temperature. Although the association was strongest on the day of heat exposure, the investigators note that the association persisted for the following day as well.

"In summary, in a 10-year study of Medicare respiratory hospitalizations and outdoor heat in 213 US counties, we found risk of respiratory hospitalization significantly increased with daily outdoor heat," the authors write. "Heat-related respiratory hazards are likely to increase in the future with increasing prevalence of respiratory conditions and rising temperatures from climate change."

Dr. Anderson and one coauthor received study funding from the National Institute for Environmental Health Sciences. Three other coauthors received funding from the National Institute for Environmental Health Sciences and US Environmental Protection Agency. One coauthor received funding from the National Institutes of Health.

Am J Respir Crit Care Med. Published online March 8, 2013.