Hospital Admissions During Heat Waves Are Cause-Specific

A new study reveals that a handful of potentially serious disorders significantly increase the risk of hospitalization during periods of extreme heat.

Researchers at Harvard School of Public Health (HSPH; Boston, MA, USA) and Brigham and Women’s Hospital (Boston, MA, USA) conducted a study that analyzed 127 billion daily hospitalizations in a population of 23.7 million Medicare beneficiaries between 1999 and 2010, covering 1,943 counties in the United States with at least five summers of near-complete daily temperature data. Heat-wave periods were matched to non-heat-wave periods, with daily charting of cause-specific hospitalization rates by principal discharge diagnosis codes.

The results showed that older Americans were two-and-a-half times more likely to be hospitalized from heat stroke during heat waves than on non-heat-wave days. Extreme heat also put the elderly at 18% greater risk of being hospitalized for fluid and electrolyte disorders; 14% greater risk for renal failure; 10% greater risk for urinary tract infections; and 6% greater risk for sepsis. Conversely, risk of hospitalization for congestive heart failure (CHF) was lower. Risks were generally highest on the heat wave day, but remained elevated for up to five subsequent days. The study was published on December 23, 2014, in the Journal of the American Medical Association (JAMA).

“An innovative aspect of this work is that rather than preselect a few individual diseases to examine, we considered all possible causes of hospital admission during heat waves in order to characterize the effects of heat on multiple organ systems,” said lead author Professor of Biostatistics Francesca Dominici, PhD, of HSPH.

Heat wave periods, as defined by the World Meteorological Organization (Geneva, Switzerland), is when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C, the normal period being 1961–1990. Another definition is as two or more consecutive days with temperatures exceeding the 99th percentile of the area. The 1930s are remembered as the driest and warmest decade in the US (the Dust Bowl years), and the summer of 1936 was the most widespread and destructive heat wave to occur in the Americas in centuries.

Related Links:
Harvard School of Public Health
Brigham and Women’s Hospital