Epidemiology of Hospitalizations and Deaths from Heat Illness in Soldiers

Robert Carter III; Samuel N. Cheuvront; Jeffrey O. Williams; Margaret A. Kolka; Lou A. Stephenson; Michael N. Sawka; Paul J. Amoroso


Med Sci Sports Exerc. 2005;37(8):1338-1344. 

In This Article

Abstract and Introduction

Purpose: Serious heat illness has received considerable recent attention due to catastrophic heat waves in the United States and Europe, the deaths of high-profile athletes, and military deployments.
Methods: This study documents heat illness hospitalizations and deaths for the U.S. Army from 1980 through 2002. Hospitalization data were obtained from the Total Army Injury Health Outcomes Database (TAIHOD) coded according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). North Atlantic Treaty Organization Standardization Agreement codes were searched for heat injuries in an effort to detect cases that were not found during the ICD-9-CM search.
Results: Five-thousand two-hundred forty-six soldiers were hospitalized, and 37 died due to heat illness. Our results indicate: 1) approximately 60% reduction in hospitalization rates (fewer heat exhaustion cases) over the 22-yr period; 2) fivefold increase in heat stroke hospitalization rates (1.8 per 100,000 in 1980 to 14.5 per 100,000 in 2001); 3) heat stroke cases were associated with dehydration (17%), rhabdomyolysis (25%), and acute renal failure (13%); 4) lower hospitalizations rates among African and Hispanic Americans compared with Caucasians (incidence density ratio, 0.76 [95% confidence interval, 0.71-0.82]; 5) greater rates of hospitalizations and heat strokes among recruits from northern than southern states (incidence density ratio, 1.69 [95% confidence interval, 1.42-1.90]; and 6) greater rates of hospitalizations and heat strokes among women than men (incidence density ratio, 1.18 [95% confidence interval, 1.09-1.27]).
Conclusions: Exertional heat illness continues to be a military problem during training and operations. Whereas the hospitalization rate of heat illness is declining, heat stroke has markedly increased.

Serious heat illness has received considerable recent attention due to catastrophic heat waves in the United States[22] and Europe,[26] the deaths of several high-profile athletes,[18] and recent military deployments to extremely hot environments. Serious heat illness represents a continuum of increasing severity of heat exhaustion to heat stroke.[3] Serious heat illness is often categorized as classic or exertional, with the former primarily observed in sick and compromised populations and the latter primarily observed in apparently healthy and physically fit populations. Because of the populations affected by exertional heat illness, it is believed to be preventable.

Soldiers and athletes perform strenuous physical activity (thus producing high levels of metabolic heat) for extended durations in hot weather and as a result are susceptible to exertional heat illness. The military and civilian communities employ extensive heat mitigation procedures to manage heat strain and reduce the risk of serious exertional heat illness.[8] These heat mitigation procedures include identifying high-risk persons, heat acclimatization, fluid and electrolyte replacement, exercise/rest guidelines, and vigilance. Despite these procedures, heat exposure still results in morbidity and mortality in these relatively young and apparently healthy populations of soldiers and athletes.

Epidemiological studies of exertional heat injury in military populations have focused on specific bases for relatively brief periods and with relatively small populations.[7,9,13] Epidemiological studies of exertional heat injury in athletes have focused only on mortality and do not have sufficient information to calculate incidence.[2,12] The present study examined hospitalizations and deaths from heat illness for the entire active duty U.S. Army during the calendar years of 1980-2002. Specifically, hospitalizations for heat exhaustion and heat stroke were evaluated for incident rates and trends, as well as the role of age, gender, race, and home of record. This represents the largest and most comprehensive epidemiological study of exertional heat injury.