Risk Factors and Mortality in Relation to Heat Illness Severity

Abstract

Abstract : Study 1. A case-crossover study was conducted in male and female Marine Corps recruits in basic training at Marine Corps Recruit Depot (MCRD), Parris Island, SC to investigate the effects of alternative indices of heat exposure on exertional heat illness (EHI) risk. Weather measurements were obtained for 2,069 cases of EHI identified in this population during 1979-1997. As expected, the risk for developing EHI increased with increasing wet bulb globe temperature (WBGT), which is the standard heat index used by the Marine Corps. EHI risk was found to be associated not only with the WBGT at the time of the event, but by the previous day's average WBGT as well. This result suggests evidence of a cumulative effect of previous day's heat exposure in these Marine recruits at MCRD. Study 2. A matched case control study was conducted to investigate the effects of fitness and conditioning on EHI risk, a well as to compare the risk factors for mild and severe cases of EHI, as distinguished by core body temperature shortly after the event. Physical fitness, anthropometric and physiological measurements were acquired for 660 EHI cases identified in this population for the period 1988-1996 and matched to 1,723 controls by initial training platoon. For severe cases, BMI and initial run-time did not have independent effects, but instead showed a less-than-additive effect at high levels of each. In contrast, BMI and run-time appeared to have independent effects on risk of mild EHI. Study 3. A cohort mortality study was carried out among male and female U.S. Army personnel hospitalized for heat illness (HI) at U.S. Army hospitals during 1971-2000. Hospitalization records were obtained for 3,971 cases of HI and 17,233 referent cases of appendicitis (APX). Male and female HI cases had a 40% increased rate of all-cause mortality compared to APX cases.