Risk factors and mortality in relation to heat illness severity

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. 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, as well as to compare the risk factors for mild and severe cases of EHI, as distinguished by core body temperature shortly after the event. Initial fitness was evaluated by a timed run, and slower run-times were found to strongly increase the risk of EHI in both male and female recruits. A 7% increase in risk of EHI per kg/m2 of body mass index (BMI = weight/height2) was observed for male recruits, while among female recruits, BMI was not found to be an important predictor of EHI risk. When the cases of EHI among males were divided into severe (core body temperature ≥ 103.1°F (39.5°C)), and mild (core temperature < 103.1°F (39.5°C)) cases, the best fitting models were somewhat different. 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.; 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 from the Total Army Injury Hospitalization Outcomes Database (TAIHOD) for 3,971 cases of HI. Because data do not exist on the full cohort of Army personnel, it was necessary to use a reference cause of hospitalization as a comparison group. We used 17,233 referent cases of appendicitis (APX). Vital status of these cases was determined through the National Death Index (NDI), and 115 HI and 585 APX cases were found to have died. Male and female HI cases had a 40% increased rate of all-cause mortality compared to APX cases. (Abstract shortened by UMI.)...