Quantifying Relative Importance Of Risk Factors For Exertional Heat Illness During Military Training

There are numerous risk factors associated with increased risk of exertional heat illness (EHI). However, the prevalence and relative importance of individual factors in a military setting are unknown. PURPOSE: The purpose of this study was to identify the most frequently occurring risk factors in EHI casualties presenting to Martin Army Community Hospital (MACH), Ft. Moore, GA. Additionally, we determined the number of risk factors present for each individual subject. METHODS: Active-duty service members who were transported to MACH ED and diagnosed with heat exhaustion (HE), heat injury (HI; HE plus evidence of end-organ damage) or exertional heat stroke (EHS) were eligible for inclusion. Volunteers provided written, informed consent, and completed a demographic and risk factors questionnaire. Risk factors included BMI, hydration status, aerobic fitness, race, acclimatization status, event type, clothing worn, load carried, sickle cell trait status, supplement use, and concurrent/pre-existing illness. The questionnaire was completed within 24 hours of the EHI event, and a member of the study team was available to clarify questions. RESULTS: There were 141 heat casualties (61 HE, 19 HI, 61 EHS), comprised of 126 men and 15 women (weight 81.7 ± 13.6 kg, height 1.76 ± 0.09 m), 86 of whom were junior enlisted, 13 Non-commissioned officers and 42 company grade officers. The most frequently occurring risk factors for all class of heat illness were BMI (>25 kg/m2), lack of acclimatization (<30 days at Fort Moore), clothing (fatigues vs physical fitness uniform) and load carriage, although the rank order and relative proportions varied by diagnosis. On an individual basis, HE and HI casualties had 4 ± 2 risk factors while EHS had 3 ± 1 risk factors. There was 1 HE and 1 EHS with no identifiable risk factors. Fifty-five of 61 EHS casualties occurred during foot march or run events. CONCLUSIONS: Acclimatization, BMI, load carriage and clothing were identified as the most frequent factors associated with EHI. This suggests that these factors should receive particular attention in development of targeted prevention strategies to reduce EHI. The low frequency of other risk factors suggests that leaders are effectively implementing prevention strategies and/or those risk factors are less important in this population. Military Operational Medicine Research Program