Prior Infection and Prior Heat Illness as Risk Factors for Exertional Heat Stroke

Anecdotal evidence suggests that incidence of exertional heat stroke (EHS) is higher in individuals that have experienced prior infection, prior heat illness, or rhabdomyolysis; however these hypotheses are lacking in scientific validation. To examine these relationships, we searched the Medical Health System Data Repository (MDR) for active duty service members (ADSM) who had at least one EHS during the years of 2008–2014. Incidence was identified using the International Classification of Disease 9 th (ICD‐9) Revision codes from de‐identified electronic medical records. Over this time period, 2,529 ADSM experienced at least one episode of EHS, while 12% of these individuals experienced multiple events (≥2). Within one year preceding EHS, 20% of ADSM suffered a prior heat illness and 9% were diagnosed with rhabdomyolysis. Individuals that suffered a prior heat injury (HI) were 16 times more likely to develop rhabdomyolysis (OR 16.07; 95% CI (11.32–22.81)). Thirty percent of ADSM were also diagnosed with at least one prior infection in the two months preceding EHS or in the seven days following the HI. Further, these individuals were more likely to have suffered a prior HI (OR 1.35; 95% CI (1.03–1.78)). Current medications, immunizations, and allergy diagnosis were then examined as risk factors (RF) for increased susceptibility to EHS. Prescriptions for anti‐inflammatories, anti‐infection, and central nervous system agents were prescribed most often, with 33% of individuals taking at least one medication in the two week time period before EHS. Individuals prescribed anti‐inflammatories (15%) were more likely to have experienced a prior HI (OR 0.36; 95% CI (0.24–0.55)). Interestingly, in the 30 day time period before EHS, 20% of individuals received at least one immunization. Unexpectedly, allergy diagnosis was identified as a risk factor for EHS, occurring in 19.5% of EHS patients. Episode length (EL) (time from clinical admission to release) was used as a gauge of EHS severity. Both prior HI and rhabdomyolysis extended EL (P<.001). Examination of specific organ failure(s) was used to identify tissues most compromised by EHS. Renal failure was most commonly reported, appearing in 30% of EHS cases. Known RFs for EHS such as time of year, elevated body mass index, and advanced age were confirmed. This epidemiological review defines the link between EHS and prior infection, prior heat illness, and rhabdomyolysis and highlighted other lesser known RFs such as immunizations and allergies in ADSM. Author view not official US ARMY or DoD policy.