Exertional Heat Stroke at the Vermont City Marathon, 2012 to 2023: High Incidence Despite Spring Season in the Northern United States.

Objective: This study characterizes Vermont City Marathon (VCM) exertional heat stroke (EHS) cases to better understand current EHS trends in US marathon runners.

Design: Retrospective review.

Setting: VCM medical tent for 10 years: 2012 to 2019 and 2022 to 2023.

Patients or participants: In total, 22 224 marathon runners, including 26 patients with EHS.

Independent variables: Demographic, treatment, and environmental data.

Main outcome measures: To characterize patients with EHS and incidence at VCM and compare with other marathons.

Results: Of 22 224 marathon starters, 26 patients with EHS yielded an incidence of EHS of 12/10 000 (0.12%). Compared with all VCM marathon starters, patients with EHS were younger (mean 33 vs 39 years, P = 0.01), but sex did not differ (62% vs 54% male, P = 0.44). All patients with EHS were treated with cold water immersion (CWI) with 100% survival. Cooling rate during CWI was 0.17°C/min and CWI time averaged 16 minutes. Since protocol updates in 2016, only 23% of patients with EHS have required hospital transport. For every 1°C of increasing wet bulb globe temperature (WBGT), EHS incidence at VCM increased by 1.2 cases per 10 000 runners (P = 0.04). Exertional heat stroke at VCM was more frequent than at the Boston Marathon (12 vs 3.7/10 000, P < 0.001), consistent with higher mean WBGT at VCM (20°C vs 14°C, P = 0.04).

Conclusions: This study is the first to characterize patients with EHS at VCM and compare these data to other US marathons. A linear correlation was established between WBGT and EHS incidence. Despite the early season and northerly setting of VCM, EHS was prevalent and important for medical tent preparation. Appropriate EHS treatment was life-saving.