Trends and Regional Variation in Heat-Related EMS Encounters in the US

Heat-related emergencies are increasing in the United States (U.S.), but little is known about trends in prehospital heat-related encounters. This study examines temporal and geographic trends in prehospital heat-related encounters and assesses demographic and clinical factors associated with these heat-related encounters.

We used an observational study design and a retrospective analysis of the 2019-2023 National Emergency Medical Services Information System (NEMSIS) databases. We described the characteristics of heat-related encounters and compared the rates of heat-related complaints by year. Comparing 2019 to each year from 2020-2023, we used logistic regression to evaluate the odds of heat-related complaints. We then repeated these regressions for each U.S. census division to evaluate for regional variation in the trends of heat-related complaints.

We included 120,181,275 non-heat-related encounters and 478,666 heat-related encounters. Compared to non-heat-related encounters, heat-related encounters involved younger patients, more males, and higher rates of tachycardia and hypotension. The odds of heat-related encounters increased in 2023 compared to 2019 (odds ratio (OR) 1.04, (1.03-1.05)), but other years were similar. There was significant regional variation in heat-related encounters between Census Divisions, though. The largest increases were: 2020 - Mountain (OR 1.13 (1.09-1.16)); 2021 - Pacific (OR 1.25 (1.22-1.29)); 2022 - Mountain (OR 1.23 (1.19-1.26)) and West South Central (OR 1.19 (1.17-1.22)); 2023 - West South Central (OR 1.54 (1.51-1.57)) and West North Central (OR 1.18 (1.14-1.22)) and Mountain (OR 1.29 (1.25-1.33)).

While national odds and proportions of heat-related prehospital encounters have risen slightly in 2023 compared to 2019, certain geographic regions have experienced far greater increases. Further research is needed to identify vulnerabilities and optimize emergency response strategies.