TOPLINE: 

Emergency medical service (EMS) activations for heat-related cases in the US increased by 65% from 2019 to 2024. Middle-aged adults (35-64 years) and areas with incomes of $25,000-$35,000 showed faster increases in heat-related EMS calls than in non-heat-related calls.

METHODOLOGY:

• Researchers conducted a cross-sectional analysis of EMS agencies reporting data annually from 2019 through 2024, using data from the National Emergency Medical Services Information System.
• Heat-related conditions were identified using clinician‑entered diagnostic codes for heat illness, and incidence rates of heat-related and non-heat-related EMS activations were calculated.
• The outcomes were population‑adjusted changes in heat‑related EMS rates over time and differences between heat-related and non‑heat-related rates across age groups, sexes, racial/ethnic groups, income levels, and regions.

TAKEAWAY:

• The rates of population-adjusted heat-related EMS activations increased by 65%, whereas those of non-heat-related activations increased by 69% between 2019 and 2024. Overall, the rates of heat-related EMS activations increased at a slower pace than those of non-heat-related activations (Ratio of rate ratios [RRR], 0.98; P < .001).
• However, the rates of heat-related EMS activations increased faster than those of non-heat-related activations among adults aged 35-54 years (RRR, 1.07; P < .001) or 55-64 years (RRR, 1.05; P = .007) and in areas with median incomes of $25,000-$35,000 (RRR, 1.11; P = .02). Faster relative increases were also observed in the Mountain (RRR, 1.13; P < .001) and West South-Central (RRR, 1.11; P < .001) divisions.
• The rates of heat-related activations increased more slowly than those of non-heat-related activations among male individuals (RRR, 0.96; P < .001), children and adolescents aged 0-17 years (RRR, 0.91; P < .001), and most racial and ethnic groups, including Black (RRR, 0.91; P < .001), Hispanic (RRR, 0.95; P = .02), Asian (RRR, 0.87; P = .03), and White (RRR, 0.92; P < .001) individuals.
• Higher-income areas had slower relative growth in heat-related activations (RRR, 0.86; P < .001 for areas with incomes of $100,000-$150,000 and RRR, 0.75; P = .03 for areas with incomes ≥ $200,000).

IN PRACTICE:

"Middle-aged adults (35-64 years) and the West South Central and Mountain census divisions showed heat-related EMS activations rising faster than non-heat-related EMS activations. These patterns may reflect occupational heat exposure, as middle-aged adults comprise the primary workforce and these regions concentrate outdoor industries with limited heat protections," the authors wrote.

SOURCE:

The study was led by Chris Chaeha Lim, PhD, Mel and Enid Zuckerman College of Public Health, University of Arizona, Tucson, Arizona. It was published online as a research letter on February 4, 2026, in JAMA.

LIMITATIONS: 

The study was limited by potential underreporting of heat‑related cases, reliance on clinician‑assigned diagnostic codes, and inability to track clinical outcomes after EMS transport, which limited the assessment of heat-related health effects and the long-term consequences of these effects.

DISCLOSURES:

The study was funded by the National Institute of Environmental Health Sciences, the National Institute on Minority Health and Health Disparities, and the US Department of Energy, Office of Science, Office of Biological and Environmental Research Urban Integrated Field Laboratories. Some authors reported receiving grants from various organizations; detailed are provided in the original article.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.