(176) Incidence of Heat-Related Illness in the United States: A Retrospective Cohort Study Using the PharMetrics® Plus for Academics Dataset, 2017-2022

Background: The documented rise in the intensity, duration, and frequency of climate-induced heatwaves is linked to excess mortality and morbidity.

Objectives: To determine the incidence of heat-related illness (HRI) in the United States (US) from 2017-2022 and report the impact of COVID-19 on HRI incidence.

Methods: Retrospective cohort study using data from “PharMetrics® Plus for Academics”, a US administrative claims database, mapped to the Observational Medical Outcomes Partnership Common Data Model. We included individuals registered between 01 January 2017-31 March 2022, with a diagnosis for an acute event related to high temperature such as but not limited to exposure to excess sunlight, sunstroke, and heatstroke. Individuals could contribute to more than one event, with a wash out of 7 days. Annual and quarterly incidence rates [IR] (per 100,000 person-years) were computed and stratified by sex, age groups: < 18, 18-64 and ≥65 years, and US Census regions: Midwest, Northeast, South and West.

Results: We identified 141,675 individuals (50.3% women) who suffered a total of 285,555 HRI events. Mean age at first diagnosis was 63.7 years (SD: 15.9). The majority (38%) were from the West region. Individuals aged ≥65 years had the highest annual incidence of HRI (IR [95%CI]: men ranged from 2059[2029-2089] to 2,665.0[2,631.1-2,699.1]), women from 1148[1129-1168] to 1449[1427-1471]). IR in the other two age groups did not vary by sex. Across all regions, West individuals aged ≥65 had the highest IR (2127[2051-2206]-3528[3432-3625]). Lowest annual IR values were reported in 2020, during the COVID-19 pandemic. Observed seasonality of HRI was more pronounced in ≥65 age group: before the pandemic, HRI decreased during the January-March quarters and increased during April-June (e.g. 2346[2280-2414] vs 2692[2620-2765] respectively, for ≥65 years men in 2018). Lowest incidence in 2020 occurred in the April-June quarter (e.g., ≥65 age group: 1659[1606-1714] in men and 880[845-915] in women) whilst highest between July-September (e.g., ≥65 age group: 2418 [2353-2485] in men and 1359 [1316-1403] in women).

Conclusions: Men, individuals aged ≥65 and residents of the West regions of the US reported the highest incidence of HRI. A notable decrease in the IR was observed after the onset of the pandemic, which may be attributed to the public health restrictions during that period. Further study of these data on the incidence of heat-related illness can guide effective public health mitigation strategies aimed to reduce the impact of heat waves at both local and national levels in the US.