Extreme Urban Heat and Emergency Department Visits in Older Adults.

Abstract

Health care systems can help protect patients from the increasing threat of extreme heat-driven morbidity and mortality. Electronic health records (EHRs) provide insight into trends and local variation in thresholds above which extreme heat is associated with emergency department (ED) use among at-risk patient populations. To examine associations between extreme heat exposure and all-cause ED visits among patients aged 65 years and older. This matched case-control study of patients seeking emergency care at an urban health care system during the summer (May 1 to September 30) from 2022 to 2024. Two New York City (NYC) EDs were included: (1) ED-1, predominantly serving Medicaid-enrolled patients from minoritized racial and ethnic groups, and (2) ED-2, predominantly serving White, privately insured patients. Included patients were aged 65 years or older and presented to ED-1 and ED-2 during the study period. Data were analyzed from April to August 2025. Daily maximum heat index (HImax) values during the summer were calculated from the National Centers for Environmental Information monitor-derived recordings. Daily all-cause ED use counts were derived from EHRs, and extreme heat exposure-outcome curves were calculated. Daily HImax anomalies were calculated based on a 30-year baseline average. The cumulative odds ratio (OR) and 95% CIs were calculated. This study included 55 200 ED encounters and represented 15 092 unique patients at ED-1 and 19 559 at ED-2 with a mean (SD) age of 74.9 (8.92) years at ED-1 and 74.9 (8.72) years at ED-2. Compared with ED-2, more ED-1 patients were female (8589 [56.9%] vs 10 767 [55.0%]), Hispanic (3544 [23.5%] vs 2576 [13.2%]), and Medicaid-enrolled (1321 [8.8%] vs 824 [4.2%]). At ED-1, daily HImax associations increased after 66 °F (OR, 1.10 [95% CI, 1.01-1.21]), peaking at 101 °F (OR, 1.24 [95% CI, 1.11-1.39]), and were higher on days with HImax anomalies between 15 °F (OR, 1.07 [95% CI, 1.01-1.13]) and 18 °F (OR, 1.10 [95% CI, 1.01-1.20]) warmer than average. At ED-2, daily HImax ED use associations were not significant and were significantly negative for days with HImax anomalies above 16 °F, nadiring at 21 °F (0.84, 95% CI [0.73, 0.95]) warmer than average. In this case-control study of the association between heat exposure and ED use in adults aged 65 years and older, positive associations were only observed at ED-1, which served a predominantly lower-income population from minoritized racial and ethnic groups. These association thresholds were not fully captured by NYC heat advisories, which were triggered by 2 days above HImax 95 °F or any time above 100 °F, highlighting an opportunity for future research to develop targeted, risk-informed health care system-based heat warning strategies.