Selected Impacts of Urban Heat Islands on Emergency Medical Services Utilization in Rhode Island

Excessive environmental heat exposure is clearly associated with an increased likelihood that individual patients will suffer adverse health outcomes. Such heat exposure also strains healthcare systems via increased utilization, a burden which can challenge systems' capacities. Health impacts vary geographically with urban heat islands potentially contributing to higher temperatures and greater health risks. However, those most vulnerable to this exposure are not well identified. Our objective in this novel study was to compare and quantify differences in emergency medical services (EMS) use by selected patients during hot days in Rhode Island. Patients were recruited from low socioeconomic residential locations, stratified by whether they accessed EMS from within one of the state's "urban heat islands," or from other locations without "heat island" effects. We also compared selected patient demographic characteristics, and other EMS run data, between events associated with EMS access from these two types of areas.

This retrospective, cross-sectional cohort study evaluated how the probability of an EMS encounter varied in response to daily mean temperature and the urban heat island status of the encounter location. We aggregated EMS dispatch data, daily mean temperature, urban heat island classification and the Area Deprivation Index of the encounter location. A quasi-Poisson regression model assessed the relationship between EMS encounter frequency and potential risk factors including daily temperature, urban heat island status, year, day of the week, sex, age, and relevant interaction terms. The model was restricted to low socioeconomic, residential encounter locations to reduce confounding (noted elsewhere by year) and focus on the target population. The primary outcome was the rate ratio (RR) of EMS encounters for urban heat island locations vs locations without an urban heat island effect, in response to summer temperatures. Secondary outcomes included RRs of EMS encounters stratified by age, sex, weekday vs weekend, and year.

Higher temperatures were associated with increased EMS call rates across all demographic subgroups. A 5 °F (2.8 °C) increase in mean daily temperature was associated with an increase in an overall EMS encounter rate of 1.5% (RR, 1.015; 95% CI, 1.005-1.031, P = .004). On a weekday in 2021, at 75 °F degrees, 68 EMS encounters would be predicted for the residential, low socioeconomic status locations in the state while at 95 °F, 73 EMS encounters would be expected. The EMS rates were consistently higher in urban heat islands across all study years, after accounting for daily temperature, year, day of the week, demographic characteristics, population size and interactions between age, sex, urban heat island and weekday vs weekend. The largest relative increase in EMS encounters was observed in 2019, with rates 34% higher in urban heat islands compared to locations without an urban heat island effect (RR, 1.34; 95% CI, 1.27-1.42). The smallest increase occurred in 2020 (RR, 1.12; 95% CI, 1.06-1.18).

In residential and low socioeconomic locations, living in an urban heat island increased the probability of an EMS encounter, highlighting potential compounding effects of social and environmental vulnerability. As climate change intensifies extreme heat events, locationally targeted interventions may be critical in reducing heat-related health impacts.