Rising Temperatures, Rising Calls: Environmental Heat's Burden on EMS in Boston at the City and Neighborhood Scales

Heat exposure can exacerbate cardiovascular, respiratory, and chronic diseases and affect health system operations. Existing research has identified increased citywide emergency medical services (EMS) call volume associated with hot and humid days, but how the phenomenon varies by neighborhood is less well understood. In this work, the relationship was analyzed for the warm seasons of 2016-2022 in Boston with relative risk and time series analyses at the city and neighborhood levels. At the city level, hot and humid days had a relative risk of 1.06 (95% confidence interval (CI) = 1.04, 1.07). For each 10 °F heat index increase from 60 °F, 80 °F, and 100 °F, the expected EMS incident volume increased by 3.1%, 1.9%, and 1.4%, respectively (3.1%, 1.0%, and 0.9% when air pollutants were adjusted for). At the neighborhood level, vegetation greenness and social vulnerability were significant covariates. Neighborhoods exhibited different sensitivities to heat exposure even after adjusting for these variables. A complex response relationship was observed in one neighborhood where the expected EMS incident volume grew as heat index increased until about 80 °F, tapered off slightly, before growing nearly exponentially again once heat index exceeded 100 °F. In contrast, another neighborhood had a nearly flat response relationship. The relationships in other neighborhoods were situated between these extremes. Increasing vegetation coverage, reducing socioeconomic disparities, and mitigating their effects may reduce EMS incident volume. Tailoring EMS resources to neighborhood heat sensitivities, increasing staffing and spare equipment during hot weather may improve system performance.