Inequities in heat-related emergency department visits in California from 2005 – 2017

Rising temperatures and extreme heat pose a substantial threat to human health through increases in heat-related morbidity and mortality. Moreover, social determinants of health can exacerbate the impact of heat on susceptible populations. This study investigates the inequities in heat-related emergency department (ED) visits in California from 2005-2017, focusing on how social determinants of health, represented by the California Healthy Places Index (HPI), may influence the associations between temperature and ED visits. A Distributed Lag Nonlinear Model (DLNM) was employed to assess the association between daily temperatures and ED visits for heat-related physical illness, mental health, and all-cause visits. The California HPI was used to stratify the data and evaluate disparities in heat-related ED visits across different socioeconomic conditions. There were 129,935,301 ED visits in California from 2005-2017. We find that 5.1% of heat-related physical illness visits, 5.4% of heat-related mental health visits, and <1% of all-cause ED visits in California were attributable to heat. Communities with lower HPI scores (indicating less healthy conditions) accounted for a higher proportion of ED visits than expected based on their population size, and higher burdens of heat-related morbidity, with four times greater risk of heat-attributable ED visits for physical illness, and two times greater risk for mental health and all-cause visits. This study underscores the disproportionate impact of extreme heat on communities with less healthy conditions and highlights the importance of social determinants of health in shaping heat-related morbidity. Heat-attributable emergency department visits represent a sizable portion of overall morbidity for heat-related outcomes and mental outcomes. Communities with the least healthy conditions have disproportionately higher heat-related morbidity.