Extreme Heat and Emergency Health Impacts in the US (2018-2025).

Future climate projections suggest an increase in heat-related mortality and a decrease in cold-related deaths under warming scenarios. Understanding the health impacts of extreme heat, and their implications for healthcare demand is essential for assessing the future burden of climate-related illnesses. In this study, we examined the relationship between extreme heat events and Emergency Department Visits (EDV) for heat-related illnesses (HRIs) across the United States from 2018 to 2025. Using data from the Centers for Disease Control and Prevention (CDC) Heat and Health Tracker and other relevant sources, we analyzed EDV rates standardized to 100,000 population. We aggregated daily into the 10 U.S. Health and Human Services (HHS) Regions. We used 0.5° × 0.5° gridded maximum daily temperature data (aggregated to HHS regions with proportional area weighting) and daily maximum heat index extracted from the CDC data portal (estimated using the US National Weather Service methodology and aggregated to HHS regions using total population weighting) to characterize seasonal patterns and regional variability. The association between peak heat events and EDV time series was explored using log-linear mixed-effects models, which accounted for seasonal trends, climate variables, and their regional variability. Random effects were used to capture regional heterogeneity in predictor-response relationships, accommodating variation in associations across regions. Model performance was evaluated using prediction error metrics and goodness-of-fit assessments. Maximum temperature and heat index were both significant predictors, with the heat index offering a slightly better fit. Associations were largely contemporaneous, with peak correlations at lag zero, underscoring the need for real-time response. EDV increased several days before peak environmental conditions, consistent with early exposure effects. While temperature-EDV relationships varied regionally, heat index associations were more stable. This work underscores the urgent need for regionally adaptive public health strategies in the face of intensifying climate extremes and outlines future directions for research and policy to strengthen health systems' preparedness in a warming world.