EVALUATING EXTREME HEAT-RELATED ILLNESS (HRI) AMONG SOCIO-VULNERABLE COMMUNITIES IN NORTH CAROLINA, USA: 2010-2020

Abstract

Extreme heat is a rapidly intensifying public health crisis that overwhelmingly burdens socio-vulnerable communities. Community-level social vulnerability is driven by factors such as socioeconomic position, minority status, household composition, and vehicle access, while individual-level vulnerability is heightened by disability, older age, and limited English proficiency. These intersecting conditions amplify risk during extreme heat events. Although daytime heat has been extensively characterized in national and state-level studies, the health impacts of persistently elevated nighttime temperatures in the United States remain underexplored.

This retrospective observational study rigorously evaluates the multifaceted impacts of extreme heat and heat-related illness (HRI), with a specific focus on nighttime temperatures, among vulnerable populations in North Carolina from 2010 to 2020. We integrated emergency department (ED) encounters, demographic records, meteorological data, and socioeconomic indicators. Logistic regression and descriptive analyses at the individual level quantified associations between HRI and nighttime temperature, geographic region, level of urbanization, gender, race, insurance status, and transportation access. Nighttime heat exposure was approximated using ED arrival times, and stratified random sampling ensured robust representation across North Carolina’s Mountain, Piedmont, and Coastal Plains regions.

We defined risk as the probability of experiencing HRI during periods of extreme heat, particularly under elevated nighttime temperatures, and operationalized it using odds ratios (ORs) and HRI rates per 1,000 ED visits across subpopulations and time periods. Later ED arrival times—indicating higher nighttime temperatures—were strongly and progressively associated with HRI. With every two-hour increment later into the evening, HRI odds increased by 6.7%. Marked geographic inequities emerged, with Piedmont and Coastal Plains residents experiencing substantially higher HRI risk than Mountain residents. Risk was also higher in suburban and rural counties than in urban counties. Male gender, public insurance coverage (Medicaid/Medicare), and ambulance transport independently elevated HRI risk, while Black residents had lower odds of HRI compared to White residents, diverging from some national patterns and underscoring the complexity of local risk profiles. These results demonstrate the complex influence of social determinants and environmental exposures on heat vulnerability.

Our findings establish persistent nighttime heat as a critical yet underrecognized driver of heat-related morbidity in North Carolina and reveal that socio-vulnerability to HRI is governed by a complex interplay of environmental, geographic, and social factors. This evidence demands targeted public health action, including tailored heat-warning systems, context-specific mitigation strategies, and equitable access to care, particularly for rural and socio-vulnerable communities. By filling a key knowledge gap on nighttime heat and HRI, this study delivers actionable insights to guide policy, preparedness, and future research aimed at advancing climate resilience and health equity.