Association between ambient temperature and the risk of hospital admission for injury in South Korea

Background: Extreme temperatures affect health, but nationwide evidence on injury-related hospitalization and economic burden in East Asia is scarce. We aimed to quantify the nonlinear and lagged associations between ambient temperature and injury-related hospitalization and the attributable economic burden. Methods: This nationwide time-stratified case-crossover study used the National Health Insurance Service-National Sample Cohort (2010-2019) of adults (≥20 years). The exposure was the district-specific percentile of daily mean temperature, and the outcome was inpatient hospital admission for injury. Conditional logistic regression with distributed lag nonlinear models (7-day lag, 3 degrees of freedom) was used to estimate relative risks (RRs) and 95% confidence intervals (CIs) at the 1st and 99th percentiles, each relative to the minimum injury temperature, adjusting for holidays, particulate matter concentrations (lag 0-1), and humidity. Analyses were stratified by age, sex, economic activity, residential area, and injury type. Societal economic burden was estimated using a human capital-based cost-of-illness approach. Results: -shaped relationship emerged. At the 1st percentile (cold), the RR was 1.151 (95% CI = 1.091, 1.214) with delayed effects (lags 1-6) primarily affecting limb injuries. Conversely, at the 99th percentile (heat), the RR was 1.157 (95% CI = 1.081, 1.239) with acute risks (lags 0-3) associated with severe injuries, such as multiple trauma (RR = 2.434, 95% CI = 0.886, 6.687) and burns (RR = 1.995, 95% CI = 1.272, 3.129). The total heat-related economic burden (24,649 million South Korean Won) exceeded that of cold (7,853 million South Korean Won). Individuals with low income, economically active groups, and provincial residents exhibited increased vulnerability to extreme heat, whereas females and the economically inactive population exhibited susceptibility to extreme cold. Conclusions: Nonoptimal temperatures increase injury risk and economic burdens while exacerbating inequalities. Integrating economic evaluations and targeted interventions into climate adaptation strategies is thus essential.