Extreme heat and air pollution can trigger a wide range of acute health events, yet multiple co-occurring exposures have rarely been evaluated within a unified analytical framework. We examined short-term associations between heat index (HI), major air pollutants (nitrogen dioxide: NO2, ozone: O3, black carbon: BC, and non-black carbon: NBC), and ten categories of acute health events using individual-level hospitalization and emergency department data from Wisconsin during warm seasons (May-September, 2018-2023). We applied a disjoint time-stratified case-crossover design with conditional Poisson regression and distributed lag non-linear models to estimate exposure-specific conditional effects. HI was significantly associated with multiple outcomes, with respiratory risk increasing by approximately 30% at high heat levels (RR ≈ 1.3). Heat-related events showed stronger responses, with risks exceeding tenfold at extreme HI levels (RR > 10). NO2 exhibited the most consistent associations, including an 18% increase in mental health events (RR ≈ 1.18) and up to 50% higher risk for alcohol-related events (RR ≈ 1.5) at higher concentrations. O3 showed limited associations, whereas BC and NBC demonstrated threshold-dependent effects with plateauing risks. These findings highlight heterogeneous, lag-dependent health impacts of extreme heat and air pollution and underscore the importance of multi-exposure assessment for acute risk evaluation.
Choi et al. (Sun,) studied this question.