Mortality Risk from Chronic Ischemic Heart Disease Associated with Short-Term Co-Exposure to Summer Heatwave and Ozone.

Summer heat and air pollution may pose a great threat to public health in the context of climate warming, however, their interactive effects on deaths from chronic ischemic heart disease (CIHD) have not been evaluated in existing investigations. This study aims to assess the associations of concurrent heatwave and ozone pollution with CIHD mortality in Chinese population. We carried out a province-wide, individual-level case-crossover study by analyzing 33,770 CIHD deaths occurring in warm season (May-September) across Jiangsu, eastern China, between 2016 and 2019. Spatially resolved estimates of maximum 8-h average ozone concentrations and air temperatures were estimated on case days and control days at the residential address. Heatwave events were defined using multiple temperature thresholds (percentiles 90-97.5) and durations (2-4 days). Conditional logistic regression model was employed to assess the odds ratio (OR) and its 95% confidence interval (CI) of CIHD death associated with heatwave and ozone exposure. Stratified analyses were performed to compare ozone-related risks on heatwave days versus non-heatwave days, and heatwave-related risks on low-ozone days versus high-ozone days. Additive interactive effects were testified using multiple metrics including relative excess odds due to interaction (REOI), proportion attributable to interaction (AP), and synergy index (SI). In the overall population, the odds of CIHD mortality were 1.010 (95% CI, 1.007-1.014) for a 10-µg/m