Association between air pollution-cold wave sequential events and ischaemic stroke incidence among elderly adults in Tianjin, China: a retrospective cohort study.

BACKGROUND: Both air pollution and temperature variability (with cold wave as an extreme form) may influence the incidence of ischaemic stroke (IS). This study aimed to examine the association between winter air pollution-cold wave sequential events (persistent air pollution followed by cold waves) and IS incidence among adults aged>=60 years. METHODS: Clinical data were sourced from the Tianjin Medical and Health Big Data Platform (covering 81 secondary/tertiary hospitals), and meteorological/air quality data were sourced from the National Meteorological Science Data Centre. Spearman rank correlation analysis was used to assess the relationships between meteorological variables (eg, 24-hour temperature decrease), atmospheric pollutants (including Air Quality Index (AQI)) and elderly IS incidence. A distributed lag nonlinear model (DLNM) was applied to analyse lagged effects of winter air pollution and cold wave sequential events on IS incidence, while a generalised additive model (GAM) was used to evaluate additive interactions between air pollution and cold waves on IS incidence. RESULTS: The study included 109 513 adults aged >=60 years with first-onset IS from 2016 to 2019. Eight winter air pollution-cold wave sequential events were identified over 4 years, with higher daily IS incidence during event periods (67 new cases/day), lag periods (68 new cases/day) than non-event periods (60 new cases/day). Subgroup analysis showed that among adults aged ≥80 years, proportional incidence during both events (80 to 85 years old: 1.89, 95% CI 0.52 to 3.26; 85 to 90 years old: 1.96, 95% CI 0.59 to 3.33) and lag period (80 to 85 years old: 0.90, 95% CI 0.02 to 1.78; 85 to 90 years old: 1.52, 95% CI 0.64 to 2.40) increased compared with the non-event period. Daily IS incidence was positively correlated with 24-hour temperature decreases, AQI and other air pollutants. DLNM showed that lag effects emerged 4 days post-exposure, with the highest IS risk at a 9-day lag (RR=1.122, 95% CI 0.443 to 2.838). GAM confirmed positive additive interactions between air pollution and cold waves on IS incidence (p<0.001). CONCLUSION: Winter air pollution-cold wave sequential events exert a synergistic, lagged effect on IS incidence in the elderly, with adults >=80 years being the most vulnerable. The observed risk patterns and underlying mechanisms underscore the importance of integrated environmental and public health strategies to reduce IS burden in this high-risk population.