Seasonal association between ambient fine particulate matter and venous thromboembolism in Beijing, China: a time-series study

Little is known about the influence of ambient fine particulate matter (PM_2.5) on the incidence of venous thromboembolism in areas with heavy air pollution. We examined seasonal associations between airborne concentrations of fine particulate matter and outpatient visits for venous thromboembolism in Beijing using a city-wide time-series design that covered a period of 30 months (January 1, 2010 to June 30, 2012). Generalized additive models were used to investigate the associations with adjustment of temperature for various time lags (lag 0 for the warm season and lag 0–10 for the cold season). Overall, 92,435 outpatient visits were recorded by the Beijing Medical Claim Data for Employees database during the study period. We found a significant association between PM_2.5 levels and outpatient visits for venous thromboembolism. A 10-μg/m³ increase in PM_2.5 concentrations on lag days 0–2 corresponded to a 0.64% (95% confidence interval: 0.55–0.73%; P < 0.001) increase in outpatient visits for venous thromboembolism during the cold season, and a 10-μg/m³ increase in PM_2.5 concentrations on lag days 0–3 corresponded to a 0.82% (95% confidence interval: 0.67–0.96%; P < 0.001) increase in outpatient visits for venous thromboembolism during the warm season. Our findings suggest that PM_2.5 exposure is associated with outpatient visits for venous thromboembolism in Beijing, and a more pronounced association was observed during the warm season. We propose that various temperature-adjustment strategies should be used when investigating seasonal associations.