Modification by seasonal influenza and season on the association between ambient air pollution and child respiratory diseases in Shenzhen, China

Objective: To quantify the acute effect of ambient air pollution on the risk of respiratory diseases in children in a Chinese subtropical city, and to investigate whether seasonal influenza and season could modify this association. Methods: A Generalized Additive Model was performed to evaluate the association between ambient air pollutants, including fine particulate matter (PM2.5), respirable particulate matter (PM10), ozone (O-3), sulfur dioxide (SO2), and nitrogen dioxide (NO2), and children's hospital visits for respiratory diseases in Shenzhen, China. Potential effect modification was identified by stratified analysis in terms of seasonal influenza and seasons. The robustness of the results was assessed by sensitivity analyses. Results: A total of 2,569,021 hospital visits for respiratory diseases were recorded among children under 15 years old. We observed significant acute effects of air pollution, and the largest effects were observed during lag2 (two days after exposure) for PM2.5 [excess risk (ER) = 2.50% (95% CI: 1.88%, 3.12%)], PM10 [ER = 1.79% (95% CI: 1.37%, 2.21%)], O-3 [ER = 0.59% (95% CI: 0.23%, 0.95%)], and SO2 [ER = 7.84% (95% CI: 5.17%, 10.58%)], and during lag0 (day of exposure) for NO2 [ER = 2.39% (95% CI: 1.74%, 3.05%)]. Season modified these effects with stronger associations being observed during the cold season. Seasonal influenza modified the effects of particulate matters towards stronger association during seasonal influenza epidemic, but this modification was not statistically significant. Conclusion: Ambient air pollutants, specifically PM2.5, PM10, O-3, SO2, and NO2, were significantly associated with increased child hospital visits for respiratory diseases in Shenzhen, China. The vulnerable windows for these effects were the cold season and seasonal influenza epidemics.