Exposure‐Response Associations Between Air Pollution and Laboratory‐Confirmed Influenza Cases in Anhui Province, China: A Two‐Stage Modeling Study

Influenza remains a global public health and socio‐economic threat, and air pollution is believed to increase its risk. However, relatively few studies have focused specifically on laboratory‐confirmed influenza (LCI), which limits the precision and reliability of existing evidence on this association. We sought to explore the relationship between air pollution and LCI cases in Anhui province, China. We employed a two‐stage time series analysis to evaluate the associations between PM 2.5 , PM 10, CO, SO 2 , O 3 , NO 2 and daily LCI cases between January 2015 and March 2023. In the first stage, we applied distributed lag nonlinear model to characterize the lagged effects of each air pollutant in individual cities, followed by a meta‐analysis to pool city‐specific estimates in the second‐stage. We performed sub‐group analysis by age and gender, and explored modification effect of population density, median pollution levels, longitude, and latitude, using a meta‐regression. A total of 43, 872 LCI cases were reported in Anhui over study period. There was a positive associations between influenza and a 10 μg/m 3 increase in PM 2.5 : RR = 1.0045 (95%CI: 1.0035–1.0054), SO 2 : RR = 1.0035 (95%CI: 1.0001–1.0069), NO 2 : RR = 1.0122 (95%CI: 1.0881–1.0162), PM 10 : RR = 1.0025 (95%CI: 1.0017–1.0033) and CO: RR = 1.2641 (95%CI: 1.1294–1.4150) in a single‐day lag model. In the cumulative‐day lag model, a 10 μg/m 3 increase in PM 2.5 ; RR = 1.0043 (95%CI: 1.0018–1.0068), NO 2 ; RR = 1.0076 (95%CI: 1.0006–1.0145), PM 10 ; RR = 1.0024 (95%CI: 1.0001–1.0046), and CO; RR = 1.3026 (95%CI: 0.8139–2.0849) positively associated with LCI cases. The associations were more pronounced in males and ages 5–24 years. Population density modified the associations. Our findings suggest the need to integrate air quality management in intervention strategies for influenza.