The association between ambient pollutants and influenza transmissibility: A nationwide study involving 30 provinces in China

BACKGROUND: The impact of exposure to ambient pollutants on influenza transmissibility is poorly understood. We aim to examine the associations of six ambient pollutants with influenza transmissibility in China and assess the effect of the depletion of susceptibles. METHODS: Provincial‐level surveillance data on weekly influenza‐like illness (ILI) incidence and viral activity were utilized to estimate the instantaneous reproduction number (R(t)) using spline functions. Log‐linear regression and the distributed lag non‐linear model (DLNM) were employed to investigate the effects of ambient pollutants—ozone (O(3)), particulate matter ≤2.5 μm (PM(2.5)), particulate matter ≤10 μm (PM(10)), nitrogen dioxide (NO(2)), sulfur dioxide (SO(2)), and carbon monoxide (CO)—on influenza transmissibility across 30 Chinese provinces from 2014 to 2019. Additionally, the potential effects of the depletion of susceptibles and regional characteristics were explored. RESULTS: There is a significantly positive correlation between influenza transmissibility and five distinct ambient pollutants: PM(2.5), PM(10), SO(2), CO, and NO(2). On average, these ambient pollutants explained percentages of the variance in R(t): 0.8%, 0.8%, 1.9%, 1.3%, and 1.4%, respectively. Conversely, O(3) was found to be negatively associated with R(t), explaining 1.5% of the variance in R(t). When controlling for the effect of susceptibles depletion, the effects of all pollutants were more pronounced. The effects of PM(2.5), PM(10), CO, and SO(2) were higher in the eastern and southern regions. CONCLUSIONS: Most ambient pollutants may potentially contribute to the facilitation of human‐to‐human influenza virus transmission in China. This observed association was maintained even after adjusting for variation in the susceptible population.