PM2.5 constituents and risk of influenza-like illness: A nationwide analysis in 289 Chinese cities

Discrepancies in fine particulate matter (PM_2.5)-related influenza‐like illness (ILI) risk have been widely observed in different studies in China, where the individual effect of PM_2.5 constituents might be one of the important reasons. However, the associations between PM_2.5 constituents and ILI risk in China have yet to be understood. We collected and aggregated weekly ILI cases in 289 Chinese cities during 2006-2019, and 47.8 million ILI cases were finally included in this study. Quasi-Poisson regression models and a random-effect meta-analysis were applied to estimate the impacts of PM_2.5 and its constituents on ILI risk. Stratification analyses were also conducted by region, age group, season, and temperature and humidity quartiles. With per inter-quartile range increase in black carbon, ammonium, sulfate, PM_2.5, nitrate and organic matter with a cumulative lag of 0-1 week, the overall ILI incidence would increase by 2.55% (95% CI: 1.71, 3.40), 2.32% (1.33, 3.32), 2.19% (1.29, 3.10), 2.19% (1.25, 3.13), 2.15% (1.08, 3.22) and 2.02% (1.19, 2.85), respectively. The impacts tended to be much stronger in young- and middle-aged population, in North and East China, in winter, and in colder and drier conditions. PM_2.5 and its major constituents all have significantly additive effects on ILI incidence. Specific preventive measures against individual constituent should be implemented for improving public health.