Objective To understand the impact of air pollutant concentration on daily incidence of influenza, and provide scientific evidence for the prevention and control of influenza in Lanzhou, Gansu province.

Methods The daily incidence data of influenza and the data of air pollutant concentration in Lanzhou from January 1, 2023 to December 31, 2025 were collected for a Spearman correlation analysis. Distributed Lag Nonlinear Model (DLNM) was used to analyze the overall effect of each pollutant concentration on the daily incidence of influenza and the lag effects at different levels.

Results A total of 56 538 influenza cases were reported in Lanzhou from 2023 to 2025, in which 28 222 were men and 28 316 were women, the majority of the cases were 14 years and below (52.71%). Spearman correlation analysis indicated that the daily incidence of influenza was positively correlated with the concentrations of CO, NO₂, fine particulate matter (PM_2.5), inhalable particulate matter (PM₁₀), and SO₂ (r_s: 0.36, 0.37, 0.23, 0.14, and 0.11, respectively, all P<0.001), and negatively correlated with O₃ concentration (r_s: −0.48, P<0.001). Taking the median concentration of each pollutant as the reference, the overall effect of each pollutant on the daily incidence of influenza was nonlinear. Exposure to high concentration levels of CO, NO₂ and SO₂ showed the highest relative risks (RR) of 1.04 (95% CI: 1.01−1.07), 1.05 (95% CI: 1.03−1.08), and 1.03 (95% CI: 1.01−1.04) at lags of 3 days, 1 day, and 2 days, respectively. Exposure to low concentration levels of O₃ and PM10 had the highest RR of 1.11 (95% CI: 1.06−1.17) and 1.06 (95% CI: 1.03−1.10) at lags of 2 days and 12 days, respectively. The differences of lag effects of PM_2.5 at different levels were not significant.

Conclusion Exposure to high concentration levels of CO, NO₂ and SO₂, and low concentration levels of O₃ and PM₁₀ would increase the risk for influenza infection at certain lag times.