Association between short-term exposure to ambient air pollutants and the risk of hospital visits for acute upper respiratory tract infections among adults: a time-series study in Ningbo, China

Objectives: Acute upper respiratory tract infections (AURTIs) are prevalent in the general population. However, studies on the association of short-term exposure to air pollution with the risk of hospital visits for AURTIs in adults are limited. This study aimed to explore the short-term exposure to air pollutants among Chinese adults living in Ningbo. Methods: Quasi-Poisson time serious regressions with distributed lag non-linear models (DLNM) were applied to explore the association between ambient air pollution and AURTIs cases. Patients ≥ 18 years who visit three hospitals, being representative for urban, urban–rural junction and rural were included in this retrospective study. Results: In total, 104,441 cases with AURTIs were enrolled in hospital during 2015–2019. The main results showed that particulate matter with an aerodynamic diameter less than 2.5 μm (PM_2.5), nitrogen dioxide (NO₂) and nitrogen dioxide (SO₂), were positively associated to hospital visits for AURTIs, except for nitrogen dioxide (O₃), which was not statistically significant. The largest single-lag effect for PM_2.5 at lag 8 days (RR = 1.02, 95%CI: 1.08–1.40), for NO₂ at lag 13 days (RR = 1.03, 95%CI: 1.00–1.06) and for SO₂ at lag 5 days (RR = 1.27, 95%CI: 1.08–1.48), respectively. In the stratified analysis, females, and young adults (18–60 years) were more vulnerable to PM_2.5 and SO₂ and the effect was greater in rural areas and urban–rural junction. Conclusions: Exposure to ambient air pollution was significantly associated with hospital visits for AURTIs. This study provides epidemiological evidence for policymakers to control better air quality and establish an enhanced system of air pollution alerts.