Long-Term Exposure to Particulate Matter 2.5 and Ozone and the Risk of Acute Respiratory Infections: Community-Based Prospective Cohort Study.

BACKGROUND

Acute respiratory infections (ARIs) remain a major global health concern. Although long-term air pollution exposure has been linked to ARIs, prospective evidence from community-based populations remains limited.

OBJECTIVE

This study aimed to quantify the burden of ARIs in the community and examine the associations between long-term exposure to particulate matter 2.5 (PM2.5) and ozone (O3) and the risks of ARIs, with additional analyses using influenza-like illness (ILI) as a more specific outcome.

METHODS

We conducted a prospective cohort study including 3617 residents in Shanghai, China, who were followed weekly for 1 year. Individual-level exposure to PM2.5 and O3 concentrations was estimated using high-resolution datasets. Cox proportional hazards models with shared frailty were applied to assess associations with ARIs. Exposure windows of 3, 6, 9, and 12 months were evaluated, and the optimal window was selected based on the Akaike information criterion. Effect estimates were reported per IQR increase. Dose-response relationships, subgroup analyses, and multiple sensitivity analyses were performed.

RESULTS

During 3217 person-years of follow-up, 885 ARI events were documented (0.27 per person-year). In the fully adjusted model using the 12-month exposure window, each IQR increase in PM2.5 was associated with higher risks of ARIs (hazard ratio [HR] 1.594, 95% CI 1.340-1.897), with stronger associations observed for ILI (HR 1.948, 95% CI 1.484-2.557). For O3, the corresponding HRs were 1.510 (95% CI 1.135-2.007) for ARIs, with stronger associations for ILI (HR 2.229, 95% CI 1.385-3.588). PM2.5 showed a nonlinear association with ARIs, whereas linear relationships were observed for PM2.5 with ILI and O3 with both outcomes. Evidence of effect modification was observed by age, residence, and season for PM2.5 and by season for O3. Results were robust across multiple sensitivity analyses.

CONCLUSIONS

Long-term exposure to PM2.5 and O3 is associated with increased risk of ARIs, with similar associations observed for ILI. These findings highlight the importance of long-term air pollution control and targeted interventions for susceptible populations, particularly during cold seasons.