A systematic review and meta-analysis on the association between PM_2.5 exposure and increased influenza risk

Introduction: This systematic review and meta-analysis investigate the relationship between PM_2.5 exposure and increased influenza risk (e.g., increased hospital admissions, confirmed influenza cases), synthesizing previous findings related to pollutant effects and exposure durations. Methods: We searched PubMed, Web of Science, and Scopus for relevant studies up to 1 January 2010, following Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) guidelines for selection and analysis. Results: Our review included 16 studies and found that a 10 μg/m³ increase in daily PM_2.5 levels was associated with an increase of 1.5% rise in influenza risk (95% CI: 0.08%, 2.2%), with significant variations across different temperatures and lag times post-exposure. The analysis revealed heightened risks, with the most significant increases observed under extreme temperature conditions. Specifically, colder conditions were associated with a 14.2% increase in risk (RR = 14.2%, 95% CI: 3.5%, 24.9%), while warmer conditions showed the highest increase, with a 29.4% rise in risk (RR = 29.4%, 95% CI: 7.8%, 50.9%). Additionally, adults aged 18–64 were notably affected (RR = 4%, 95% CI: 2.9%, 5.1%). Discussion: These results highlight PM_2.5's potential to impair immune responses, increasing flu susceptibility. Despite clear evidence of PM_2.5's impact on flu risk, gaps remain concerning exposure timing and climate effects. Future research should broaden to diverse regions and populations to deepen understanding and inform public health strategies.