Association between ambient air pollutants and influenza – A systematic review and meta-analysis

Abstract

• BACKGROUND AND AIM There is emerging evidence that ambient air pollution exposure is not linked solely to chronic diseases but might also impact incidence and mortality of infectious diseases. The aim of this systematic review and meta-analysis was to examine the association between exposure to ambient air pollutants and risk of influenza/influenza like illness (ILI) and associated infection, morbidity and mortality. • METHODS We conducted a systematic literature search and subsequently performed a random-effects meta-analysis using the Knapp-Hartung method with a restricted maximum likelihood (REML) estimator if at least four studies with similar outcome and exposure were available. We converted the estimates for each outcome into standardized increments for a 10 µg/m³ increase in air pollutant. Heterogeneity was assessed using I² and Cochranes Q. The study was registered at PROSPERO (CRD42020199906). An update including literature up to February 2022 is currently being prepared. • RESULTS The literature search from 01.01.1980 to 27.10.2020 yielded 233 studies from PubMed and Web of Science and one study from the preprint server MedRxiv. In total, 10 articles were reviewed in-depth and risk of bias assessed. For short-term studies, small positive associations were seen for a 10 µg/m³ increase in PM₂.₅ for influenza incidence [relative risk: 1.02, 95%confidence interval: 1.01; 1.03]. The search yielded only two studies for hospital admission and no long-term studies or studies on mortality. • CONCLUSIONS Our analysis indicates that ambient air pollution can exacerbate influenza infections. Lowering the current EU standards for PM₂.₅ will reduce the adverse effects of ambient air pollution for chronic as well as infectious diseases. The results for influenza might also give some implications of possible associations for ambient air pollution with other respiratory virus diseases including SARS-CoV-2. • KEYWORDS Influenza, influenza-like illness, meta-analysis, ambient air pollution, PM₂.₅