Short-term and long-term effects of air pollution on acute lower respiratory infections incidence and mortality: an overview and critical appraisal of systematic reviews

Background Acute lower respiratory infections (ALRIs) are a significant health concern, particularly affecting children and older adults. Air pollution is a known risk factor. Despite numerous systematic reviews exploring this relationship, varying methodological quality hinders the derivation of reliable concentration–response functions essential for health risk assessment. Methods We critically appraised systematic reviews investigating the association between air pollution and ALRI incidence and mortality, evaluating both short-term and long-term effects across age groups. Comprehensive searches were conducted in PubMed and Embase (up to November 2024). Included systematic reviews were evaluated using AMSTAR2-EH (A MeaSurement Tool to Assess systematic Reviews-Environmental Health), assessing methodological quality specific to environmental epidemiology. Results Among 330 unique systematic reviews, 15 met inclusion criteria. Short-term systematic reviews did not meet methodological appraisal standards. Studies on other pollutants, like ozone (O 3 ) and sulfur dioxide (SO 2 ), lacked conclusive methodologically high-quality evidence. Long-term systematic reviews generally demonstrated methodological rigour, linking nitrogen dioxide (NO 2 ) exposure to ALRI incidence in children (relative risk 1.09, 95% CI 1.03–1.16) and ALRI mortality in adults (relative risk 1.06, 95% CI 1.02–1.10 and 1.08, 95% CI 1.04–1.12 for NO 2 ; relative risk 1.204, 95% CI 1.095–1.325 for particulate matter with a 50% cut-off aerodynamic diameter of 2.5 µm (PM 2.5 )). Conclusions This overview systematically assessed systematic reviews using AMSTAR2-EH, highlighting methodological gaps, particularly in short-term studies, bias assessment and protocol registration. Overall, the evidence suggests a mild but significant association between short-term exposure to air pollutants and pneumonia incidence, and a stronger, more consistent association between long-term exposure and ALRI incidence and mortality, especially for NO 2 and PM 2.5 . These findings can inform public health policies and environmental regulations aimed at reducing respiratory disease burden due to air pollution.