Particulate matter air pollution and COVID-19 risk: A systematic review

ABSTRACT

Introduction/Aim: Ecological studies indicate ambient particulate matter >=2.5 mm (PM 2.5) air pollution is associated with poorer COVID-19 outcomes. However, these studies cannot account for individual heterogeneity and often lack precision in estimates of PM 2.5 exposure. We summarise evidence relating on individual-level data to determine whether PM 2.5 exposure increases the risk of COVID-19 infection, severe disease and death. Method(s) We conducted a systematic review of relevant case-control and cohort studies, searching Medline, Embase and the WHO COVID-19 databases. Study quality was evaluated using the Newcastle-Ottawa Scale. Result(s) N = 18 studies met the inclusion criteria. Generally, PM 2.5 exposure was significantly associated with higher rates of COVID-19 infection (all 7 studies positive) and severe COVID-19 disease (8 of 9 studies positive, 1 null). The effects on mortality were mixed but indicative of a positive association (4 of 6 studies positive, 2 null). Most studies were rated 'good' quality (13 of 18 studies), though there were still methodological issues;few used individual-level data to adjust for important confounders like socioeconomic status (3 of 18 studies), instead using area-based indicators (12 of 18 studies) or not adjusting for it at all (3 of 18 studies). Most studies with severe disease (9 of 10 studies) and mortality outcomes (5 of 6 studies) were based on people already diagnosed COVID-19, potentially introducing collider bias. Conclusion(s) There is strong evidence that ambient particulate matter air pollution increases the risk of COVID-19 infection, and weaker evidence of increases in risk of severe disease and mortality.