Investigating links between air pollution, COVID-19 and lower respiratory infectious diseases – A review

Background/aim Hundreds of air pollution and COVID-19 papers have been published in a short time varying widely in quality. The Greater London Authority commissioned a comprehensive overview of the most credible evidence for the links between air pollution and COVID-19 and other lung infections. Methods Building on the Brunekreef et al (2021) review, a literature search was performed from November 2020 – May 2021, classifying the evidence by exposure, the potential mechanism and the health outcome. Studies on hospital admissions for lower respiratory infections were reviewed from 2011 Results Long-term exposure increased the risk of hospitalization in people already infected with COVID-19 in two good-quality cohort studies with individual data, perhaps due to respiratory and cardiovascular disease from air pollution increasing vulnerability to COVID-19 adverse outcomes. Mortality results were conflicting. Inconsistent results were found for long-term exposure and COVID-19 cases in ecological studies. Studies on short-term exposure were unclear and hard to evaluate. Several studies demonstrated that inhaled pollutant increased expression of the ACE2 receptor and other host susceptibility genes in both alveolar epithelial cells and macrophages. Susceptibility to infection by SARS-CoV-2 can be inferred from these results but only one study used SARS-CoV-2 directly. Several studies from 2011-2021 showed a link between air pollution and hospital admissions for lung infections although the studies were spread across different age groups and disease definitions. Particulate matter does not appear to play any important part in transporting COVID-19 in the environment, as had been suggested by some earlier studies. Conclusions The publication of cohort studies with individual data in this time period is an important step forward. Results are suggestive for long-term exposure and hospital admissions for COVID-19 and some toxicological effects are plausible but further research will be necessary to strengthen these emerging findings. Keywords Air pollution, COVID-19, lower respiratory infections.