Association between short-term exposure to fine particle air pollution and COVID-19

<bold>Background:</bold> Air pollution levels have been associated with the risk of contracting COVID-19, possibly due to particles acting as carriers of the virus, increasing infectivity, and exacerbating illness severity. This study aims to examine PM2.5 fluctuations and COVID-19 incidence in Sweden. <bold>Methods:</bold> We constructed a general population study cohort (REGAL) comprising Swedish participants from the Respiratory Health in Northern Europe (RHINE) study and the Global Allergy and Asthma European Network (GA2LEN) study, recruited from four cities (Stockholm, Gothenburg, Uppsala, and Umeå). Their data was linked with several national registers, including the Patient Register, Cause of Death Register, and Prescribed Drug Register. Daily PM2.5 levels and meteorological observations (temperature and relative humidity) for each city were obtained from national databases. Using a time-stratified case-crossover study design, we analyzed 3,811 cases (date of positive PCR test for SARS-CoV-2) between March 11, 2020, and Jan 26, 2022. Conditional logistic regression with a distributed lag non-linear model (DLNM) was used to evaluate potential delayed effects (0-14 lag days) between ambient air conditions and the increased risk of COVID-19. <bold>Results:</bold> The most pronounced associations between PM2.5 and COVID-19 were observed at lag 0 (same day). An interquartile range increase in PM2.5 (3.5 μg/m3) was associated with an odds ratio of 1.07 (95% CI: 1.01–1.13) at lag 0. Similarly, for individuals with respiratory diseases (asthma, COPD, n=377) an odds ratio of 1.20 (95% CI: 0.99–1.46) was estimated. <bold>Discussion:</bold> Higher levels of air pollution might exacerbate symptoms and, consequently, encourage testing.