Association of short-term air pollution exposure with SARS-CoV-2 infection among young adults in Sweden

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Background and Aim Many ecological studies reported associations of short-term air pollution exposure with Corona-virus disease (COVID-19), however, no study examined this association on individual-level. We aimed to estimate the association between short-term exposure to ambient air pollution and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among Swedish young adults. Methods We conducted a time-stratified case-crossover study within the Swedish prospective birth cohort BAMSE (Swedish abbreviation for Children, Allergy Milieu, Stockholm, Epidemiology). We linked the cohort to Swedish national infectious disease registry to identify SARS-CoV-2 PCR-test positive cases between May 5, 2020 and March 31, 2021. Daily air pollutant levels (particulate matter ≤2.5 μm [PM2.5], particulate matter ≤10 μm [PM10], black carbon [BC] and nitrogen oxides [NOx]) were estimated at residential addresses using dispersion models with high spatiotemporal resolution. Distributed-lag models combined with conditional logistic regression models were used to estimate the association. Results A total of 425 cases were identified, of whom 229 (53.9%) were female and median age was 25.6 years. The median exposure level for PM2.5, PM10, BC and NOx was 4.4, 7.7, 0.3, 8.2 μg/m3 on case days and 3.8, 6.6, 0.2, 7.7 μg/m3 on control days, respectively. Each interquartile range (IQR) increase in short-term exposure to PM2.5 and PM10 on lag 2, BC on lag 1 was statistically significantly associated with a relative increase of 6.8% (95%CI: 2.1- 11.8), 6.9% (95%CI: 2.0 -12.1), and 5.8 % (95%CI: 0.3 – 11.6) of positive SARS-CoV-2 PCR test, respectively. There was no evidence of findings to be associated with NOx or modified by sex, smoking, asthma, overweight and self-reported COVID-19 respiratory symptoms. Conclusions Short-term exposure to PM and BC was associated with increased risk of testing PCR-positive for SARS-CoV-2 in young adults, supporting the broad public health benefits of reducing ambient air pollution levels.