An observational JAMA Network Open study today involving young adults in Sweden suggests that short-term exposure to even relatively low levels of air pollution is tied to a higher risk of later testing positive for COVID-19, likely by worsening symptoms in those already infected.

A team led by researchers from the Karolinska Institutet in Stockholm linked the prospective Children, Allergy Milieu, Stockholm, Epidemiology birth cohort (following 4,089 infants born from 1994 to 1996) to the Swedish national infectious disease registry to identify positive COVID-19 test results from May 5, 2020, to Mar 31, 2021.

From August to June 2021, participants were invited to complete online questionnaires and undergo a clinical examination. Median age was 25.6 years.

A total of 425 participants were diagnosed as having COVID-19. The investigators used dispersion models to estimate daily levels of air pollution consisting of particulate matter, black carbon, and nitrogen oxides at home addresses. The primary source of air pollution in Stockholm is road traffic, the researchers noted.