“Our results add to the growing body of evidence that air pollution has a part to play in COVID-19 and support the potential benefit of improving air quality,” says Olena Gruzieva, associate professor at the Institute of Environmental Medicine at Karolinska Institutet and one of the study’s last authors.
The study draws on the population-based BAMSE project, which has regularly followed over 4,000 participants in Stockholm from birth. By linking these data to the national communicable disease registry (SmiNet), the researchers identified 425 individuals who had tested positive for SARS-CoV-2 (PCR test) between May 2020 and the end of March 2021. The average age of the participants was 26, and 54 per cent were women.
Traffic-related air pollutants
Daily outdoor concentrations of different air pollutants at the participants’ home addresses were estimated using dispersion models. The pollutants were particles with a diameter less than 10 micrometers (PM 10 ) and 2.5 micrometers (PM 2.5 ), black carbon and nitrogen oxides.
The researchers studied the associations between infection and exposure to air pollutants in the days before the positive PCR test, on the day of the test and on later control days. Each participant served as his or her own control on these different occasions.
The results show associations between infection risk and exposure to PM 10 and PM 2.5 two days before a positive test and exposure to black carbon one day before. They found no link between the risk of infection and nitrogen oxides.
The increase in risk was of an order of magnitude around seven per cent per particle exposure increase equivalent to the interquartile range, i.e. between the first quartile (25%) and the third quartile (75%) of the estimated particle concentrations.
Significance to public health