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Previous studies have shown that areas of poor air quality have more cases of Covid-19, pointing to a potential link between the virus and rates of infection.
Now, researchers have found that exposure to certain traffic-related air pollutants can increase the risk of catching Covid by 7 per cent.
Scientists from the Karolinska Institutet examined the link between exposure to air pollutants at the home addresses of 4,000 young people in Stockholm and positive Covid tests among this cohort.
“Seven per cent doesn’t sound much, but given that everyone is more or less exposed to air pollutants, the association may be of great significance to public health,” said Erik Melén, a professor of paediatrics and one of the study’s joint authors.
The researchers merged a population-based project which has followed more than 4,000 participants in Stockholm from birth with Sweden’s national communicable disease registry, SmiNet.
They identified 425 people who had tested positive for Sars-CoV-2 between May 2020 and the end of March 2021. The average age of the participants was 26, and 54 per cent were women.
The researchers then studied the associations between infection and exposure to air pollutants on the days before the participants’ positive 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.
Daily outdoor concentrations of different air pollutants at the participants’ home addresses, including black carbon and nitrogen oxides, were estimated using dispersion models.
The study, published in Jama Network Open, found that exposure to black carbon and pollutant particles with a diameter less than 10 micrometres and 2.5 micrometres is associated with an increased risk of testing positive for Covid-19. There was no link between the risk of infection and exposure to nitrogen oxides.
Olena Gruzieva, an associate professor at the Institute of Environmental Medicine at Karolinska Institutet, said: “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.”
The researchers said the project was not prejudiced by gender, smoking, being overweight or asthma.
They noted that the results might be affected by the willingness to take a PCR test and the fact that many of the young adults were asymptomatic or had only mild symptoms following infection.
The researchers are now investigating the relationship between air pollutants and post-Covid symptoms in young adults.