Environmental pollution increases the risk of COVID-19 infection

Exposure to air pollutants is linked to an elevated risk of SARS-CoV-2 infection, as demonstrated by an observational study of young adults in Stockholm, Sweden. The document was produced by researchers at the Karolinska Institutet and published on JAMA Network Open.

Scientists sought to elucidate whether air pollution could increase the risk of infection, as well as the severity of the COVID-19 disease. This question is based on the fact that pollution has long been recognized as a potential contributor to infectious respiratory diseases such as influenza, severe acute respiratory syndrome, and dengue.

Researchers have summarized two key pathways for the plausible link between air pollution and COVID-19 outcomes: modifying the host's susceptibility to infection or the severity of the disease and raising the risk of comorbidities. The first pathway may be mediated by up-regulation of proteins critical for viral entry and by suppression of the immune system due to oxidative stress, epithelial damage, and lung inflammation.

Within this framework, and given that outdoor air pollutants can increase the risk of respiratory infections, including COVID-19, researchers at the Karolinska Institutet Institute of Environmental Medicine in Stockholm, Sweden, have set out to study the link between estimated exposure to household air pollutants and positive PCR tests for SARS-CoV-2 in young adults in Stockholm.

The results they arrived at show that exposure to certain traffic-related air pollutants is associated with a greater likelihood of testing positive for COVID-19.

“Our results add to the growing body of evidence that air pollution has a role to play in the COVID-19 pandemic and support the potential benefit of improving air quality,” said Olena Gruzieva, associate professor at the Institute of Environmental Medicine at the Karolinska Institutet and one of the authors of the document.

The study was based on the BAMSE project, Swedish abbreviation for children, allergy, environment, Stockholm, epidemiology, is a prospective, longitudinal and ongoing population-based birth cohort, which includes 4089 children born between 1994 and 1996 in Stockholm, Sweden.

The scientists, by linking these data to the National Registry of Communicable Diseases (SMInet), identified 425 people who tested positive for SARS-CoV-2 (by PCR test) between May 2020 and the end of March 2021. The average age of the participants was 26 years old, and 54 percent of them were women.

Daily outdoor concentrations of different pollutants in the addresses corresponding to the participants' homes were estimated using dispersion models. The contaminants studied were particles with a diameter of less than 10 micrometers (PM10) and 2.5 micrometers (PM2.5), black carbon and nitrogen oxides.

The researchers studied the associations between infection and exposure to contaminants in the days before the positive PCR test, the day of the test, and on the subsequent control days. Each participant served as their own control on these different occasions. The results obtained showed associations between the risk of infection and exposure to PM10 and PM2.5 two days before a positive test and exposure to black carbon one day earlier.

They found no link between the risk of infection and nitrogen oxides. The observed association was not influenced by sex, smoking, overweight or asthma.

The increase in risk was an order of magnitude of about 7% due to the increase in particulate matter exposure between the first quarter (25%) and the third (75%) of the estimated particulate concentrations.

“7% doesn't seem like much, but given that everyone is more or less exposed to air pollutants, the partnership can be of great importance to public health,” admits Erik Melén, professor of pediatrics in the Department of Clinical Sciences and Education and leader of the BAMSE project, as well as author of the study.

Researchers point out that the results could be affected by willingness to perform a PCR test and the fact that many of the young adults were asymptomatic or had only mild symptoms after infection. Nor can the study rule out the possibility that time-varying confounding factors have also influenced the results.

Specialists are now making progress in the analysis between the link between air pollutants and post-COVID-19 symptoms in young adults.

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