Thus, air pollution can be considered a factor, even indirect, of the risk of infection with COVID-19. In particular, the average annual increase of 1 µg / m3 linked to a 5% increase in the infection rate is thus associated with 294 additional cases / 100,000 people per year.
The association of pollution and viral infections
The study is being carried out in a city in northern Italy, a region hard hit by the pandemic both in terms of cases and deaths. Many reasons have been cited for these high incidence rates, including demographics and local strategies implemented. A broader look at the European region, however, reveals that a large part of the 3.9 million Europeans residing in areas where air pollution exceeds European limits live in northern Italy.
Pollution and COVID-19: it has been suggested by previous studies cited by the researchers that air pollution is a risk factor for COVID-19 infection, however, until then, there was insufficient data to conclude. This new study therefore looked at long-term exposure to air pollutants and COVID-19 infection patterns from the start of the pandemic to March 2021 among residents of Varese, the eighth largest city in Lombardy. The researchers were able to assign 97% of the 81,543 residents to 2018 average annual exposure levels for key air pollutants, based on home address. Regional data on COVID-19 infection, hospitalizations and outpatient drug prescriptions were collected for 62,848 adults not yet infected with SARS-CoV-2. Only 3.5% of the population of the whole region were fully vaccinated by the end of March 2021. Finally, the estimates of the annual and seasonal average levels of 5 air pollutants (particulate matter (PM2.5, PM10); nitrogen dioxide (NO2); nitric oxide (NO); ozone (O3))
- 4,408 new cases of COVID-19 were recorded between February 25, 2020 and March 13, 2021 – a rate of 6,005 cases / 100,000 inhabitants / year;
- population density does not appear to be associated with an increased risk of infection;
- living in a retirement home is associated with a risk of infection more than 10 times higher;
- undergoing drug treatment for diabetes, high blood pressure or obstructive airway disease (COPD), having a history of cerebrovascular accident (stroke) are respectively associated with an increased risk of 17%, 12% , 17% and 29% of COVID-19;
- after taking into account age, sex, possible residence in nursing homes and co-morbidities, exposure to PM2.5 and PM10 particles is found to be significantly associated with an increase in the rate of COVID-19;
- each 1 µg / m3 increase in long-term exposure to PM2.5 is associated with a 5% increase in the number of new cases of COVID-19 infection;
- taking into account seasonal rather than annual exposure averages gives similar results;
- similar associations are observed for PM10, NO2 and NO.
the associations observed are even more marked among the older age groups,
indicating a stronger effect of pollutants on the rate of COVID-19 infection in 55-64 and 65-74 year olds.
“A path” between exposure to pollution and the impact of COVID-19: this is an observational study which therefore does not demonstrate a cause and effect relationship. Pollution could indeed be associated with other direct factors of infection, including mobility, social interactions, humidity, temperature and certain diseases. Long-term exposure to air pollution indeed increases the risk of respiratory and cardiovascular disease due to persistent inflammation and compromises immunity. These same pathways could therefore be involved in the link between air pollution and COVID-19 infection rates.
However, the study does reveal a “path” between long-term exposure to air pollution and the impact of COVID-19, with implications for the most vulnerable. Finally, reducing the incidence of viral infections also requires efforts to reduce air pollution, the researchers conclude.