Study finds links between air pollution and severity of COVID

The researchers were able to show that more severe reactions to the virus were associated with higher long-term exposure to air pollutants. (Photo: Getty Images)

A comprehensive study of thousands of COVID-19 patients in Ontario hospitals finds links between the severity of their infections and the levels of air pollutants they are exposed to.

“This adds to the existing evidence that air pollution is a silent killer,” said Chen Chen, an environmental epidemiologist at the University of California and lead author of the study, published in the Canadian Medical Association Journal (AMC).

The study looked at more than 150,000 cases of COVID-19 in Ontario patients in 2020. It revealed how many of those patients were hospitalized with the disease, how many were transferred to intensive care units and how many lost their lives.

Researchers then turned to previously developed data that combined aerial surveillance records with other sources such as satellite imagery to model levels of three common pollutants across Ontario: particulate matter, nitrogen dioxide and tropospheric ozone.

Nitrogen dioxide is found in engine exhaust, which then breaks down into ozone in the atmosphere. Together, the three pollutants create smog.

The scientists then combined the health and pollution data with statistical methods to eliminate the impact of more than 10 different external factors such as pre-existing conditions and economic status.

The researchers were able to show that more severe reactions to the virus were associated with higher long-term exposure to air pollutants.

For every 25 percent increase in particulate matter a patient was exposed to, the likelihood of being hospitalized after contracting COVID-19 increased by 6 percent and the likelihood of being admitted to an intensive care unit increased by 9 percent.

The team found no link between fatality rates and particle exposure.

The effects were less for nitrogen dioxide. However, for ground-level ozone, the study found that the correlations were much higher for every 25% increase in exposure.

The probability of hospitalization increased by 15%. ICU admissions increased by 30% and the mortality rate was 18%.

“Among those already infected, we observed that some of those who had been exposed to higher levels of air pollution prior to being infected were more likely to have poorer outcomes,” Chen Chen said.

The study builds on previous research that looked at the direct links between pollution levels and COVID-19 infections. According to the epidemiologist, this approach does not capture what the long-term effects of air pollutants might be.

Chen Chen warns that the study doesn’t show that the three pollutants actually caused worsening of COVID-19 outcomes, but that wouldn’t come as a surprise. These pollutants are all known to irritate the lungs and lung function, and COVID-19 is a lung disease.

“We know that this virus attacks our pulmonary system. It is therefore possible that exposure to higher levels of air pollution prior to infection may make you more susceptible.

The epidemiologist says the study opens the door to more detailed investigations into how outcomes from COVID-19 vary: the effects of age or economic status, for example.

In addition, the study does not look for the mechanism by which air pollution might make the disease worse.

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