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 face.
“This adds to 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 admitted to hospital with the disease, how many were transferred to intensive care units and how many lost their lives. The researchers then turned to previously developed data that combined air monitoring records with other sources, such as satellite imagery, to model the levels of three common pollutants across Ontario: fine particulate matter, nitrogen dioxide, and tropospheric ozone.
Nitrogen dioxide is contained in the exhaust gases emitted by engines and then breaks down in the atmosphere into ozone. Together, the three pollutants create smog. The scientists then combined the health and pollution data, using statistical methods to remove the effects 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 levels of long-term exposure to airborne contaminants. For every 25% increase in fine particulate matter a patient was exposed to, the odds of being admitted to the hospital after becoming infected with COVID-19 increased by 6% and the odds of being admitted to an intensive care unit increased by 9%.
The team found no link between death rates and particulate exposure. The effects were smaller for nitrogen dioxide. However, for tropospheric ozone, the study found that the correlations for every 25% increase in exposure were much higher. The chances of hospital admission increased by 15%. ICU admissions increased 30% and mortality rates were 18%. “Among those who were already infected, we observed that some of those who were exposed to higher levels of air pollution before infection had a higher chance of worse outcomes,” according to Chen Chen. The study builds on previous research that has looked at immediate 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 could be.
Chen Chen cautions that the study doesn’t establish that the three contaminants actually worsened COVID-19 outcomes, but that wouldn’t be a surprise. All of these pollutants are known to irritate the lungs and lung function, and COVID-19 is a lung disease. “We know that this virus attacks our pulmonary system. So it’s possible that being exposed to more air pollution before infection makes you more vulnerable. The epidemiologist says the study opens the door to more detailed research on how COVID-19 outcomes vary: for example, on the impact of age or economic status. In addition, the study does not look at the mechanism by which air pollution could worsen the disease.
Photo credit: Archive.
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