Air pollution exposure linked to more severe COVID-19 outcomes

Exposure to common air pollutants were associated with more severe outcomes after SARS-CoV-2 infection, according to findings published in the Canadian Medical Association Journal.

“Apart from showing that the environment, and especially air pollution, may play a role in contributing to COVID-19 severity during the COVID-19 pandemic, this study enforces the idea that air pollution is pervasive and a silent killer,” Hong Chen, PhD, an adjunct professor in the School of Epidemiology and Public Health at the University of Ottawa in Canada, told Healio. “The association of air pollution and COVID-19 severity reflects the tip of the iceberg of the wide-ranging impacts of air pollution on human health.”

In a population-based cohort study, Chen and colleagues evaluated the association between long-term exposure to fine particulate matter (PM_2.5), nitrogen dioxide (NO₂) and ground-level ozone (O₃) among 151,105 adults aged 20 years or older with a confirmed SARS-CoV-2 infection living in Ontario, Canada. They concentrated on key indications of COVID-19 severity like hospital admission, ICU admission and death, and followed patients from 2020 until the occurrence of COVID-19 outcomes, or May 2021. Long-term exposure to air pollution was estimated based on participants’ residences from 2015 to 2019.

Among the study cohort, 5.7% of participants had COVID-19-related hospital admissions, 1.3% had ICU admissions and 1.4% died. This amounted to 8,630 hospitalizations, 1,912 ICU admissions and 2,137 deaths related to COVID-19, according to the researchers. The median time between first diagnosis and these outcomes was 5 days, 8 days and 15 days, respectively.

Chen and colleagues reported that the median interquartile ranges (IQRs) of long-term exposure to air pollutants were 7.64 µg/m3 (95% CI, 6.43-8.13) for PM_2.5, 7.75 ppb (95% CI, 6.15-8.65) for NO₂ and 44.8 ppb (95% CI, 42.41-47.38) for O₃.

For each IQR increase in exposure to PM_2.5 of 1.7 µg/m3, the researchers estimated odds ratios of 1.06 (95% CI, 1.01-1.12) for hospital admissions, 1.09 (95% CI, 0.98-1.21) for ICU admissions and one (95% CI, 0.9-1.11) for death. The estimated odds ratios were smaller for NO₂, with an odds ratio of 1.09 (95% CI, 0.97-1.21) per IQR increase of 2.5 ppb NO₂ for ICU admission, Chen and colleagues reported. However, there was no observed effect for hospital admissions or death with NO₂.

The odds ratios for O₃ per IQR increase of 5.14 ppb was 1.15 for hospital admissions (95% CI, 1.06-1.23), 1.3 for ICU admissions (95% CI, 1.12-1.5) and 1.18 for deaths (95% CI, 1.02-1.36).

Overall, the findings indicate that long-term exposure to PM_2.5 and O₃ was associated with an elevated risk for COVID-19–related hospital admissions; exposure to O₃ was also associated with an elevated risk for death due to COVID-19. Additional research is needed to better understand how long-term air pollution may affect COVID-19 severity, according to the researchers.

Globally, air pollution is the largest environmental risk factor for disease and is responsible for millions of premature mortalities, Chen said.

"Climate change has profound impacts on human health, ranging from triggering extreme heat and other severe weathers, to increasing the spread of so called ‘climate-sensitive’ diseases, like Lyme disease and enterovirus infections, and heightening the frequency of wildfires,” Chen said. “It can affect health by worsening socioeconomic conditions ... disrupting health services and magnifying preexisting health inequities. All of these will affect our response and care to infectious diseases.”

References:

Air pollution associated with more severe COVID-19. https://www.eurekalert.org/news-releases/953042. Published May 24, 2022. Accessed May 24, 2022.

Chen C, et al. Can Med Assoc J. 2022;doi:10.1503/cmaj.220068.