Association between long-term exposure to ambient air pollution and COVID-19 severity: a prospective cohort study.

Background: The tremendous global health burden related to COVID-19 means that identifying determinants of COVID-19 severity is important for prevention and intervention. We aimed to explore long-term exposure to ambient air pollution as a potential contributor to COVID-19 severity, given its known impact on the respiratory system.
Methods: We used a cohort of all people with confirmed SARS-CoV-2 infection, aged 20 years and older and not residing in a long-term care facility in Ontario, Canada, during 2020. We evaluated the association between long-term exposure to fine particulate matter (PM _2.5 ), nitrogen dioxide (NO ₂ ) and ground-level ozone (O ₃ ), and risk of COVID-19-related hospital admission, intensive care unit (ICU) admission and death. We ascertained individuals' long-term exposures to each air pollutant based on their residence from 2015 to 2019. We used logistic regression and adjusted for confounders and selection bias using various individual and contextual covariates obtained through data linkage.
Results: Among the 151 105 people with confirmed SARS-CoV-2 infection in Ontario in 2020, we observed 8630 hospital admissions, 1912 ICU admissions and 2137 deaths related to COVID-19. For each interquartile range increase in exposure to PM _2.5 (1.70 μg/m ³ ), we estimated odds ratios of 1.06 (95% confidence interval [CI] 1.01-1.12), 1.09 (95% CI 0.98-1.21) and 1.00 (95% CI 0.90-1.11) for hospital admission, ICU admission and death, respectively. Estimates were smaller for NO ₂ . We also estimated odds ratios of 1.15 (95% CI 1.06-1.23), 1.30 (95% CI 1.12-1.50) and 1.18 (95% CI 1.02-1.36) per interquartile range increase of 5.14 ppb in O ₃ for hospital admission, ICU admission and death, respectively.
Interpretation: Chronic exposure to air pollution may contribute to severe outcomes after SARS-CoV-2 infection, particularly exposure to O ₃ .
Competing Interests: Competing interests: Jeff Kwong is supported by a Clinician Scientist Award from the Department of Family and Community Medicine, University of Toronto. Chen Chen reports receiving salary support by the funding of this project, from Health Canada. Megan Kirby-Mcgregor reports receiving doctoral student funding from Health Canada, paid through McGill University. Jay Kaufman reports receiving payments from Health Canada (paid to institution) for student salaries and other research expenses associated with this work. Hong Chen reports receiving support for the present manuscript from Health Canada. No other competing interests were declared.
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