Long-term exposure to air pollution and COVID-19 mortality and morbidity in Denmark (AIRCODEN)

Background: Evidence on long-term exposure to air pollution and morbidity and mortality from coronavirus disease (COVID-19) is still sparse and inconclusive. We examined the association between long-term exposure to air pollution and COVID-19 incidence, hospitalization, and mortality. Methods: 3,721,813 subjects who were 30 years or older and resided in Denmark on March 1st, 2020 were followed for first COVID-19 positive test (incidence)/hospitalization/death until April 26th, 2021. We assigned annual mean concentrations to residential addresses in 2019, including particulate matter with a diameter <2.5 µm (PM2.5), nitrogen dioxide (NO2), black carbon (BC), and ozone (O3) estimated using 1x1km DEHM/UBM model. We linked air pollution levels with COVID-19 outcomes using random-effect (frailty) Cox proportional hazard models, adjusting for age, sex, and individual-level socioeconomic status (SES) (income, housing, occupation, marital status) with cluster term for parish. Additional analyses with adjustment for parish-levels SES will be presented at ISEE2022. Results: During 411–417 follow-up days, 138,742 individuals got tested positive for COVID-19, 11,270 were admitted to a hospital, and 2,557 died from COVID-19. PM2.5, NO2 and BC, but not O3, were significantly associated with COVID-19 mortality with hazard ratios (HRs) and 95% confidence intervals of 1.18 (1.10-1.27) per 0.53 μg/m3 increase in PM2.5, 1.82 (1.64-2.03) per 3.59 μg/m3 increase in NO2, and 1.10 (1.05-1.14) per 0.09 μg/m3 increase in BC. Somewhat weaker associations were found for COVID-19 related hospitalizations, with HRs of 1.21 (1.17-1.26) for PM2.5, 1.70 (1.60-1.81) for NO2, and 1.09 (1.05-1.13) for BC, and weakest with COVID-19 incidence, with HRs of 1.18 (1.15-1.21) for PM2.5, 1.55 (1.49-1.62) for NO2, and 1.09 (1.05-1.13) for BC. HRs for all-cause mortality were 1.02 (1.01-1.03) for PM2.5, 1.04 (1.02-1.06) for NO2, and 1.02 (1.01-1.03) for BC. Conclusion: Long-term exposure to air pollution was associated with COVID-19 related morbidity and mortality. Keyword: Air pollution, COVID-19, hospitalization, incidence, mortality