Ambient fine particulate matter air pollution and the risk of hospitalization among COVID-19 positive individuals: Cohort study

Background: Ecologic analyses suggest that living in areas with higher levels of ambient fine particulate matter air pollution (PM_2.5) is associated with higher risk of adverse COVID-19 outcomes. Studies accounting for individual-level health characteristics are lacking. Methods: We leveraged the breadth and depth of the US Department of Veterans Affairs national healthcare databases and built a national cohort of 169,102 COVID-19 positive United States Veterans, enrolled between March 2, 2020 and January 31, 2021, and followed them through February 15, 2021. Annual average 2018 PM_2.5 exposure, at an approximately 1 km² resolution, was linked with residential street address at the year prior to COVID-19 positive test. COVID-19 hospitalization was defined as first hospital admission between 7 days prior to, and 15 days after, the first COVID-19 positive date. Adjusted Poisson regression assessed the association of PM_2.5 with risk of hospitalization. Results: There were 25,422 (15.0%) hospitalizations; 5,448 (11.9%), 5,056 (13.0%), 7,159 (16.1%), and 7,759 (19.4%) were in the lowest to highest PM_2.5 quartile, respectively. In models adjusted for State, demographic and behavioral factors, contextual characteristics, and characteristics of the pandemic a one interquartile range increase in PM_2.5 (1.9 µg/m³) was associated with a 10% (95% CI: 8%–12%) increase in risk of hospitalization. The association of PM_2.5 and risk of hospitalization among COVID-19 individuals was present in each wave of the pandemic. Models of non-linear exposure–response suggested increased risk at PM_2.5 concentrations below the national standard 12 µg/m³. Formal effect modification analyses suggested higher risk of hospitalization associated with PM_2.5 in Black people compared to White people (p = 0.045), and in those living in socioeconomically disadvantaged neighborhoods (p < 0.001). Conclusions: Exposure to higher levels of PM_2.5 was associated with increased risk of hospitalization among COVID-19 infected individuals. The risk was evident at PM_2.5 levels below the regulatory standards. The analysis identified those of Black race and those living in disadvantaged neighborhoods as population groups that may be more susceptible to the untoward effect of PM_2.5 on risk of hospitalization in the setting of COVID-19.