Long-term air pollution and other risk factors associated with COVID-19 at the census tract level in Colorado

Abstract

Previous nationwide studies have reported links between long-term concentrations of fine particulate matter (PM2.5) and COVID-19 infection and mortality rates. In order to translate these results to the state level, we use Bayesian hierarchical models to explore potential links between long-term PM2.5 concentrations and census tract-level rates of COVID-19 outcomes (infections, hospitalizations, and deaths) in Colorado. We explicitly consider how the uncertainty in PM2.5 estimates affects our results by comparing four different PM2.5 surfaces from academic and governmental organizations. After controlling for 20 census tract-level covariates, we find that our results depend heavily on the choice of PM2.5 surface. Using PM2.5 estimates from the United States EPA, we find that a 1 μg/m³ increase in long-term PM2.5 concentrations is associated with a statistically significant 26% increase in the relative risk of hospitalizations and a 34% increase in mortality. Results for all other surfaces and outcomes were not statistically significant. At the same time, we find a clear association between communities of color and COVID-19 outcomes at the Colorado census tract level that is minimally affected by the choice of PM2.5 surface. A per-interquartile range (IQR) increase in the percent of non-African American people of color was associated with a 31%, 43%, and 56% increase in the relative risk of infection, hospitalization, and mortality respectively, while a per-IQR increase in the proportion of non-Hispanic African Americans was associated with a 4% and 7% increase in the relative risk of infections and hospitalizations. The current disagreement among the different PM2.5 estimates is a key factor limiting our ability to link environmental exposures and health outcomes at the census tract level. These results have strong implications for the implementation of an equitable public health response during the crisis and suggest targeted areas for additional air monitoring in Colorado.

Keywords: Air pollution; COVID-19; Disparity; Equity; PM2.5; SARS-CoV-2.

Graphical abstract

Fig. 1

Comparison of the four different PM2.5 surfaces over the state of Colorado and in the Denver metro area.

Fig. 2

Unadjusted effect of a 1 μg/m³ increase in long-term average PM2.5 concentration on three COVID outcomes, depending on the source of PM2.5 surface and model specification.

Fig. 3

Estimated effect of a 1 μg/m³ increase in long-term average PM2.5 concentration on three COVID outcomes, from fully adjusted models.

Fig. 4

Effect estimates for all covariates included in the model. Points represent the estimated mean and thin lines represent the 95% confidence interval. Shapes indicate the COVID-19 outcome considered and colors the PM2.5 surface used. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)