Disparities in PM2.5 exposure and population density influence SARS-CoV-2 transmission among racial and ethnic minorities

There is overwhelming evidence that minority populations across the United States (US) have been disproportionately affected by the coronavirus (COVID-19) pandemic. While the disparities are clear, the reasons underlying the rapidity of disease spread-characterized by the basic reproduction ratio R (0)-in these communities are less so. Here, we investigate the relative impact of disparities in socioeconomic, environmental, and lung health factors on R (0) across 12 major metropolitan statistical areas (MSAs) in the US at the county-level. We inferred county-level R (0) values using an established metapopulation epidemiological model corresponding to the period 1 March-30 April 2020 marked by a rapid surge in COVID-19 cases across the US and implementation of strict lockdown measures. We find that disparities in long-term, ambient PM2.5 exposure (particulate matter with aerodynamic diameter 2.5 mu m or less) and population density have an outsized effect on R (0) in comparison to disparities in the other factors. We also find that the effect of increasing population density on R (0) is dependent on ambient PM2.5 mass concentrations. PM2.5 exposure has a well-established causal effect with increased risks and severe outcomes during previous infectious disease outbreaks. Overall, we find the largest disparities in PM2.5 exposure, population density, and associated increase in R (0) among the Hispanic-American population, followed by Asian-American and African-American populations, respectively. Longstanding geographic segregation of minority communities has led to extremely large fluctuations in county-level racial and ethnic minority fractions. As such, we conclude by providing each MSA with a roadmap for identifying which communities should be targeted for PM2.5 mitigation policy implementation. The methodology and results of this study may be extrapolatable to the rest of the world toward discerning the consequences of population density and PM2.5 disparities in COVID-19 spread.