Urban Air Pollution May Enhance COVID-19 Case-Fatality and Mortality Rates in the United States

Abstract

Background: The novel human coronavirus disease 2019 (COVID-19) pandemic has claimed more than 600,000 lives worldwide, causing tremendous public health, social, and economic damages. Although the risk factors of COVID-19 are still under investigation, environmental factors, such as urban air pollution, may play an important role in increasing population susceptibility to COVID-19 pathogenesis.

Methods: We conducted a cross-sectional nationwide study using zero-inflated negative binomial models to estimate the association between long-term (2010-2016) county-level exposures to NO₂, PM_2.5, and O₃ and county-level COVID-19 case-fatality and mortality rates in the United States. We used both single- and multi-pollutant models and controlled for spatial trends and a comprehensive set of potential confounders, including state-level test positive rate, county-level health care capacity, phase of epidemic, population mobility, population density, sociodemographics, socioeconomic status, race and ethnicity, behavioral risk factors, and meteorology.

Results: From January 22, 2020, to July 17, 2020, 3,659,828 COVID-19 cases and 138,552 deaths were reported in 3,076 US counties, with an overall observed case-fatality rate of 3.8%. County-level average NO₂ concentrations were positively associated with both COVID-19 case-fatality rate and mortality rate in single-, bi-, and tri-pollutant models. When adjusted for co-pollutants, per interquartile-range (IQR) increase in NO₂ (4.6 ppb), COVID-19 case-fatality rate and mortality rate were associated with an increase of 11.3% (95% CI 4.9%-18.2%) and 16.2% (95% CI 8.7%-24.0%), respectively. We did not observe significant associations between COVID-19 case-fatality rate and long-term exposure to PM_2.5 or O₃, although per IQR increase in PM_2.5 (2.6 μg/m³) was marginally associated, with a 14.9% (95% CI 0.0%-31.9%) increase in COVID-19 mortality rate when adjusted for co-pollutants.

Discussion: Long-term exposure to NO₂, which largely arises from urban combustion sources such as traffic, may enhance susceptibility to severe COVID-19 outcomes, independent of long-term PM_2.5 and O₃ exposure. The results support targeted public health actions to protect residents from COVID-19 in heavily polluted regions with historically high NO₂ levels. Continuation of current efforts to lower traffic emissions and ambient air pollution may be an important component of reducing population-level risk of COVID-19 case fatality and mortality.

Keywords: COVID-19; air pollution; case-fatality rate; mortality; nitrogen dioxide.

Graphical abstract

Figure 1

County-Level COVID-19 Case-Fatality and Mortality Rates County-level COVID-19 case-fatality rate (A) and mortality rate per 1 million people (B) as of July 17, 2020.

Figure 2

County-Level Annual Average Concentrations of Nitrogen Dioxide, Fine Particulate Matter, and Ozone County-level annual average concentrations of NO₂ (A), PM_2.5 (B), and ozone (C) for the period 2010–2016.

Figure 3

Percentage Change in County-Level COVID-19 Case-Fatality Rate and Mortality Rate Percentage change in county-level COVID-19 case-fatality rate (A) and mortality rate (B) per interquartile range (IQR) increase in long-term air pollutant concentrations. Effect estimates and 95% confidence intervals were calculated using county-level concentrations of nitrogen dioxide (NO₂, orange), ozone (purple), and fine particulate matter (PM_2.5, blue) averaged between 2010 and 2016, controlling for covariates including county-level number of cases per 1,000 people, social deprivation index, population density, percentage of residents over 60 years of age, percentage of males, race and ethnicity, body mass index, smoking rate, number of regular hospital beds per 1,000 people, number of intensive unit beds per 1,000 people, number of medical doctors per 1,000 people, average mobility index assessed between March and July 17, 2020, average temperature and humidity between January 22 and July 17, 2020, state-level COVID-19 test positive rate as of July 17, 2020, and spatial smoother with 5 degrees of freedom for both latitude and longitude. IQRs of NO₂, PM_2.5, and O₃ averaged between 2010 and 2016 were 4.6 ppb, 2.6 μg/m³, and 3.3 ppb, respectively.

Figure 4

Percentage Change in COVID-19 Case-Fatality Rate in the Sensitivity Analysis Percentage change in COVID-19 case-fatality rate per interquartile range increase in NO₂ (A), PM_2.5 (B), and ozone (C) concentrations in the sensitivity analysis. The red line denotes the estimated effects in the main analysis. All results were derived from the tri-pollutant models. Recent 4 weeks refers to June 20 to July 17.

Figure 5

Percentage Change in COVID-19 Mortality Rate in the Sensitivity Analysis Percentage change in COVID-19 mortality rate per interquartile range increase in NO₂ (A), PM_2.5 (B), and ozone (C) concentrations in the sensitivity analysis. The red line denotes the estimated effects in the main analysis. All results were derived from the tri-pollutant models. Recent 4 weeks refers to June 20 to July 17.