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US study shows increase of only 1 g/m3 in PM2.5 is associated with 15% COVID-19 death rate increase

Coronavirus patients in areas that had high levels of air pollution before the pandemic are more likely to die from the infection than patients in cleaner parts of the country, according to a new nationwide study that offers the first clear link between long-term exposure to pollution and Covid-19 death rates.

Exposure to air pollution and COVID-19 mortality in the United States Xiao Wu MS, Rachel C. Nethery PhD, M. Benjamin Sabath MA, Danielle Braun PhD, Francesca Dominici PhD All authors are part of the Department of Biostatistics, Harvard T.H. Chan School of Public Heath, Boston, MA, 02115, USA

Updated April 5, 2020 Exposure to air pollution and COVID-19 mortality in the United States Xiao Wu MS, Rachel C. Nethery PhD, M. Benjamin Sabath MA, Danielle Braun PhD, Francesca Dominici PhD All authors are part of the Department of Biostatistics, Harvard T.H. Chan School of Public Heath, Boston, MA, 02115, USA Lead authors: Xiao Wu and Rachel C. Nethery Corresponding and senior author: Francesca Dominici, PhD Clarence James Gamble Professor of Biostatistics, Population and Data Science Harvard T.H. Chan School of Public Health Co-Director Harvard Data Science Initiative 677 Huntington Avenue Boston, MA 02115 410.258.5886 Email:

Abstract Background: United States government scientists estimate that COVID-19 may kill between 100,000 and 240,000 Americans. The majority of the pre-existing conditions that increase the risk of death for COVID-19 are the same diseases that are affected by long-term exposure to air pollution. We investigate whether long-term average exposure to fine particulate matter (PM2.5) increases the risk of COVID-19 deaths in the United States. Methods: Data was collected for approximately 3,000 counties in the United States (98% of the population) up to April 04, 2020. We fit zero-inflated negative binomial mixed models using county level COVID-19 deaths as the outcome and county level long-term average of PM2.5 as the exposure. We adjust by population size, hospital beds, number of individuals tested, weather, and socioeconomic and behavioral variables including, but not limited to obesity and smoking. We include a random intercept by state to account for potential correlation in counties within the same state. Results: We found that an increase of only 1 g/m3 in PM2.5 is associated with a 15% increase in the COVID-19 death rate, 95% confidence interval (CI) (5%, 25%). Results are statistically significant and robust to secondary and sensitivity analyses. Conclusions: A small increase in long-term exposure to PM2.5 leads to a large increase in COVID-19 death rate, with the magnitude of increase 20 times that observed for PM2.5 and all- cause mortality. The study results underscore the importance of continuing to enforce existing air pollution regulations to protect human health both during and after the COVID-19 crisis. The data and code are publicly available. Introduction The scale of the COVID-19 public health emergency is an unmatched one in our lifetime. It will have grave social and economic consequences. The suddenness and global scope of this pandemic has raised urgent questions that require coordinated and credentialed information to slow its devastation. A critically important public health objective is to identify key modifiable environmental factors, such as ambient air pollution, that could increase the severity of the health outcomes (e.g., ICU hospitalization and death) among individuals with COVID-19. Our understanding of what causes death in COVID-19 patients is evolving. Early data from China suggests that a majority of COVID-19 deaths occurred in adults aged 60 years and among persons with serious underlying health conditions.1,2 Preliminary analyses of outcomes among COVID-19 patients in the United States largely agree, reporting the highest fatality rates in persons aged 65. A report by last month’s joint World Health Organization3 reported that one in seven patients develops difficulty breathing and other severe complications. These patients typically suffer respiratory failure and failure of other vital systems. COVID-19 can cause viral pneumonia with additional extrapulmonary manifestations and complications including acute respiratory distress syndrome (ARDS) which has a mortality rate ranging from 27% to 45%.4 Factors associated with mortality include sex (male), advanced age ( 65), and the presence of comorbidities including hypertension, diabetes mellitus, cardiovascular diseases, and cerebrovascular diseases. COVID-19 is also associated with a high inflammatory burden that can induce vascular inflammation, myocarditis, and cardiac arrhythmias.5 Although the epidemiology of COVID-19 is evolving, we have determined that there is a large overlap between causes of deaths of COVID-19 patients and the diseases that are affected long-term exposure to fine particulate matter (PM2.5). The Global Burden of Disease Study identified air pollution as a risk factor for total and cardiovascular disease mortality and is believed to be responsible for 5.5 million premature deaths worldwide a year.6 PM2.5 contains microscopic solids or liquid droplets that are so small they can be inhaled and cause serious health problems. On Thursday, March 26, 2020 the US EPA announced a sweeping relaxation of environmental rules in response to the coronavirus pandemic, allowing power plants, factories and other facilities to determine for themselves if they are able to meet legal requirements on reporting air and water pollution. We hypothesize that because long-term exposure to PM2.5 adversely affects the respiratory and cardiovascular system, it can also exacerbate the severity of the COVID-19 infection symptoms and may increase the risk of death in COVID-19 patients. The association between PM2.5 and health including pregnancy outcomes, respiratory diseases, cardiovascular diseases, neurocognitive disease in the United States and worldwide is well established.7,8,9,10,11,12 A recent study by our group also documented a statistically significant association between long-term exposures to PM2.5 and ozone and risk of ARDS among older adults in the United States.13 Numerous scientific studies reviewed by the US Environmental Protection Agency (US EPA) have linked PM2.5 to a variety of health concerns including: premature death in people with heart or lung disease, non-fatal heart attacks, irregular heartbeats, aggravated asthma, decreased lung function, and increased respiratory symptoms such as inflammation, airway irritations, coughing, or difficulty breathing.14 Our study includes 3,080 counties in the United States and covering 98% of the United States population. We leverage our previous efforts that focused on estimating the long-term effects of PM2.5 on mortality among 60 million United States’ Medicare enrollees.15,16,17 We used a well- tested research data platform that gathers, harmonizes, and links nationwide air pollution data, census data, and other potential confounding variables with health outcome data. We augment this platform with newly collected COVID-19 data from authoritative data sources.18 All data sources used in these analyses, along with fully reproducible code, are publicly available to facilitate continued investigation of these relationships as the COVID-19 outbreak evolves and more data become available. Data and Code:

Our data and code is available on github here.

Manuscript and Supplemental Material

- Citation: Exposure to air pollution and COVID-19 mortality in the United States. Xiao Wu, Rachel C. Nethery, Benjamin M. Sabath, Danielle Braun, Francesca Dominici. medRxiv 2020.04.05.20054502; doi:


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