As the United States struggles to contain the coronavirus epidemic, scientists are finding that air pollution is making things even worse. In a study submitted for publication, researchers at Harvard University found that even a small increase in long-term exposure to PM2.5, or particulate matter with a diameter of 2.5 micrometers or less, can lead to a large increase in the death rate from COVID-19, the illness caused by the novel coronavirus.
Air Quality in a Time of Crisis
With over 460,000 cases in the United States, coronavirus-related deaths are approaching 20,000 and could reach about 60,400 by early August, according to the latest projection from the Seattle-based Institute for Health Metrics and Evaluation. Although the mechanisms of COVID-19 are still being investigated, the World Health Organization reported that one in seven patients develops difficulty breathing and other severe complications.
PM2.5, meanwhile, has been associated with health problems such as premature death, heart attacks, asthma, and airway irritations. However, in March, the Environmental Protection Agency said it was relaxing air pollution enforcement rules and allowing power plants, factories, and other facilities to skip pollution tests.
Scientists have long known about the effects of air pollution on public health. A severe smog event in London in 1952, for example, is believed to have caused about 12,000 deaths. Four years later, the United Kingdom’s Clean Air Act came into force and prohibited burning polluting fuels in designated areas, setting the stage for similar legislation overseas.
The researchers from Harvard’s T.H. Chan School of Public Health noticed that many conditions known to contribute to more severe COVID-19 outcomes are also known to be caused by long-term PM2.5 exposure. Seeking possible connections, they used an environmental health data platform they had already compiled that featured nationwide PM2.5 and socioeconomic and demographic information. They then added the incoming COVID-19 outcome data to the mix.
They analyzed data from 3,080 counties in the United States; adjusted for variables including population size, number of people tested, weather, obesity, and smoking; averaged PM2.5 exposure over 2000–2016; and looked at COVID-19 deaths as the outcome. The data account for 90% of confirmed COVID-19 deaths in the United States as of 4 April 2020. In the study, which has been submitted to the New England Journal of Medicine, the researchers determined that an increase of only 1 microgram (μg) per cubic meter (m3) of PM2.5 is associated with a 15% increase in the COVID-19 death rate.
“We found that people living in counties in the United States that have experienced higher levels of air pollution over the past 15–20 years have a substantially higher COVID-19 mortality rate,” said study coauthor Rachel C. Nethery, an assistant professor of biostatistics at Harvard. “Based on our findings, we would expect a county with PM2.5 levels of 15 μg/m3 (highly polluted) to have approximately 4.5 times higher COVID-19 death rate than a county with PM2.5 levels of 5 μg/m3 (low pollution), assuming the counties are similar aside from the difference in pollution levels.”
Relaxing Rules the “Wrong Choice”
The results of the study, which is the first nationwide report of its kind in the United States, are not surprising given epidemiological findings on air pollution for diseases such as severe acute respiratory syndrome (SARS), but the effect of PM2.5 on mortality could be dramatic, said University of Southern California environmental epidemiologist and biostatistician Zhanghua Chen, who was not involved with the study.
“Even though the findings were based upon the ongoing development of the pandemic and we cannot exclude the possibility that there are potential confounders that are not adjusted for, the findings of this paper lay out straightforward information that we should make all efforts to improve air quality so that we can reduce the total number of deaths from disasters like COVID-19,” said Chen. “The current EPA’s action on the relaxation of environmental rules in terms of pollutant emissions from power plants, factories, and other facilities is an obviously wrong choice and could result in more COVID incidences and deaths.”
Nethery said many people have been asking how they can limit the harmful impacts of air pollution during the epidemic. Her team plans to examine the effects of short-term air pollution exposure in COVID-19 as well as the disease’s relationships with race and poverty.
—Tim Hornyak (@robotopia), Science Writer