Scientists warn of an invisible threat with Covid-19 ramifications

Even when we can't see it, the air we breathe profoundly shapes our health. Breathing dirty air can damage the lungs and heart — it may also worsen chances of surviving Covid-19.

That revelation stems from a "pathfinding" new study that compared air pollution levels and Covid-19 death rates of 3,089 U.S. counties. The researchers discovered that relatively small increases in bad air were linked with troubling Covid-19 outcomes.

On average, just one microgram per cubic meter in a county’s long-term exposure to fine particle pollutants was associated with an 11 percent increase in the county’s Covid-19 mortality rate.

The study was published Wednesday in the journal Science Advances.

These early findings aren't iron-clad in controlling for individual risk factors. But they do suggest tighter air pollution standards can prevent unnecessary lives lost to Covid-19.

They are also prescient: Also on Wednesday, the Trump administration officially exited the Paris Agreement — the global climate accord that aims to bring down greenhouse gas emissions and in turn, reduce air pollution. In light of these new findings, casting off the Agreement could put communities living in areas with high air pollutant exposure — particularly low income and marginalized communities— at even further risk of dying from Covid-19.

Air experiment — The study team began with a suspicion that air pollution might heighten the risk of severe Covid-19.

Typically, testing that suspicion would involve the long term study of detailed health datasets for "very large numbers of people from all walks of life and locations," scientists who were not involved in the study wrote in a related editorial. But because the researcher team was working with a unique time constraint — wanting to have answers that could help people now — they were unable to do that.

Instead, they went a different path, and analyzed air pollution data and Covid-19 mortality rates from 3,089 U.S. counties, focusing on fine particles of PM2.5. These are toxic particles with a diameter of fewer than 2.5 micrometers and can harm the respiratory and cardiovascular systems.

Co-author Xiao Wu, a biostatistician at Harvard University, tells Inverse that this type of air pollution is so dangerous precisely because it is so tiny.

"PM2.5 can penetrate deeply into the lung, irritate and corrode the alveolar wall, and consequently impair lung function," Wu says.

"They can further travel via the circulatory system, causing lung and heart problems and delivering harmful chemicals to the blood system."

Wu and his colleagues aggregated PM2.5 concentration estimates at the county level and averaged them between 2000 to 2016. Then they rounded up cumulative county-level Covid-19 death counts through June 18, 2020.

The scientists also utilized a statistical method called ecological regression to search for correlations within the data, accounting for many area-level factors including: population size, age distribution, population density, time since the beginning of the outbreak, and time since states' issuance of stay-at-home orders.

How does air pollution influence Covid-19?

The team found that higher historical fine-particle air pollution exposure and increased vulnerability to death from COVID-19 rates went hand in hand.

Importantly, the findings don't suggest air pollution makes people any more likely to become infected by Sars-CoV-2.

Instead, air pollution leaves a wake of bodily damage that appears to heighten the risk of developing severe Covid-19, once people catch the virus.

Although this study found this striking correlation, scientists still haven't pinned down the underlying mechanisms driving this dynamic. Some theorize that chronic air pollution exposure might cause ACE2 receptors — Covid-19's favorite infection entry points — to overexpress. This can impair the body's ability to defend itself against the virus.

Further experiments will shed light on how, exactly, dirty air influences people's ability to survive Covid-19. But for now, this study and other evidence suggest tightening air pollution standards can help mitigate this harmful effect.

The current situation — Despite years of warning about the pervasive health costs of toxic air from scientists, U.S. political officials have continually weakened environmental regulations on air pollution and carbon emission. In the past four years, the Trump administration has reversed 21 air pollution and emission regulations.

In April, amid the Covid-19 pandemic, the Environmental Protection Agency also proposed to maintain current standards for fine-particulate pollution, despite evidence and advice from government and academic scientists who have overwhelmingly backed tighter regulations, Wu says.

"This is an irresponsible move given air pollution as one of the modifiable factors may exacerbate Covid-19 symptoms and increase mortality risk," Wu says.

"This scientific evidence should guide policies and behaviors to minimize fatality related to the pandemic. I would say, 'let the science speak.'"

Abstract: Assessing whether long-term exposure to air pollution increases the severity of COVID-19 health outcomes, including death, is an important public health objective. Limitations in COVID-19 data availability and quality remain obstacles to conducting conclusive studies on this topic. At present, publicly available COVID-19 outcome data for representative populations are available only as area-level counts. Therefore, studies of long-term exposure to air pollution and COVID-19 outcomes using these data must use an ecological regression analysis, which precludes controlling for individual-level COVID-19 risk factors. We describe these challenges in the context of one of the first preliminary investigations of this question in the United States, where we found that higher historical PM2.5 exposures are positively associated with higher county-level COVID-19 mortality rates after accounting for many area-level confounders. Motivated by this study, we lay the groundwork for future research on this important topic, describe the challenges, and outline promising directions and opportunities.