According to a new American study, exposure to fine particles is partly responsible for the rapid spread of the SARS-CoV-2 virus in the United States.
- By analyzing areas of high SARS-oV-2 spread, the researchers found a correlation between R0 and PM2.5 exposure levels.
- In question: the presence of black carbon, or soot, which has an acute effect on lung health, and therefore makes it more vulnerable to infection with Covid-19.
Already implicated in the increase in the number of cancers, lung infections, heart or kidney disorders, fine particles emitted mainly by vehicle exhaust gases and industrial activity also play a role in the epidemic. of Covid-19.
This is the conclusion reached by researchers from the McKelvey School of Engineering at Washington University in St. Louis, who related the basic reproduction rate R0 of SARS-Cov-2 and the levels of ambient exposure to particles called PM 2.5 (PM for “Particulate Matter”). They publish their study in the journal Science of The Total Environment.
“We checked over 40 confounding factors”, explains Rajan Chakrabarty, lead author of the work. Among all these factors, “there was a strong linear association between long-term exposure to PM2.5 and R0”he says.
A correlation between pollution and viral replication
Representing about 3% of the diameter of a human hair, PM2.5 are airborne particles with a diameter of 2.5 micrometers or less. Which means they can enter the lungs and affect respiratory health.
Since the beginning of the epidemic, researchers have been exploring the relationship of fine particles and the Covid-19 pandemic. In July, an article in the magazine Science revealed that levels of susceptibility to Covid-19 are a determining factor in the pandemic. The following month, a new study published in the Journal of Infection revealed that the highest number of severe cases of Covid-19 were in places with higher pollution levels.
“I wondered why, in the majority of American states, the virus spread so quickly”, explains Professor Chakrabarty. With his team, he studied the places in the country where the R0 was greater than 1, that is to say when an infected patient transmits the disease to at least one other person. In these areas, 43 different factors were reviewed, including population density and age distribution. The researchers then used pollution estimates in the United States between 2012 and 2017 as the basis for their modeling.
They then found that an increase of almost 0.25 in R0 corresponded to a 10% increase in the composition of sulphate, nitrogen dioxide and ammonium, and an increase of 1 μg/m3 in PM2.5 concentrations.
Moreover, these correlations were strongest in places where pollution levels were well below the National Ambient Air Quality Standards (NAAQS), the levels of air pollutants considered safe for humans.
“National annual average PM2.5 standards are set at or below 12 micrograms per cubic meter, below what is thought to be safe, explains Professor Chakrabarty. What we’ve seen, the correlation we’re seeing is well below that standard.”
Air quality standards that prepare for a future pandemic
How can this increase in R0 be explained with the levels of exposure to PM2.5? For the authors of the study, there is a direct link between the risk of spreading the virus and the presence of black carbon, commonly known as soot. “We discovered that the black carbon acts as a kind of catalyst. In the presence of soot, PM2.5 has a more acute effect on lung health, and therefore on R0.”
For the study authors, there is an urgent need to better regulate air quality in the United States to reduce nitrogen dioxide levels, which impact the spread of the virus, even more so with “the recent reversal of environmental regulations that weaken limits on gaseous emissions from power plants and vehicles threatens the country’s future air quality scenario”.
“Instead of working to fix this problem, these reversals could prepare us for another pandemic”concludes Professor Chakrabarty.
