In the early days of the coronavirus pandemic, a team of scientists is called The World Health Organization acknowledges that the disease can be spread through the air.
Initially, the agency denied their request, despite growing evidence that the air contains droplets of the coronavirus, making indoor spaces a breeding ground for infection.The researchers’ response was public eventswhich helped convince the World Health Organization to finally admit at the end of 2021, Coronavirus is spread through the air.
In the wake of the controversy, the agency also asked a group of advisers, including some scientific critics, to update its formal guidance for classifying how the pathogen spreads.After more than two years of discussions, the group published a Report Creating a new definition could have significant implications for countries around the world that rely on the agency to develop policies to curb the spread of the disease.
The World Health Organization’s previous position was that only a few pathogens – those that spread in small droplets and travel long distances, such as tuberculosis – could be considered airborne. But the new report proposes a broader category that does not rely on droplet size or distance traveled. The changes are controversial because they signal that more diseases may now require costly control measures such as hospital isolation rooms and protective gear.
“This is an important first step,” said Dr. Ed Nadel, a tuberculosis expert at Harvard Medical School and a member of the panel. “We do have a start, there are agreed-upon terms, even if everyone is not happy with it.”
Before the outbreak, the World Health Organization and other agencies usually recognized Several ways disease spreads. One is through “contact transmission,” where someone becomes infected with the pathogen through direct contact with an infected person or through contact with a contaminated surface.
“Droplet transmission” involves the short-range spread of disease when people cough or sneeze, producing droplets larger than 5 microns (five millionths of a meter), which then land directly on the victim’s mouth, eyes or nose.
“Airborne” refers to a small number of diseases that are spread by droplets smaller than 5 microns, which can float great distances until someone inhales them.
The agency said when the new coronavirus emerges, it is likely to spread over short distances through contact or droplet transmission.
But Li Yuguo, a mechanical engineer at the University of Hong Kong, and many other critics worry that the WHO is ignoring the possibility of airborne transmission of the new coronavirus. As the epidemic progresses, scientists are uncovering evidence in the outbreak that the coronavirus may indeed be able to spread long distances through floating droplets. (Some scientists question the strength of these studies. )
The World Health Organization established a new advisory group in November 2021 and invited Dr. Li to serve as co-chairman. At the panel’s meeting, Dr. Lee and others argued that the agency relied on a false dichotomy.
For example, the 5-micron threshold for small droplets has little scientific basis. Larger water droplets can also float for long periods of time.
The researchers also believe that short-term infection does not prove that the disease is spread only through coughing and sneezing. An infected person can also exhale droplets by breathing or talking, which can then be inhaled by others nearby.
The new report divides transmission routes into contact transmission and airborne transmission. The group agreed to call the second route “transmission by air.”
Linsey Marr, an environmental engineer at Virginia Tech and a member of the advisory group, finds the phrase more awkward than simpler terms such as airborne.
“I found it very bulky,” she said. “But we’re looking for lowest common denominator terms that everyone can accept.”
The report further states that pathogens can be spread through the air in two ways. One is “direct deposition,” where droplets hit the mucous membranes of the mouth, eyes, or nose. The other is “airborne/inhalation”, where the droplets are inhaled.
After scientists proposed the new terminology, the World Health Organization obtained agreement from the U.S. Centers for Disease Control and Prevention and counterparts in Africa, China and Europe to use the same definition.
“This is a very important statement of cooperation agreement,” said Dr. Jeremy Farrar, chief scientist at the World Health Organization.
But the new report makes no recommendations on how agencies should prevent the disease from spreading through these different pathways. The authors acknowledge that they were unable to reach consensus on this issue.
Traditionally, hospital guidelines for controlling airborne diseases have called for costly measures such as negative pressure isolation rooms, as well as N95 respirators and other protective gear to avoid inhaling fine droplets. But it’s unclear which diseases require such control, or what efforts should be undertaken outside the hospital.
Dr. Walter Singer, an infectious disease expert at the University of Zurich and a member of the advisory panel, said the old categories provided more direct guidance. For example, it was once thought that staying a few feet away from people who were coughing and sneezing was an effective way to avoid droplet transmission.
“It’s simple and may not be correct to some extent, but it serves its purpose,” he said. “Now we have to bring other variables to the table.”
Dr Farrar said such guidance should be based on clear experimental evidence, although for many diseases this evidence is still sparse. For example, scientists still debate the extent to which influenza, which has been studied for more than a century, spreads through the air.
“We know a certain amount, but we can’t be absolutely certain,” Dr. Farrar said. “This is what we urgently need to do against influenza.”