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The WHO says the coronavirus is not airborne - but some research suggests otherwise

Aylin Woodward , Business Insider US
 Apr 03, 2020, 01:52 PM

  • The new coronavirus typically spreads when droplets from an infected patient coughs or sneezes, and the droplets land on or get inhaled by another person.
  • According to the World Health Organization, the Covid-19 virus is not airborne, like measles, and does not spread between people who are more than 1.8 metres apart.
  • Some research, however, suggests that viral droplets can travel farther than 1.8 metres in certain conditions, and that live coronavirus can persist in the air in aerosol form.
  • Such aerosols pose a disproportionate risk to people in hospital settings.
  • Visit Business Insider's homepage for more stories.

As researchers race to study the coronavirus, an important question remains hotly debated: Can it spread through the air?

Scientists agree that the virus, which has infected more than 1 million people worldwide, is primarily transmitted through droplets - particles larger than 5 micrometers - when an infected person coughs, sneezes, or speaks.

Those droplets, of course, fly through the air before landing on another person. But scientists still aren't sure to what degree a cloud of tiny viral particles - known as aerosols (these are smaller than droplets) - could linger in the air, waiting to infect the next person who walks through the same space. This is known as airborne transmission, and the measles virus is known to spread that way - it lives for up to two hours in an airspace where an infected person coughed or sneezed.

But the World Health Organization says that's not the case for the coronavirus.

"FACT: #COVID19 is NOT airborne," the WHO tweeted on March 28.

However, several recent studies have identified live coronavirus in the air. The Centers for Disease Control and Prevention warns that certain hospital procedures, like intubating a patient, "could generate infectious aerosols".

Droplets versus aerosols

The main difference between droplets and aerosols is that the former are heavy and large, so they can't stay aloft for long. The latter, called droplet nuclei by the WHO, are smaller than 5 micrometres.

But some researchers are calling for the semantics to be swept aside to avoid confusion and better inform public-health responses to the pandemic.

"I think the WHO is being irresponsible in giving out that information. This misinformation is dangerous," Donald Milton, an infectious-disease aerobiologist at the University of Maryland, told NPR.

He added: "The epidemiologists say if it's 'close contact,' then it's not airborne. That's baloney."

Some research shows the coronavirus can travel further than 1.8 metres, the distance cited by the CDC as adequate social distancing.

"Vigorous coughing or sneezing, during which a patient gives their exhalation more energy, can send their microscopic particles beyond the 2-foot to 6-foot range [0.6 - 1.8 metres]," William Schaffner, a professor of preventive medicine and infectious diseases at Vanderbilt University, told Business Insider.

A study published March 26 in the Journal of the American Medical Association found that a cloud of virus emitted by someone coughing or sneezing could travel much farther than 1.8 metres: "The gas cloud and its payload of pathogen-bearing droplets of all sizes can travel 23 to 27 feet [7 - 8 metres]," it said.

'You could come into a room thinking everything's all right and then you inhale it'

During a recent interview on "The Daily Show," host Trevor Noah asked Dr. Anthony Fauci - director of the National Institute of Allergy and Infectious Diseases - whether the coronavirus stays in the air.

"If you walk in to an elevator after somebody else, can coronavirus still be there?" Noah said.

Fauci replied that ill people sneezing and coughing can spread the virus by droplets as well as by aerosols.

An aerosolised form of the virus "means the drop doesn't go down right away, it hangs around for a bit," Fauci said, adding, "so you could come into a room thinking everything's all right and then you inhale it."

But he noted that aerosol transmission is likely not the primary way the coronavirus spreads and reiterated that social distancing of 1.8 metres is sufficient to protect yourself.

Schaffner agreed that in Noah's elevator example,"in such a tightly enclosed space without vigorous air movement for a short period of time, I'm afraid you might be exposed."

But that's a different situation than, say, a supermarket, which is fairly large and in which air moves freely.

"The kinds of transient encounters walking up and down the aisle picking up peaches not really hazardous," Schaffner said.

In lab settings, the virus can linger in the air for 3 hours

A recent study from the National Institutes of Health looked at how long the new coronavirus can live on common surfaces, and found that it can live in the air as an aerosol for up to three hours. But those researchers used a high-powered laboratory machine to produce the coronavirus aerosols, so they likely weren't identical to those produced by human coughs.

Linsey Marr, an expert on aerosol transmission at Virginia Tech, told the New York Times that an aerosol released at a height of about 1.8 metres should fall to the ground after 34 minutes. She also said the amount of the virus that lingers in the air as an aerosol is likely too small to infect someone.

"It sounds scary," she said, "but unless you're close to someone, the amount you've been exposed to is very low."

Aerosol transmission in hospitals

Because healthcare workers are exposed to higher concentrations of the virus, they face more risk of catching it from both droplets and aerosols.

When coronavirus patients need a ventilator, doctors insert a tube into their airway, and that procedure inevitably generates infectious aerosols.

Hospital clinicians get into protective equipment before testing patients for the coronavirus at Newton-Wellesley Hospital in Newton, Massachusetts on March 18, 2020.

One study (which has yet to be peer-reviewed) examined two Chinese hospitals and found low levels of the coronavirus in the air in patients' rooms. Higher airborne concentrations were recorded in medical-staff areas, particularly in places where doctors removed protective gear. The authors wrote that virus-laden aerosols were probably deposited on protective gear like masks and gowns while the doctors worked, then sent back into the air when the staff shook those items as they stripped down.

"Surface sanitisation of the apparel before they are taken off may also help reduce the infection risk for medical staff," the authors wrote.

Scientists also detected the virus in the air outside patients' rooms at the University of Nebraska Medical Center.

Staff at an N95 mask production workshop of the Naton Medical Group in Beijing, China, March 11, 2020.

"If you think you're doing aerosolizing procedures in a healthcare setting, don't use your surgical mask. Use an N95," Schaffner said.

N95 masks filter out airborne particles smaller 0.3 microns. If the coronavirus weren't airborne, those masks wouldn't be as essential.

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