Study: Coronavirus Can Linger in the Air for Hours in Certain Places

London Tube Crowd

Getty Passengers squeeze on to a busy Central Line underground train at Stratford Station, east London, March 23, 2020. Amid the coronvirus pandemic transport officials have closed dozens of London Underground stations, but are maintaining the system to enable "critical workers to make essential journeys".

A new study out of Wuhan, China, found that coronavirus can linger in tiny droplets in the air in certain spaces, suggesting the virus may be spread through airborne transmission even when an infected person is no longer present.

While the virus’ ability to spread with seeming ease is still not fully understood, the Centers for Disease Control and Prevention and the World Health Organization have said transmission is believed to be caused by respiratory droplets of infected people getting into uninfected people through the mouth, nose or eyes, either directly through close contact or indirectly through surfaces. This is why the CDC and WHO advise people not to touch their faces.

The new study, published Monday in Nature, looked at aerosol transmission, more commonly referred to as airborne spread. Researchers discovered that the virus can linger in the air in crowded areas where there are infected people much longer than respiratory droplets do.

Both respiratory and aerosol droplets come out of our bodies when we do things like cough or sneeze,  but the big difference between respiratory droplets and the aerosol version — called droplet nuclei — is the size. Respiratory droplets are larger and sink relatively quickly, while aerosol droplets are much smaller and can stay afloat for hours.

According to the Bode Science Center, “Airborne droplet nuclei develop when the fluid of pathogenic droplets evaporate. They are so small and light they may remain suspended in the air for several hours. Thus, they may also infect persons entering a room which has been left by a patient long ago. Also, airborne droplet nuclei can be widely dispersed by air currents.”

The Study Found High Levels of the Virus Floating in the Air in Crowded Areas & Around Toilets

GettyA worker wears a protective suit as he disinfects a room in the Wuhan No.7 hospital in Wuhan, in China’s central Hubei province on March 19, 2020.

The research was done in two different areas of a hospital in Wuhan, China, the city where the virus originated. Scientists measured the aerodynamic nature of the virus during the COVID-19 outbreak in February and March 2020.

Researchers found different levels of the virus in different areas, saying the concentration of coronavirus “in isolation wards and ventilated patient rooms was very low, but it was elevated in the patients’ toilet areas.” The researchers did not offer an explanation as to why there would be higher concentrations around toilet areas, but the CDC has written that the virus has been found in the stool of infected patients.

The study also found that in the majority of public areas the virus was not detectable in the air, except for in two areas which were “prone to crowding.” Airborne levels of the virus were also high in medical staff areas, but after “rigorous sanitation procedures” in those areas the levels of coronavirus in the air became undetectable, giving credence to the effect good sanitation measures have on killing the coronavirus.

The Study’s Authors Say More Research Is Needed to Understand How Transmittible the Virus Is When in Aerosol Form

China Cherry Blossoms

GettyThis photo taken on March 17, 2018, shows a crowd of people with umbrellas looking at cherry blossoms at the Wuhan University in Wuhan in China’s central Hubei province.

While the researchers did find that the virus can live as an airborne pathogen, they did not mention whether anyone contracted the virus in the areas where the levels in the air were high.

The authors of the study wrote, “We propose that SARS-CoV-2 may have the potential to be transmitted via aerosols. Our results indicate that room ventilation, open space, sanitization of protective apparel, and proper use and disinfection of toilet areas can effectively limit the concentration of SARS-CoV-2 RNA in aerosols.” That information may also lend some credibility to another recent study which found that the virus is less transferable outdoors.

The WHO wrote on March 29, “According to current evidence, COVID-19 virus is primarily transmitted between people through respiratory droplets and contact routes. In an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported.”

The study’s researchers seem to think that maybe the jury is still out on the WHO’s assessment, writing, “Future work should explore the infectivity of aerosolized virus.”

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