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New coronavirus may spread as an airborne aerosol, like SARS

woman with nebulizer
(Image: © Shutterstock)

Editor's note: The study described in this article was published in The New England Journal of Medicine on March 17. This article was originally published on March 13.    

The novel coronavirus SARS-CoV-2 can survive in the air for several hours in fine particles known as aerosols, according to preliminary research. 

The coronavirus, which causes the respiratory infection COVID-19, can be detected up to 3 hours after aerosolization and can infect cells throughout that time period, the study authors found. The study, first posted March 10 on the preprint database medRxiv, is still preliminary, because it has not undergone extensive peer-review. The authors did receive comments from one prospective scientific journal, and posted an updated version of the study on March 13 reflecting the revisions.

Assuming these initial results hold up to scrutiny, aerosol transmission of SARS-CoV-2 appears "plausible," the authors wrote — but several key questions remain unanswered.

"We still don't know how high a concentration of viable SARS-CoV-2 is needed in practice to infect a human being, though this is something we are looking to model in the future," co-author Dylan Morris, a graduate student in the Department of Ecology and Evolutionary Biology at Princeton University, told Live Science in an email. Morris and his colleagues tested whether viral particles from aerosols could infect cells grown in the lab, not actual human beings. More important, even if aerosol transmission can occur, it's unlikely to be the primary force driving the current pandemic, Morris added.

"The current scientific consensus is that most transmission via respiratory secretions happens in the form of large respiratory droplets ... rather than small aerosols," he said. "Droplets, fortunately, are heavy enough that they don't travel very far" and instead fall from the air after traveling only a few feet.  

Aerosols, by contrast, can potentially travel across far greater distances; the virus that causes chickenpox, for example, can travel tens of yards from an infected person and incite secondary infections elsewhere in the environment, and can remain in an area even after the person who emitted them has left. However, in the current study, the researchers did not examine how far SARS-CoV-2 could conceivably travel through the air.

Related: 10 deadly diseases that hopped across species 

Viral survival 

To see how long SARS-CoV-2 survives as an aerosol, the researchers fed samples of the virus through a nebulizer and sprayed the aerosolized particles into a drum-like structure. They then took periodic samples from the drum and analyzed each one for viral genetic material, known as RNA.

The team was able to detect viral RNA throughout the course of their 3-hour experiment, but that alone does guarantee that the remaining virus was viable.

"You find an RNA on a surface, that doesn't mean that the virus … could infect somebody," said Aubree Gordon, an associate professor of epidemiology at the University of Michigan School of Public Health, who was not involved in the study. To determine whether the virus was truly viable, the researchers grew the germ in cultured cells. These critical tests rendered the study "much stronger" than if the researchers had only looked for RNA, Gordon said. 

The team also tracked how levels of the virus decayed over time by noting how its concentration declined from sample to sample. Using these measurements, they calculated the "half-life" of a virus in different environments, or how long it takes for the viral concentration to decrease by half.

"A basic principle of [viral] decay is that if you start out with more virus, you'll have detectable virus for longer," Morris said. "The estimated half-lives give us a sense of how long things would last if we started with different initial concentrations." In other words, knowing the half-life of a virus allows scientists to determine how long a particular virus can survive in different environments, regardless of how much virus happens to be present at the time of sampling. 

Aerosolized virus showed a median half-life of about 1.1-1.2 hours, similar to the related coronavirus that causes SARS, the authors noted.  

The team also examined how long the virus remains viable on copper, stainless steel, plastic and cardboard. Viable virus could not be detected on copper after 4 hours, or after 24 hours on cardboard. The germ survived best on plastic and stainless steel, remaining viable for up to 72 hours, although its overall concentration fell significantly by that time. The half-life of the virus varied on each surface, as well; the virus showed a half-life of about 0.8 hours on copper, 3.46 hours on cardboard, 5.6 hours on steel and 6.8 hours on plastic.

The cardboard measures might raise eyebrows because many packages shipped through the mail are made of cardboard. But, while 24 hours sounds like a long time, Morris said that the authors "advise caution" in interpreting these results. "Our cardboard data were notably noisier than our data from other surfaces," meaning the results differed noticeably when they repeated the experiment, he said. 

Additionally, "we do not know how much virus is actually needed to infect a human being with high probability, nor how easily the virus is transferred from the cardboard to one's hand when touching a package," he added.

What would aerosol transmission really mean for spread? 

The notion of viral particles hanging in the air, ready to infect passersby, may seem scary, but to become an aerosol, droplets containing viral particles must first be transformed into a light mist, thin enough to be supported by the air. By definition, aerosols are less than 0.0002 inches (5 microns) in diameter, while typical respiratory droplets exceed this size. 

"Based on what we know about other respiratory viruses, we don't think that SARS-CoV-2 gets aerosolized in everyday settings," Morris said. "Rather, aerosolization, if it happens at all for SARS-CoV-2, is likely to happen in health care settings," according to recent studies, Morris said.

During the SARS outbreak in 2002-2003, aerosols drove severe bouts of viral spread in health care settings, Gordon said.

Specifically, the use of intubation — where a tube is inserted into a patient's windpipe — and nebulizers — which transform medicines into an inhalable mist — generated aerosols and increased the risk of viral transmission to health care providers, she said. Additionally, aerosols released in stool likely drove two SARS superspreader events in non-health care settings, one in an apartment complex and the other in a hotel, she said.    

If inhaled, fine aerosols often travel deeper into the body than heavy respiratory droplets, and spark severe infection in the lungs, she added. 

She and other experts already assumed that aerosol transmission of SARS-CoV-2 "may be a concern, because we had seen that with SARS," Gordon said. While the new study supports their speculations, she said that scientists should be "cautious" about how they interpret the results. 

"We want to see if we do see virus in the air in health care settings," she said. In other words, samples of actual hospital air must be taken to determine if SARS-CoV-2 aerosols are present at significant levels, and what that means for health care providers and their patients.

Originally published on Live Science. 

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  • Sarrueche
    Bekim BACAJ said:
    How interesting...
    On Saturday, February 29, 2020 @ 8:13 AM I wrote:

    "The novel coronavirus SARS-CoV-2, which causes the COVID-19 disease, is not a naturally occurring strain of disease. It's spread this far ( has been assisted by the "12 Monkeys" globalist network, and ) is fully unnatural. "

    "Because 2019-CoV-2 is artificially enabled to infect humans utilizing molecules of SARS penetration mechanism, its 19th generation infection coefficient is still a lab controlled environment successful, it (SARS-CoV-2) still cannot infect humans on its own successfully ( Or at the desirable rate for which it was created ).

    Alas, once it gets hold onto some decadent community; especially a "sanctuary city", and "the defecate cities" run by democrat liberals. SARS-CoV-2 will get a chance to start reproducing in a living host - the reproduced virion that gets to successfully infect another body, it will become fully autonomous and airborne."
    :: This is only a reiteration of my previous post from Monday, January 27, 2020 @ 7:04 AM
    That was about 3 days before the name of this novel corona virus was decided and since I wrote this :: "The monster on the loose is actually an strand — Bekim BACAJ ©" Yes, with the copy mark, it's final name came out somewhat different "SARS-CoV-2"

    So you're saying the coronavirus was created in a lab in China and transmitted to the United States?
  • Marek
    admin said:
    However, it's unlikely that the virus would spread in this way beyond health care settings.

    New coronavirus may spread as an airborne aerosol, like SARS : Read more
    In my opinion corona virus can be sorbed on the dust particles present in the air and therefore can travel with the dust on the long distances, i.e. several hundred metres. The dry air with suspension of the dust is especially dangerous, since the adsorption of virus is very probaable. In wet air the dust will gravitationallly fall down in the form of big particles.
  • Johann A.G. Baloghy
    Marek said:
    In my opinion corona virus can be sorbed on the dust particles present in the air and therefore can travel with the dust on the long distances, i.e. several hundred metres. The dry air with suspension of the dust is especially dangerous, since the adsorption of virus is very probaable. In wet air the dust will gravitationallly fall down in the form of big particles.

    I aggre with you under "meteorological influences" e.g. Wind.
    Please read this:
    by Johann A.G. Baloghy
  • Johann A.G. Baloghy
    by Johann A.G. Baloghy
    Some physical aspects of Corona-µ-Aerosols, which are set into homogeneous movements by the air flow as an influencing factor.Link:µ-aerosole-physikalische-aspekte-der-johann-a-g-baloghy/
  • Marek
    Dear Sir,

    Interesting hypothesis. I think that the sorption of polypeptides by the dust is the new challenge for the physical chemistry!
  • Johann A.G. Baloghy
    Marek said:
    Dear Sir,

    Interesting hypothesis. I think that the sorption of polypeptides by the dust is the new challenge for the physical chemistry!

    Good day Sir,

    absolutely correct and I agree!

    For the transition from the hypothesis to verification and evidence, I would suggest:
    A. Wind tunnel simulations in the laboratory, for the behavioral investigation of ultrafine particles, with 0.06 - 0.14 µm micrometer aerodynamic diameter, loaded in "droplets", to determine the changes in the physical properties of these and to gain further knowledge.
    The wind air for testing must also contain a mix of dust and particles of components, as they actually in the reality occur!
    Different temperatures must also be taken into account.
    B. Safe field simulations also in cities, hospitals, production facilities, barracks, settlements and apartments, ..., etc.

    Four major factors can contribute to the further spread of viruses in the air under the influence of the wind (meteorological influences):
    1. loss of gravity effect,
    2. weight loss of the particles due to evaporation of the water content of the "droplets",
    3. quote: "Particles with a size of up to about 1 μm float in the air for several days. They are constantly in motion, being pushed back and forth and attached to other particles. In this way, larger particles capture smaller particles (scavenging effect). " . (see my Article)
    4. Viral survival of the possible e.g. "Corona-µ-Aerosole" clouds.

    My best of regards,
    Johann A.G. Baloghy
  • Johann A.G. Baloghy

    1. COVID-19 transmitted via aerosol "in certain conditions"
    2. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1
    3. The new coronavirus can likely remain airborne for some time. That doesn’t mean we’re doomed
    4. Study tracks coronavirus aerosol spread – but there’s some good news
    5. Novel Coronavirus Can Survive in Aerosol Form and on Hard Surfaces for Hours to Days, Study Reveals
    Assessing the Dynamics and Control of Droplet- and Aerosol-Transmitted Influenza Using an Indoor Positioning System
  • Mcnurse
    Is anyone else not at all comforted by the statement about it not being likely outside of healthcare settings? Especially if you are a Healthcare worker?