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In Brief

CDC finally acknowledges airborne COVID-19 spread, for real this time

A magnifying glass over CDC's logo online.
(Image: © Shutterstock)

The Centers for Disease Control and Prevention (CDC) has updated its COVID-19 guidance to acknowledge that the virus can sometimes spread via "airborne transmission," or small droplet particles that linger in the air for long periods.

The revised guidance follows the CDC's blunder last month, in which the agency seemingly acknowledged airborne spread only to delete the information from its website two days later, Live Science previously reported. At the time, the CDC said that a draft version of the guidance had been posted in error, and that it was still working on its updated recommendations.

But now, the new guidance appears finalized. On Monday (Oct. 5), the agency officially announced it had updated the information on its "How COVID-19 Spreads" website to address airborne spread.

The website states that "some infections [of COVID-19] can be spread by exposure to virus in small droplets and particles that can linger in the air for minutes to hours. These viruses may be able to infect people who are further than 6 feet [1.8 meters] away from the person who is infected or after that person has left the space." 

Related: 14 coronavirus myths busted by science

Studies show that this type of spread can happen under certain conditions, specifically "enclosed spaces that had inadequate ventilation," the website says. 

Still, the new guidance seems to deemphasize aerosol spread as compared with the earlier draft guidance that was mistakenly posted. That draft guidance said that COVID-19 could spread through "respiratory droplets or small particles, such as those in aerosols," and noted that "this is thought to be the main way the virus spreads." 

The agency's new guidelines stress that aerosols are not the main way that COVID-19 spreads. "Available data indicate that it is much more common for the virus that causes COVID-19 to spread through close contact with a person who has COVID-19 than through airborne transmission."

Overall, the CDC said it's guidance on how to protect yourself from COVID-19 hasn't changed, according to a statement from the agency. "People can protect themselves from the virus that causes COVID-19 by staying at least 6 feet away from others, wearing a mask that covers their nose and mouth, washing their hands frequently, cleaning touched surfaces often and staying home when sick," the statement said.

The agency's website includes an additional recommendation to "avoid crowded indoor spaces and ensure indoor spaces are properly ventilated by bringing in outdoor air as much as possible."

Originally published on Live Science.  

  • Chem721
    It is somewhat mystifying that this issue went through any variations. It is, and was, well known that aerosols can infect people at considerable distance from the infected individual, who is venting virion-laden particles into the air (1).

    Vocalizing by speaking, yelling and singing are the most efficient means by which small particles form and vent from an infected person. The vocal cords, rapidly vibrating, is an ideal mechanism for generating very fine particles, and send them immediately out into the air. Small particles can drift considerable distances (2), and remain suspended in the air for extended periods. They are quite small, ranging from ca. 1 um to 5 um, and perfect for deep lung penetration.

    Quoting from (2):

    "Aerosols are generally poly-dispersed droplets and particles which have many different sizes. Classical airborne aerosol hygiene research described droplets of respiratory secretions evaporating to become “droplet nuclei”, which remain suspend in air currents or turbulence and may drift away considerable distances (>1 m) (Keene, 1955). Modern researchers generally use the phrase “droplet nuclei” to refer to respiratory aerosol droplets with aerodynamic diameter <5 μm, and some disease transmission research now refers to respiratory droplets in this size range as “aerosols”. Particles and droplets with aerodynamic diameter <5 μm have the ability to readily penetrate deep into the alveolar region of the lungs of a bystander (Buonanno et al., 2020). In contrast, relatively large droplets are thought to arise from the upper respiratory tract and settle quickly and relatively close to their source."

    end quote

    There is no doubt this virus can be spread by very fine particles emitted from an infected and shedding individual. To be sure, it is likely to be a very significant source of infectivity. People need to think about how they might minimize aerosol-generated particles in order to minimize viral spreading. Simply lowering voice levels could have a significant advantage in enclosed spaces. Loud voices and singing should be banned when conditions dictate a need for minimal aerosols.

    This form of infection - by aerosols - is one of the reasons masks play such a critical role in minimizing viral transmission.

    The science tells us that a mask might save your life, or others from you.


    "Aerosol emission and superemission during human speech increase with voice loudness"

    (1) https://www.nature.com/articles/s41598-019-38808-z

    "Aerosol transmission of SARS-CoV-2? Evidence, prevention and control"

    (2) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7413047/
    Reply