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Updated 03.31. Is coronavirus transmitted through the air? What is known at the moment

Despite the fact that a new coronavirus infection has been actively spreading among people for almost two months, we still do not know much about it. One important, unclear point is whether the SARS-CoV-2 virus particles are able to remain in the air for a long time as an aerosol and subsequently retain the ability to become infected by inhalation. An understanding of the dynamics of the spread of infection and the adoption of adequate response measures depend on the answer to this question. In this article, I propose to consider the data obtained by researchers in this direction, as of March 31, 2020.

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Content


  • Aerobiology. Educational program
  • Airy or drip, what difference does it make and why should anyone care
  • What is known regarding SARS-CoV-2
  • Discussion
  • Update on 03/31/2020
  • Cited Works

Aerobiology. Educational program


The existing classification of transmission of infectious diseases by air distinguishes two main classes: airborne droplets and airborne dust, or in the English version - “droplet” and “airborne”, respectively. I propose to follow a more intuitive English terminology and to use the names - drip and airway, respectively, within the framework of this article. The World Health Organization defines airborne infections as capable of spreading through the air with aerosols containing droplets of less than 5 micrometers in diameter, and those diseases that are transmitted only by larger droplets are considered droplets [ 1 ] [ 2 p. 44].
1 micrometer - 1 µm, this is one thousandth of a millimeter

It is believed that particles larger than 5 micrometers, sprayed, for example, as a result of sneezing, are not able to stay in the air for a long time and soon settle under the influence of gravity. Drops less than 5 micrometers, in contrast, can be in the air for a long time, in the form of an aerosol, and move with the air currents. In addition to particle size, the ability of infections to be transmitted by air is influenced by many other factors, from molecular structure, temperature and humidity, to the amount of solar ultraviolet radiation and wind speed. The study of all the intricacies of the spread of microorganisms through the air is engaged in a special section of biology - Aerobiology [ 3 ].

Currently, for many pathogens, it is recognized that they are capable of being transmitted by air, for example, bacterial pathogens: pertussis, staphylococcus, and tuberculosis, and viruses such as influenza virus, chickenpox, rubella, as well as the precursor of coronavirus - SARS-CoV [ 4 ] [ 5 p. 117].

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A table of some common airborne pathogens. Source [ 4 , table 2]

Airy or drip, what difference does it make and why should anyone care?


The type of spread of infection depends on the necessary precautions and prevention.

Now the official version of WHO and the U.S. Centers for Disease Control and Prevention classifies the new coronavirus as droplet infection, that is, together with particles over 5 micrometers. [ 6 ] [ 7 ] The

size of the micro droplets emerging from the human respiratory tract ranges from <5 to 500 micrometers in diameter and depends primarily on respiratory activity, so that with normal calm breathing the smallest particles are formed and are much larger during coughing and sneezing. [ 4 , table 3]
If the infection spreads through the air only by the drip, then, as a rule, the droplets of the pathogens containing it exit during sneezing or coughing, such droplets will settle on the ground for a short time and within a radius of several meters. In this case, it is enough not to be too close to the infected person at the moment when he coughs or sneezes and to avoid contact with the flying particles, it is also effective to wear infected medical masks that are quite capable of retaining large particles.

If the infection is able to spread through the air in the form of an aerosol consisting of drops of less than 5 micrometers, which leave the respiratory tract constantly, during normal exhalation and are able to remain in suspension for a long time, then the situation is complicated and additional more serious measures are needed. In this case, the transmission of infection is possible when the infected person is in the same room, or even when inhaling air passing through a single ventilation system.

For clarity, I’ll give a video in which the researchers demonstrated using the Schlieren visualization method [ 9] the spread of air flow during various types of respiratory activity, such as: conversation between people, calm breathing, laughing, coughing and sneezing using a scarf, surgical mask and N95 mask Source [ 9 ].


What is known about SARS-CoV-2?


On March 3, the results of air sampling from the wards of 3 patients in a hospital in the outbreak area of ​​SARS-CoV-2 in Singapore were published, it is reported that although the virus was found in swabs from plumbing and furniture surfaces, no aerosol was found in the air intakes particles of the virus, although they were found on the details of ventilation. [ 10 ]

On March 10, a preprint of the work was published, with the results of analyzes of 35 air samples from three locations: Renmin Hospital of Wuhan University, from the Fangcang Deployed Field Hospital and from the Public Area (PUA) also in Wuhan. It is reported that in two cases, aerosol particles of the virus were not detected or there were only minor concentrations. But samples from the intensive care unit and air samples in the toilet of the Fangcang Hospital gave a positive result [11 ].

It is important to note that the studies above looked only for the genetic signature of the virus, that is, traces of RNA. To understand whether the virus from the air retained the ability to infect cells, it is necessary to seed the collected viral material into the cell culture and examine the results. The preprint of such a study was published on March 13, 2020, and the results were even more alarming. A material released with the support of the National Institute of Allergy and Infectious Diseases (NIAID) and the National Institute of Health (NIH) reports preliminary data on the particle stability of the new SARS-CoV-2 in aerosols and on various surfaces, in comparison with the closest SARS to it -CoV-1 [ 12 ].

The preprint means that the data has yet to be verified by experts, but so far the results do not look too comforting. Namely, it was shown that: SARS-CoV-2 remained viable in aerosols for 3 hours, with a decrease in the infectious titer from 10 ^ 3.5 to 10 ^ 2.7 TCID50 / L. It was also shown that the greatest viability time for coronavirus was observed on plastic surfaces - up to 48 hours.

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Comparisons of the titer measure TCID50 (vertical axis) of 2019-nCoV and SARS-CoV-1 coronaviruses in aerosols and on various types of surfaces. Horizontally postponed time in hours
[ 13 ].

: TCID50 – , 50, , , 10^2,7 TCID50/L – , 10^2,7≈500 , ( ) 50% . [14][15]



Understanding how the virus spreads is crucial for developing effective precautions and prevention for viral infections. While there is too little data on whether coronavirus is able to spread through the air in the form of an aerosol from one person to another, the studies that are available at the moment require expert verification. But one should take into account the likelihood that these data will be confirmed and, if possible, reduce their risks.

March 31, 2020 Patch



03/29/2020 The World Health Organization published on its website a scientific brief on nCoV-2019 transmission methods [ 16 ], which summarizes the currently available data.

The work reports that the transmission by aerogenous route, that is, with particles less than 5 micrometers, is possible only under certain conditions, when supporting procedures are carried out with an infected person that generate a large amount of aerosol containing viral particles. Among these procedures are listed: endotracheal intubation, bronchoscopy, open pumping of fluid from the lungs, the use of nebulizers, manual ventilation of the lungs before intubation, turning the patient to a lying position, disconnecting the patient from the ventilator, non-invasive ventilation with positive pressure, tracheostomy and cardiopulmonary resuscitation .

Therefore, WHO continues to recommend precautions against drip transmission for people caring for patients with COVID-19. And for procedures such as those listed above that generate aerosols, WHO recommends precautions against transmission by aerogenous route [ 17 ] [ 18 ], including: N95 or FFP2 respirator, eye protection, gloves, a bathrobe and apron .

Similar recommendations are also followed: European Intensive Care Society (ESICM) and Intensive Care Society (SCCM) [ 19]. At the same time, the U.S. Centers for Disease Control and Prevention () and the European Centers for Disease Prevention and Control, recommend aerogenic infection precautions for any patient care situation with COVID-19, but allow the use of a conventional surgical dressing in addition to goggles and gloves in case of shortage of N95 or FFP2 respirators [ 20 ] [ 21 ].

From the author. WHO notes that these recommendations may change as new data become available, so we will follow the updates. But judging by the data that are currently available, if you are not a medical professional and do not work in close contact with sick people who already exhibit COVID-19 symptoms, then there is no need for a daily respirator, high-grade protection. More important, in terms of preventing infection, is hand hygiene and control of contact with surfaces that may contain particles of the virus, as well as maintaining a distance of 1.5 - 2 meters from other people when in public places.

Cited Works
1. en.wikipedia.org/wiki/Airborne_disease
2. apps.who.int/medicinedocs/documents/s16355e/s16355e.pdf (. 44)
3. www.ncbi.nlm.nih.gov/pmc/articles/PMC3556854
4. https://www.journalofinfection.com/article/S0163-4453(10)00347-6/fulltext
5. stacks.cdc.gov/view/cdc/61187 (. 117)
6. www.who.int/ru/emergencies/diseases/novel-coronavirus-2019/advice-for-public/q-a-coronaviruses
7. www.cdc.gov/coronavirus/2019-ncov/prepare/transmission.html
8. en.wikipedia.org/wiki/Schlieren_photography
9. journals.plos.org/plosone/article?id=10.1371/journal.pone.0021392#authcontrib
10. jamanetwork.com/journals/jama/fullarticle/2762692
11. www.biorxiv.org/content/10.1101/2020.03.08.982637v1
12. www.medrxiv.org/content/10.1101/2020.03.09.20033217v2
13. www.medrxiv.org/content/10.1101/2020.03.09.20033217v2.full.pdf
14. studfile.net/preview/4659008
15. en.wikipedia.org/wiki/Virus_quantification
16. www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations
17. www.who.int/emergencies/diseases/novel-coronavirus-2019/technical-guidance/infection-prevention-and-control
18. apps.who.int/iris/bitstream/handle/10665/331498/WHO-2019-nCoV-IPCPPE_use-2020.2-eng.pdf
19. www.sccm.org/SurvivingSepsisCampaign/Guidelines/COVID-19
20. www.cdc.gov/coronavirus/2019-ncov/infection-control/control-recommendations.html#monitor_manage
21. www.ecdc.europa.eu/sites/default/files/documents/COVID-19-infection-prevention-and-control-healthcare-settings-march-2020.pdf

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