COVID-19 Transmission

Topic Progress:

Pearls for Transmission in COVID-19

1. We are still learning about the transmission of COVID-19.
2. Best available evidence has shown COVID-19 transmission are from droplet/contact.
3. Fomite transmission (contact) is often forgotten and thought to be a major contributor to disease transmission.

Why This Matters to Nurses

Is coughing and sneezing droplet or airborne? How much of the virus is shedding? Nobody can agree. The best way to look at is: How much virus are you likely and actually exposed to?

  • Someone talking to you normally 1 meter away.
  • Doing a nasopharyngeal swab, knowing full well the person could sneeze when you put a swab in their nose.
  • An actively coughing patient who is critically ill.

There is no one solution.

Point-Of-Care Risk Assessment (PCRA) Given the amount of uncertainty around COVID-19 and the current threat to health care workers across Canada, the Canadian Federation of Nurses Unions (CFNU) recognizes the critical importance of the point-of-care risk assessment (PCRA), an activity that is based on the individual nurses’ professional judgment (i.e., knowledge, skills, reasoning and education). Underlying the PCRA is the principle that individual health care workers are best positioned to determine the appropriate personal protective equipment (PPE) required based on the situation and their interactions with an individual patient. Read more about it here.

For example: If a guideline calls for droplet precautions but a patient is actively sneezing and coughing, escalate your PPE to airborne.

See Justin Morgenstern’s excellent post on aerosols, droplets and airborne spread.



COVID-19 is a novel coronavirus and is known to be spread by droplets (Eg. Sneezing, coughing) from one person and the other breathes it in1-4. The virus is carried on droplets and gains access to a person via mucous membranes, such as the eyes, mouth and nasal passages.

The USA CDC has published questions into spread beyond droplet1. See COVID-19 Controversies below.


Often overlooked in COVID-19 is fomite transmission. When droplets fall onto a surface (such as tables and door handles), someone touches the said surface and later touches their mucous membranes2. This is indirect contact transmission.


When we do aerosol-generating medical procedures (AGMP)1-4, we create micro droplets that can gain entry into our mucous membranes if we are not protected. For this reason, airborne precautions are recommended.

Examples of AGMP:
-Nebulized medications

Resus Tonight Podcast

If you like podcasts, Resus Tonight reviewed the literature surrounding PPE and transmission.

COVID-19 Transmission Controversies

Follow your local guidelines.

And inform yourself with data.

Shiu et a6 argue that, despite the presence of aerosolized virus in the air, it is unknown if the virus in the air can cause infection and if airborne precautions would be effective. This has been looked at for seasonal and avian influenza, Middle East Respiratory Syndrome and Respiratory Synctial Virus.

Although the USA CDC, WHO, Canada and ANZICS1-4 guidelines state that infection via airborne transmission can occur; however, the WHO, Canadian and ANZICS guidelines recommend droplet precautions unless there is potential or actual AGMP in a suspected or confirmed patient with COVID-19. The USA CDC recommends airborne precautions at all times for patients with suspected or confirmed COVID-19. The USA CDC guidelines have been updated to suggest a surgical mask is an appropriate alternative when N95 masks or alternatives are not available.

Doremalen et al’s7 letter to the editor sparked a media frenzy when they found, in their lab-controlled setting that when COVID-19 is mechanically aerosolized the virus can stay in the air and on surfaces longer than we expected. This research letter should be taken with caution given that it is performed in a controlled setting attempting to mimic reality and the authors do not consider it direct evidence of airborne transmission.

Meanwhile, Ong et al8 found patients in negative pressure rooms who were confirmed to have COVID-19 did not have virus particles detected in the air samples, but the virus particles were found in the air ducts. Furthermore, they found the virus particles were found on surfaces, such as light switches, toilets, bed rails among others.

Guo et al9 took swabs of environmental surfaces in ICU and on general wards and found the virus was widely distributed on floors, computer equipment, trash cans, handrails and in the air.

So what does this all mean?

Take a balanced approach when thinking of COVID-19 transmission. Recognize that good, quality data is scarcely available. Be skeptical of what you read and hear!


  1. CDC. (2020). Indirect virus transmission in cluster of COVID-19 cases, Wenzhou, China, 2020. Emerging Infectious Diseases.
  2. WHO. (2020). Infection prevention and control during health care when novel coronavirus (nCoV) infection is suspected.
  3. Government of Canada. (2020). Coronavirus disease (COVID-19): For health professionals.
  4. ANZICS. COVID-19 Guidelines.
  5. Pyankov et al. (2018). Survival of aerosolized coronavirus in the ambient air. Journal of Aerosol Science.
  6. Shiu EYC, Leung NHL, Cowling BJ. Controversy around airborne versus droplet transmission of respiratory viruses: implication for infection prevention. Curr Opin Infect Dis. 2019;32(4):372–379. doi:10.1097/QCO.0000000000000563
  7. Doremalen et al. Aerosol and surface stability of SARS-CoV-2 as Compared with SARS-CoV1. New England Journal of Medicine. 2020.
  8. Ong SWX, Tan YK, Chia PY, et al. Air, Surface Environmental, and Personal Protective Equipment Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) From a Symptomatic Patient. JAMA. Published online March 04, 2020. doi:10.1001/jama.2020.3227
  9. Guo Z-D, Wang Z-Y, Zhang S-F, Li X, Li L, Li C, et al. Aerosol and surface distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards, Wuhan, China, 2020. Emerg Infect Dis. 2020 Jul [date cited].

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