Is it safe to use aerosolizing devices outside? 

Posted on March 31, 2020 by Ellison Richmond

Summary

Aerosolizing devices and procedures in uncontrolled environments present unpredictable risk of droplet transmission. Environmental considerations such as humidity, temperature, and airflows will affect this risk

I.   AIRBORNE OR DROPLET TRANSMISSION?

  • The WHO states that COVID-19 virus is primarily transmitted via respiratory droplets and physical/surface contact. They state droplet transmission must be within 1 meter contact of a patient with respiratory symptoms, with exposure to another person’s mucosae or conjunctiva (1)
  • The US CDC recommends Airborne Infection Isolation Rooms are used for COVID-19 patients undergoing aerosol-generating procedures. (2)
  • A study of environmental conditions of SARS-CoV-1 and SARS-CoV-2 found  SARS-CoV-2 remained viable in aerosol over 3 hours (the duration of the experiment), with a half-life of about 1.2 hours. (By comparison, this study found median half-life was about 5.6 hours on stainless steel and 6.8 hours on plastic.) (3)
  • Experts have voiced concern that the possibility for airborne transmission of SARS-CoV-2 has been downplayed. (4)

II.   DROPLETS AND AIRFLOWS

  • Air sampling and swabbing of exhaust outlets of a Singapore facility suggested small virus-laden droplets may be displaced by airflows. Viability of these viral samples was not determined. (5)
  • High-momentum clouds (e.g. airflows, sneezes and coughs) which carry droplets may far outstretch recommendations for 1 to 2 meters, with exhalation alone able to create clouds up to 7 or 8 meters. (6)

III.   DROPLET TRANSMISSION AND AEROSOLIZATION IN DIFFERENT ENVIRONMENTS

  • At least one review article has identified that transmission from aerosol-generating procedures varies greatly by environment (7), suggesting that field hospitals and less-controlled environments present unpredictable aerosol dynamics.
  • No safety guidelines for aerosol-generating procedures in outdoor environments were found, suggesting that for patients with transmissible diseases this is not considered safe.
  • Innovations have been recently proposed to increase safety for procedures such as intubation, such as plexiglass boxes (8) or plastic bags (9) as shields. These have not been evaluated for safety.

Questions? Comments? Does this need to be updated? Do you have valuable points to add ? Please email ask.reakt@ubc.ca.

References

  1. World Health Organization: WHO. Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations [Internet]. Who.int. World Health Organization: WHO; 2020 [cited 2020 Apr 1]. Available from: https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations
  2. CDC. Infection Control: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [Internet]. Centers for Disease Control and Prevention. 2020 [cited 2020 Apr 1]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/infection-control/control-recommendations.html
  3.  van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. New England Journal of Medicine [Internet]. 2020 Mar 17 [cited 2020 Apr 1]; Available from: https://www.nejm.org/doi/10.1056/NEJMc2004973
  4.  WHO Reviews “Current” Evidence On Coronavirus Transmission Through Air [Internet]. NPR.org. 2020 [cited 2020 Apr 1]. Available from: https://www.npr.org/2020/03/28/823292062/who-reviews-available-evidence-on-coronavirus-transmission-through-air
  5.  Ong SWX, Tan YK, Chia PY, Lee TH, Ng OT, Wong MSY, 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 [Internet]. 2020 Mar 4 [cited 2020 Apr 1]; Available from: https://jamanetwork.com/journals/jama/fullarticle/2762692
  6.  Bourouiba L. Turbulent Gas Clouds and Respiratory Pathogen Emissions. JAMA [Internet]. 2020 Mar 26 [cited 2020 Apr 1]; Available from: https://jamanetwork.com/journals/jama/fullarticle/2763852
  7. Judson SD, Munster VJ. Nosocomial Transmission of Emerging Viruses via Aerosol-Generating Medical Procedures. Viruses [Internet]. 2019 Oct 12 [cited 2020 Apr 1];11(10):940. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6832307/
  8. YouTube.  https://www.youtube.com/watch?v=b3lZ2n-_P_g
  9. Twitter. 2020 [cited 2020 Apr 1]. Available from: https://twitter.com/StephenLap/status/1242087577978646539

Disclaimer

The above is intended to serve as a rapidly-created, accessible source of information curated by medical students and healthcare professionals. It is for educational purposes only and is not a complete reference resource. It is not professional medical advice, and is not a substitute for the discretion, judgment, and duties of healthcare professionals. You are solely responsible for evaluating the information above.