Is COVID-19 Airborne?

August 3, 2020

This is a summary from our recent review of a Grand Rounds presentation provided by UCSF titled: “How the virus gets in, and how to block it: Aerosols, Droplets, Masks, Face Shields and more.” 

Takeaway: People with SARS-CoV-2 shed virus in small enough particles to spread through the air, but distance, decreased duration of exposure and mask use all decrease the likelihood of an infectious particle making it into your body. 

This portion is given by Don Milton, MD, DrPH.  Professor, Environmental & Occupational Health, University of Maryland School of Medicine.  Dr Milton has dedicated his life to research on how viruses travel through the air. He is unquestionably a qualified speaker on this topic. He covers some background information that might be helpful when we talk about masks and face shields later. 

For simplicity, I will use these two names interchangeably for the duration of this summary.  This, of course, does not constitute medical advice nor does it create a doctor-patient relationship between you (the reader) and me.

Transmission Models

From his explanation transmission modes of respiratory viruses fall into three general categories (Contact, Splash/Spray and Inhalation), dependent in part, on the size of the viral particle:

  • Contact: patient to finger; fomite (fancy word for material like a door knob) to finger; finger to eye, nose or mouth.  For example, a person coughs on his or her hand, shakes yours and then you pick your nose.  Now the virus is in your body. 
  • Splash and spray: ballistic drops (greater than 100 microns in size) direct hit on eye, nostril, and/or mouth.  For example, someone sneezes on you and some viral particles land in your eye.  Now the virus is in your body. 
  • Inhalation: inhalable aerosols (less than 100 microns in size).  For example, a person with an infection coughs or sneezes. While you do not have direct contact with the person or their saliva, you may walk through the same area and breathe in some viral particles. Now the virus is in your body. 

Is Airborne Spread of COVID-19 Happening?

COVID-19 virus particles can be very small.  A study from Singapore identified aerosol particles as small as one to four microns. 

A study from Wuhan China  was able to identify viral RNA in the air in very small particle sizes as well.

The size of the viral particles have several implications for how far a virus particle can travel in the air, and for how far it can go into the body. When the COVID-19 virus gets into the body, it needs to bind to certain receptors. Once bound they can enter cells and replicate.  We have several locations in the body where SARS-CoV-2 can bind, most notably in the mouth, lungs, and eyes. 

Knowing this as business owners, we can decide how we want to protect our workers and customers who enter our place of business. While we think its important to have a pre-work employee health screening process in place. We think business owners should consider solutions beyond mask use for workers and maybe even patrons.

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