Over the last few days, there have been a lot of confusing statements made by the newscasters in describing the “how” Covid-19 infection is transmitted.

Unfortunately, the newscasters do not differentiate between a “lay person definition” and a “medical definition”, leading to the confusion.  In this time of crisis and anxiety, we need to be very careful with the terms we use.  As I repeatedly tell my students and residents, “words matter.”

So, buckle up, and get ready for a technical discussion of a mundane topic!

First, here are some “definitions”:

  • Aerosols and droplets:
    • These are particles which are “floating” in the air
    • Defined as particles that are <100 μm (micrometers) in diameter and are not visible to the naked eye
    • When they are greater than 5 μm in diameter, these particles are “too heavy” to remain floating in the air for any length of time, and rapidly fall to the ground
    • When they are smaller than 5 μm in diameter, these particles are “not heavy”, and remain floating in the air for a short amount of time, and very slowly fall to the ground
  • Airborne
    • These particles are also smaller than 5 μm in diameter
    • These particles are so small, and so “light” that they remain floating in the air for an extended period of time
    • While floating in the air, they can travel a greater distance

  • Infectious droplets:
    • Defined as larger infectious particles (>5 μm in diameter) that rapidly fall out of the air
    • Such droplets are not usually dispersed through the air.
    • Once they fall “out of the air”, they land on a surface.
    • When one touches the surface, the infection can spread.
    • Such a spread can be prevented by wearing gloves, and changing gloves in-between patient contacts.

  • Infectious aerosols:
    • Defined as small particles (<5 μm in diameter)
    • Since they are so small and “light”, they are suspended in the air for a brief amount of time
    • An example of an “aerosol” is a “sneeze” or “cough”
    • If you happen to have a respiratory infection, and then sneeze, the infectious particles are “blown” out with the sneeze, and “suspended” in the air for a short amount of time
    • These infectious particles can disperse throughout the air and environment and, while they are floating in the air, they remain infectious for a short amount of time
    • After a brief amount of time, these particles will slowly fall to the ground
    • Since the “sneeze” or “cough” is associated with “air being forced out of your mouth / nose”, these particles can travel a short distance and remain infectious
    • If these particles are inhaled by a bystander, it can lead to the transmission of the infection

  • Covid-19:
    • The Covid-19 virus is approximately 0.5 to 1.0 μm (micrometers)
    • Since Covid-19 is so small, it remains aerosolized for an unknown period of time
    • While the virus is “floating” in the air, a light wind can push it further away from the person that sneezed or coughed
    • The duration of time that Covid-19 remains aerosolized is NOT yet known
    • If (AND THIS IS A BIG IF), these aerosolized infectious Covid particles remain in the air for an extended period of time, then the infection is considered to be an “airborne pathogen”
      • If someone sneezes, these “airborne” Covid viruses remain in the air, and float around with the wind
      • Such a “floating” Covid can then infect another person who might be hundreds of feet away, or potentially miles away from the initial infected person
      • This is NOT yet proven, but only hypothesized
    • Since it is not yet known whether Covid can be “airborne”, as of March 31, 2020, the WHO has stated that Covid-19 is NOT an airborne pathogen
    • Obviously, with further scientific data, this classification can change


OK – got thru another confusing topic.

Stay safe!

  • Sudhir S. Athni, MD

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