Is COVID-19 infection an airborne disease?

12 Feb 2020 / Dr. Lee Chun Hui, David (General Practitioner)

Is COVID-19 infection an airborne disease?

  • Whether a pathogen is an airborne pathogen depends on a few factors: molecular structures and weight, pathogen's duration of suspension in air, and viability of the pathogen when exposed to an ambient environment.
  • It’s been proven that some pathogens are airborne pathogens, e.g. measles, TB, chickenpox.
  • However, there are other pathogens that can be airborne opportunistically – i.e. if given the “suitable environments”, the pathogen can be aerosolized and spread through air, e.g.  influenza virus.
  • “Suitable environments” usually involve some “forces” that propel the droplets which contain the pathogen (a virus in this case) into the air and spread to a distant location that is far away from the source.
  • These propelling “forces” usually are found in hospital/clinic settings, where highrisks procedures are performed, e.g. intubating a patient, high-flow oxygen and nebulized treatments, and suctioning and aspirating fluids from patients.
  • These procedures are not found in the community. However, under very specific circumstances, the propelling “forces” which may aerosolize a pathogen that is not inherently airborne may exist in our neighborhood, like in the case of SARS transmission in Amoy’s Gardens in 2003.
  • In the recent Tsing Yi’s Hong Mei House incident, there is a possibility that a broken vent pipe of the water closet had allowed the virus to backflow into the bathroom. Whether the virus was aerosolized in this incident is yet to be confirmed.
  • In another recent hotpot and BBQ family gathering incident, 19 people attended the gathering, and at least 10 of them have been confirmed positive for COVID-19 infection. Initially, it was rumored that the steam generated from the hotpot could have aerosolized the virus which infected many inside the room. However, this lacks scientific evidence to support, and many experts have already questioned this hypothesis.

How can we reduce the risk of contracting the infection from a potentially aerosolized COVID-19 in the washroom?

  • Filling U-shaped drainage pipe with at least 500ml of plain water (at least weekly).
  • Put the toilet lid down before you flush.
  • Check the integrity of the vent pipe of the water closet (if it's in your washroom, consider spraying soapy water over the pipe– if bubbles appear when you flush, there may be a leakage; if it's on the external wall of your home, discuss with your building management).

What can we learn from the hotpot and BBQ gathering incident?

  • Steam from the hotpot or smoke from the grill does not increase the risk of aerosolizing the virus.
  • In hotpot or BBQ gatherings, people are usually sitting very close to each other. Infected droplets may spread to people, drinks and food, or sauces nearby easily. Also, close contact with an infected person greatly increases the chance of contracting the infection.
  • As much as we enjoy being with our friends and relatives, we should cut down the unnecessary group gatherings for the time being.


Source: Dr. Lee Chun Hui, David (General Practitioner)