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Has there been evidence that a sick person on one floor could infect someone on another floor through the ventilation system?

Question: To follow up from yesterday’s Q&A: We know that lots of people in the same room and poor ventilation is bad, but what about someplace like a hotel or office building? Has there been evidence that a sick person on one floor could infect someone on another floor through the ventilation system?

Answer: There is currently only very weak evidence of airborne transmission across floors of an office building or apartment building. Bulleted below are a few examples, though it is by no means an exhaustive list. As I understand it, most experts believe that the data are not strong enough to definitely say that airborne transmission through ventilation systems is happening, but that the current level of evidence is compelling enough to warrant concern and to necessitate further study. The big debate is over what action to take in light of limited evidence. For further discussion, in addition to links shared in yesterday’s post, see the report of Canada’s Rapid Expert Consultation on Airborne Transmission, these two recent JAMA viewpoint articles, and this report from Nature. Should we implement additional safety control measures (examples are bulleted in yesterday’s post), which can be costly or wait until we know more? Should we be more cautious at greater financial cost or less cautious at possibly greater health/life cost?

  • The experience of a call center outbreak in Seoul points to airborne spread — the initial case worked on the 10th floor and had no contact with workers on the 11th floor who subsequently were infected.
  • The experience of Hong Mei House in Hong Kong points to airborne spread — the first two people in the building to contract SARS-CoV-2 were in the same vertical block of apartments, but 10 floors apart and some experts believed the likely culprit was a broken exhaust pipe.
  • Meanwhile, last month another apartment complex in Hong Kong, the Sha Tin public housing estate, was evacuated as experts feared a new cluster of cases stemmed from the sewage system.
  • Looking at a different, but similar virus, SARS-CoV (of 2003), we have stronger evidence from the Amoy Gardens housing complex that points to the spread coming from a”rising plume of contaminated warm air in the air shaft generated from a middle-level apartment unit.”