1/Evidence of #Airborne #SARSCoV2 traveling 12 floors of an apt building through the drainage system: 200+ residents in a wing of a high-rise were tested, revealing 9 infections. Those families lived in 3 vertically aligned flats connected by drainage pipes in the bathrooms

2/To confirm apt units are indeed connected, tracer gas was released into drainage system of one unit and shown to come out of the other. Evidence for alternative mechanisms of transmission (e.g. use of public spaces, elevators, etc..) could not be found.

3/Plausible scenario is infection through drainage system. While U-traps typically act as water seals in each bathroom's drainage system, if unused, they can dry out, allowing aerosols from one unit to travel to another.
Report: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7464151/

4/A separate study has also implicated the transmission of SARS-CoV-2 through the air ducts of a building in South Korea: https://twitter.com/AliNouriPhD/status/1341193351014572032?s=20