Hotels and Apartment Societies may have higher risk
Ventilation shaft is located along each vertical line where shafts connect to units through blowhole in bathrooms. Units built before installation of exhaust fans w/backdraft dampers became compulsory. Thus, there was no physical block for air entering the room from the air duct.
Study also implies that the rigid rules of safe distancing that stick to droplet and contact transmission based on an outdated dichotomous notion of respiratory droplet or aerosols should be reconsidered.
This also means higher risk for people living in apartment buildings , working in multi story offices and staying in hotels. Attached research more