Verve Condominiums in Calgary, Alberta outbreak with cluster of 55+ cases on higher floors along the same side of the building suggest airborne transmission through ventilation systems.
Leal, Jenine, et al. 2020. “Have clusters of COVID-19 over time been described in condos, apartments and/or hotels? What are the most commonly hypothesized mechanisms of transmission?” Alberta Health Services, COVID-19 Scientific Advisory Group. July 16, 2020.