Indoor transmission of SARS-CoV-2.

It is essential to understand where and howsevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2)is transmitted.Case reports were extracted from the local Municipal Health Commissions of 320prefecturalmunicipalities in China (not including Hubei province). We identified alloutbreaks involving three or more cases and reviewed the major characteristics of the enclosed spaces in which the outbreakswere reported and their associated indoor environmental aspects.Three hundred and eighteen outbreaks with three or more cases were identified,comprising a total of 1245 confirmed cases in 120prefectural cities. Amongst the identified outbreaks, 53.8% involved three cases, 26.4%involved four cases, and only 1.6%involved ten or more cases. Home-based outbreakswere the dominant category (254 of 318 outbreaks;79.9%), followed by transport-based outbreaks (108;34.0%), and many outbreaks occurred in more than one categoryof venue. All identified outbreaksof three or more cases occurred in indoor environments, which confirmsthat sharing indoor spaceswith one or more infected persons isa major SARS-CoV-2 infection risk.