Airline passengers wearing face masks walk out of the international terminal at the San Francisco International Airport on Jan. 31. Photo: Yichuan Cao/NurPhoto via Getty Images
Why it matters: COVID-19 infections have spread from China to some 40 countries and territories. There are 57 cases in the U.S. The CDC anticipates it will spread further, and that's why Breed said she took the action. While there have been no confirmed cases among San Francisco residents, three people have been treated for the virus in hospitals in the city, the Los Angeles Times notes.