Two patients have been diagnosed with the coronavirus in San Francisco, Mayor London Breed said Thursday.
They are the city's first cases in the global outbreak.
One patient is a man in his 90s. The other is a woman in her 40s. Neither has a travel history that could possibly explain how they came to be infected, city health officials said.
The elderly man is in serious condition in a hospital. The woman, hospitalized at a different, unnamed institution, is in fair condition.
Last week, Breed declared an emergency as the city anticipated that residents would be diagnosed with the virus.