Health officials have identified what could be the first U.S. case of the novel coronavirus spreading within the general population. But a hospital says the diagnosis was delayed for days. Here, a passenger wears a face mask on a train in San Francisco on Wednesday.

Health officials have identified what could be the first U.S. case of the novel coronavirus spreading within the general population. But a hospital says the diagnosis was delayed for days. Here, a passenger wears a face mask on a train in San Francisco on Wednesday.