In Anyang, China, five members of a family came down with the coronavirus after hosting a guest from Wuhan in early January. But the visitor, a 20-year-old woman, never got sick herself.
Some individuals who are infected with the coronavirus can spread it even though they have no symptoms, studies have shown.
Asymptomatic carriers are a well-known phenomenon. But the coronavirus is a new pathogen, and these cases may complicate scientific efforts to detect cases and to curb transmission.