Health officials in California, Oregon and Washington reported three new cases of coronavirus with no travel history to China or known exposure to carriers, including one involving a high-school student, adding to concerns that the virus is spreading in American communities.

Late Friday, Washington health officials said a high-school student in Snohomish County came down with a fever, body aches and a headache on Monday and sought treatment at local clinics. He returned to school Friday morning after feeling better but was...