Passengers aboard the cruise ship Westerdam who have returned to the United States no longer need to isolate themselves and can resume normal activities, despite the fact that one passenger tested positive for the new coronavirus in Malaysia, the Centers for Disease Control and Prevention has advised.

A spokesman for the agency said on Saturday that the passenger’s diagnosis, confirmed twice by health officials in Malaysia, was a false-positive and noted that no other infections among passengers aboard the ship had been reported.

But on Sunday, the agency said that it had no direct evidence that the test result was a false-positive. Malaysian health officials announced that the passenger, an 83-year-old American woman, now tests negative for the infection, but experts say that is to be expected in a patient recovering from the illness.

(The test looks for an active infection; it is not an antibody test, which can tell whether a patient has ever been infected.)