Broadcast reports said about 2,600 passengers were on the MS Oosterdam when the crew declared a "code red" after the first night of the cruise. Events were canceled and the boat returned to San Diego on Saturday after some passengers and several crew members got the norovirus, a stomach flu that made them sick with diarrhea, vomiting and other symptoms.
It wasn't immediately known what the source of the virus was.
The ship was sanitized and was expected to head back out to sea.