Passenger behaviors associated with norovirus infection on board a cruise ship--Alaska, May to June 2004.

Background: During May 2004, the Vessel Sanitation Program (VSP) investigated an outbreak of norovirus gastroenteritis on board a cruise ship sailing in Alaska waters. The objectives were to identify a common food item source and explore behavioral risk factors for person-to-person transmission among passengers.

Methods: A case was defined as three or more episodes of loose stools within 24 hours or two or fewer episodes of loose stools accompanied by one or more episodes of vomiting.