A new strain of stomach bug was the virus responsible for almost 700 recent illnesses on a Caribbean cruise ship.
The Centers for Disease Control and Prevention on Thursday said by the new Sydney strain of norovirus was the cause of the illnesses on board Royal Caribbean's Explorer of the Seas.
The ship, carrying 3,050 passengers, docked in New Jersey last week after 630 passengers and 54 crew members grew ill during a Caribbean cruise.
It was one of the largest norovirus outbreaks on a cruise ship in the last 20 years.
The Sydney strain emerged within about the last two years.
It's not considered unusually dangerous, but has quickly become a common cause of cases of vomiting and diarrhea that last a few days.