Federal health investigators say lab tests have confirmed that norovirus was to blame for an outbreak on a cruise ship that sickened nearly 700.

It was one of the largest norovirus outbreaks on a in 20 years.

The Royal Caribbean's Explorer of the Seas returned to New Jersey on Wednesday after cutting its 10-day Caribbean voyage short.

The U.S. Centers for Disease Control and Prevention has said 630 passengers and 54 crewmembers were sickened. The ship was carrying 3,050 passengers.

The CDC has not yet pinpointed a source for the norovirus. It can be picked up from an infected person, from contaminated food or water, or by touching contaminated surfaces.

The ship is due to set sail again Friday afternoon with heightened surveillance and steps to prevent a reoccurrence.

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