A highly contagious virus sickened more than 100 passengers on a Holland America cruise ship that returned to San Diego Monday from a 10-day trip to Mexico.

Passengers on the Ryndam ship first showed signs of the norovirus six days into the trip, said Erik Elvejord, a spokesman for Holland America Line Inc. The virus causes nausea, vomiting and diarrhea and lasts 24 to 48 hours.

The virus sickened 104 passengers and six crew members, Elvejord said. The ship was carrying 1,226 passengers and 556 crew members. It visited several ports in Mexico's Sea of Cortez after leaving San Diego Feb. 15.

An 81-year-old woman who was suffering dehydration was hospitalized after the ship arrived in San Diego.

This is the fourth suspected norovirus outbreak on the Ryndam since early last year.

Holland America, based in Seattle, has not identified the source of the latest outbreak, Elvejord said. Typically, the virus is brought aboard by a passenger.

During the cruise, passengers were repeatedly reminded to wash their hands. Those who were infected were asked to stay in their rooms and compensated $100 a day.

The ship left San Diego late Monday afternoon on another 10-day cruise on Mexico's Pacific coast after a crew spent the day disinfecting passenger and crew areas, Elvejord said. Holland America told all 1,340 passengers that they could get a refund if they didn't want to board. Only one couple took the refund.