One woman aboard the Explorers of the Sea yelled, "We made it!" as the ship docked Wednesday. Other passengers, with blankets wrapped around them, stood on deck to watch the ship pull in.
Bill Rakowicz, of St. Thomas, Ont., one of 300 Canadians aboard the ship, said at first he thought he was just seasick. Then he said he left his room and saw people with gloves and "people sick everywhere."
The 61-year-old said he suffered from vomiting, pain and diarrhea and that his experience was simply "awful." However, he gave high marks to the Royal Caribbean cruise line for going "above and beyond" in its response.
The U.S. Centers for Disease Control and Prevention said its latest count puts the number of those sickened at 630 passengers and 54 crew members. The ship was carrying 3,050 passengers.
Health investigators suspect norovirus, but lab results are not expected until later this week.
If norovirus is to blame, it would be one of the largest outbreaks in last 20 years, the CDC said. A 2006 norovirus outbreak on a Carnival Cruise Lines ship also sickened close to 700.
Norovirus — once known as Norwalk virus — is highly contagious. It can be picked up from an infected person, contaminated food or water or by touching contaminated surfaces. Sometimes mistaken for the stomach flu, the virus causes bouts of vomiting and diarrhea for a few days.
The CDC said it recommended to cruise operator Royal Caribbean that people who still have symptoms be housed in nearby hotels or seen at medical facilities before travelling home.
CDC investigators boarded the ship during its U.S. Virgin Islands Port call on Sunday. They said no single food or water source or other origin has been identified.
Explorer of the Seas is on track to depart at its originally scheduled time Friday afternoon on its next cruise, a 9-night trip with port calls in Puerto Rico, St. Thomas, the Dominican Republic and Haiti, a Royal Caribbean spokeswoman said.