(CNN) -- The ill-fated Royal Caribbean cruise ship returns home Wednesday, but with an ignoble mark on it.
Nearly 700 crew and passengers fell ill aboard the Explorer of the Seas, the highest number of sick people reported on any cruise ship in two decades, CDC data show.
At least 629 passengers and 54 cruise workers got sick, but not all at the same time.
According to publicly-available data by the Centers for Disease Control and Prevention, that wins Explorer of the Seas the distinction of being the cruise ship with the highest number of sick people in 20 years.
The ship had 3,071 passengers and 1,165 crew members, according to the CDC.
Explorer of the Seas departed Cape Liberty on January 21 for what would have been a 10-day cruise.
Passengers and crew developed symptoms such as diarrhea and vomiting.
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CDC officials boarded the ship in St. Thomas on Sunday to study the outbreak and the response on the voyage back to Cape Liberty.
The cause of the illness was not clear, though the symptoms are consistent with norovirus, the cruise line said.
Noroviruses spread easily and are a common cause of gastroenteritis, which produces vomiting and diarrhea.
"The number of reported new cases of gastrointestinal illness has dropped sharply after a spike in the first days of the cruise, and most guests who fell ill are up and about," the cruise line said Monday.
"The drop in new cases is encouraging. However, it is not unusual in an outbreak to still have smaller, secondary spikes. That is why, after discussions with the U.S. Centers for Disease Control and Prevention and our medical team, we decided the most prudent course for the health of our guests and crew was to bring the cruise home on Wednesday, two days earlier than planned."
The company said all passengers would get a 50% refund and a 50% credit for a future cruise.
Those passengers who were ordered quarantined to their rooms will get an additional credit of one future cruise day for each day in confinement, it said.
"Guests scheduled for the next cruise on Explorer of the Seas can be confident that all possible measures will have been taken to prevent further problems," it added.
This ship is scheduled to return to its Cape Liberty, New Jersey, port on Wednesday for sanitizing to ensure there are no traces of illness, the liner said in a statement.
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