The U.S. Centers for Disease Control and Prevention (CDC) today reported that a ship owned by Royal Caribbean Cruise Line ended a 10-day Caribbean cruise yesterday after 577 passengers and 49 crew members came down with gastrointestinal illness symptoms. The cause of the outbreak is yet to be determined, according to the CDC. Officials with Royal Caribbean said illness symptoms are consistent with norovirus, but company doctors are awaiting test results to confirm that diagnosis.

The Explorer of the Seas' voyage was scheduled for Jan. 21-31, but the trip was terminated Jan. 26 after an epidemiologist and an environmental health officer from the CDC's Vessel Sanitation Program (VSP) boarded the ship in St. Thomas (U.S. Virgin Islands) to conduct an epidemiologic investigation and evaluate the outbreak and response activities. Today's Investigation Update from the CDC noted that in response to the outbreak, Royal Caribbean Cruise Line and the crew aboard the ship took the following actions:

• Increasing cleaning and disinfection procedures according to their outbreak prevention and response plan,
• Making announcements to both notify onboard passengers of the outbreak and encourage case reporting,
• Collecting stool specimens from ill passengers and crew for submission to the CDC lab,
• Making multiple daily reports of gastrointestinal illness cases to the VSP,
• Preparing additional crew members to join the ship mid-voyage to assist with case management and intensified sanitation procedures,
• Consulting with CDC on plans for:
  1. Passenger notification procedures and the planned delayed embarkation schedule in Bayonne, NJ on Jan. 31, 2014,
  2. Disembarkation plans for active cases, terminal and transport infection control procedures.

Yesterday evening, Royal Caribbean issued the following statement to the media and the public:

Explorer of the Seas will return home from its 10-day cruise two days early, after an outbreak of gastrointestinal illness that spiked over the weekend. New reports of illness have decreased day-over-day, and many guests are again up and about. Nevertheless, the disruptions caused by the early wave of illness means that we were unable to deliver the vacation our guests were expecting. After consultation between our medical team and representatives of the [CDC], we think the right thing to do is to bring our guests home early, and use the extra time to sanitize the ship even more thoroughly. We are sorry for disappointing our guests, and we are taking several steps to compensate them for their inconvenience.

After returning to home port on Wednesday, Jan. 29, we will perform a thorough “barrier” sanitization program on the entire ship to make certain that any remaining traces of the illness are eliminated. It will be the third aggressive sanitizing procedure the ship has undertaken since we became aware of the issue, and will additionally provide a window of more than 24 hours where there are no persons aboard the ship, which is a significant help. 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.

At this point, it appears that reported illnesses among guests and crew peaked during the first few days of the cruise – though, as is common with many illnesses, some additional cases are to be expected over the course of the week. Our doctors tell us symptoms are consistent with that of norovirus, but that they are awaiting the results of tests to confirm that diagnosis. Our response included flying additional medical personnel and equipment to meet the ship, and conducting additional sanitizing procedures at two of the ship’s stops.