Cruise ship Explorer of the seas
© APSeptember 11, 2008: One of Royal Caribbean International's superliner cruise ships, Explorer of the Seas sits at Cape Liberty Cruise Port, the old Military Ocean Terminal in Bayonne, N.J.
The Centers for Disease Control and Prevention are investigating how more than 300 people have fallen ill on board a ship cruising the Caribbean.

The CDC said Saturday that health officials would board Royal Caribbean's Explorer of the Seas Sunday, when it is scheduled to dock at St. Thomas, U.S. Virgin Islands.

In all, 281 passengers and 22 crew members have reportedly fallen ill during the voyage, with most reporting vomiting and diarrhea. The CDC said it was not immediately clear what had caused the apparent outbreak. In response, the agency said that the ship's crew had stepped up its cleaning and disinfecting actions, encouraged passengers to report possible new cases, and prepared for new crew members to join the voyage midway through the journey.

The ship had departed Cape Liberty, New Jersey on January 21 for a scheduled 10-day cruise to the island of St. Maarten, which included scheduled stops in Haiti and Puerto Rico. There are a total of 3,050 passengers and 1,165 crew on board.

This marks the second gastrointestinal outbreak on a cruise ship stopping at US ports so far this year. An epidemiologist had to board a Norwegian Cruise Line ship in Miami on Jan. 19 after 130 passengers fell ill.

The last stricken Royal Caribbean ship was the Vision of the Seas, on board which 118 passengers fell ill last February, according to the CDC website.