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A Royal Caribbean cruise ship is headed back to New Jersey two days early after an outbreak of gastrointestinal illness spiked over the weekend, the cruise line says.

A report posted online by the Centers for Disease Control and Prevention says 577 of the ship's 3,050 passengers, or 18.9%, and 49 of 1,165 crew, or 4.2%, reported symptoms such as vomiting and diarrhea during the voyage.

The cruise line announced the change in itinerary Sunday after inviting U.S. health inspectors to investigate and evaluate conditions on its Explorer of the Seas cruise ship during a port call in the U.S. Virgin Islands.

The ship launched Jan. 21 from Cape Liberty, N.J., and was scheduled to return Friday. Royal Caribbean says Explorer of the Seas instead will return to Cape Liberty on Wednesday.

Earlier this month, the CDC reported a similar outbreak on a Norwegian Cruise Line ship. Last year, it reported nine cases, including one involving a Royal Caribbean ship.

In most cases, the cause was found to be norovirus, a gastrointestinal illness that spreads swiftly when large groups of people are contained in a small area such as dormitories, nursing homes and cruise ships.

Royal Caribbean said Sunday that reports of illness peaked during the first few days of the cruise. It said cleaning products and disinfectants proven to kill norovirus were being used to clean the ship before it returned to the USA. It said a full sanitization program would be carried out after the Explorer of the Seas reached its home port.

Janet Diaz, a company spokeswoman, said the ship underwent "extensive and thorough sanitizing" during its previous port call in Puerto Rico to help prevent more people from getting sick.

"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," Royal Caribbean Cruises said in a statement.

Passengers and crew who fell ill have "responded well to over-the-counter medication being administered on board the ship," Diaz said.

On Friday, an Explorer of the Seas passenger named Arnee Dodd tweeted that she had fallen ill aboard the ship and was quarantined with other sick people. The Connecticut woman wrote that ship employees "put a lockdown on food & are constantly cleaning everything."

Royal Caribbean said it was "taking several steps" to compensate passengers for the shortened trip. It also sought to assure customers scheduled for the ship's next voyage that "all possible measures will have been taken to prevent further problems."

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