Norwalk virus was the source of an outbreak that sickened about 225 passengers aboard the Norwegian Cruise Lines ship Pride of Hawai'i, state health officials confirmed yesterday.

The ship returned to Honolulu yesterday morning after completing its seven-day, round-the-Islands cruise, which began Nov. 5. The ship left Pier 1 at Honolulu Harbor last night on another seven-day cruise.

The federal Food and Drug Administration is leading the investigation of the outbreak, but the state Health Department conducted tests to determine the type of virus at its laboratory, said state spokeswoman Janice Okubo. "We did report those results: Norwalk virus."

No passengers were hospitalized as a result of the outbreak.

In a statement from the company, officials said the ship "has been carrying out an extensive range of preventative measures on board and does not expect this issue to carry forward into the next cruise."

Passengers boarding yesterday were told before boarding that a number of passengers on the previous cruise experienced symptoms of stomach flu, so the incoming passengers could decide whether to sail or to receive credit on a future cruise.

FDA officials were aboard the ship yesterday to review the vessel's guidelines while cleaning was being done. NCL officials said the FDA approved all policies and procedures and verified that everything was in place and the vessel could continue its regular operations.

Reports of the gastrointestinal illness surfaced last week as the ship was touring the Neighbor Islands. Norwegian Cruise Lines said the virus, also called norovirus, affected about 9 percent of the ship's 2,500 passengers.

They were given the option not to cruise, and if they chose not to, they received credit for a future cruise. A company statement indicated that passengers who felt ill — suffering from nausea, vomiting and diarrhea — and their cabinmates had been asked to remain in their cabins for 24 hours and were given free medical treatment and a $200 on-ship credit.

SPECIAL TREATMENT

Cruise officials said that while passengers were confined to their cabins, they were given whatever food service they liked, including from the specialty restaurants, at no charge. If they chose not to stay in their cabins, they were asked to disembark at the next appropriate port of call, from which NCL flew them home and provided a pro-rated credit for a future cruise.

The federal Centers for Disease Control and Prevention estimates that 23 million cases a year of acute gastroenteritis are due to norovirus infection. It has an incubation period of 12 to 48 hours, and the illness generally runs its course in about 24 to 48 hours.

The Honolulu office of the FDA did not immediately return calls yesterday, which was a federal holiday.

Okubo said in cases like this that involve more than 2 percent of passengers becoming ill, a ship is required to report to the FDA. "We don't have any jurisdiction over cruise ships," she said.

18 OUTBREAKS IN 2007

The Centers for Disease Control and Prevention tracks shipboard illnesses when 3 percent or more of those aboard report sickness. The center's Web site said there have been 18 shipboard outbreaks this year. Norovirus outbreaks often occur in group settings such as cruise ships and dormitories, and in institutional settings such as schools, childcare facilities and nursing homes.

The centers said people can reduce their chances of getting infected by frequent handwashing, prompt disinfection of contaminated surfaces with household chlorine bleach-based cleaners and prompt washing of soiled articles of clothing.

Reach Robbie Dingeman at rdingeman@honoluluadvertiser.com.