A highly contagious virus that causes stomach flu sickened about 220 passengers aboard a Norwegian Cruise Lines ship that returned Monday to Honolulu after its weekly seven-day cruise around the islands, officials said. Lab tests confirmed a norovirus - which causes nausea, vomiting and diarrhea - aboard the Pride of Hawaii, said Janice Okubo, spokeswoman for the Hawaii Department of Health. "It's one of the common viruses we've been seeing on cruise lines," Okubo said. "Most of the time, people recover."

The Norwalk-like virus infected about 9 percent of the ship's 2,500 passengers, NCL said. Virus symptoms typically last a day.

Passengers who felt sick, as well as their cabinmates, were asked to remain in their rooms for 24 hours. Norwegian said it was giving those passengers a $200 on-ship credit.

The company said in a statement that the ship "has been carrying out an extensive range of preventive measures on board and does not expect this issue to carry forward into the next cruise."

Cruise lines usually rigorously clean ship surfaces, Okubo said.

The U.S. Food and Drug Administration is investigating, Okubo said.

Norwegian describes Pride of Hawaii as the largest and most expensive U.S.-flagged cruise ship ever built. It began service last year.

Norwegian was acquired in February 2000 by Star Cruises PLC of Malaysia, according to the cruise line's Web site.