(3:10 p.m. EST) -- At least 10 percent of passengers on Holland America's Amsterdam have been struck with a stomach bug, the Centers for Disease Control and Prevention reported. Of some 791 passengers onboard, 81 were sickened.
Holland America confirmed the outbreak to Cruise Critic.
"During the 25-day November 11, 2012 Sydney, Australia, to San Diego sailing on ms Amsterdam, a number of guests reported to the infirmary with a common type of gastrointestinal illness," said Holland America spokeswoman Sally Andrews. Cruise lines participating in the CDC's Vessel Sanitation Program -- and every major operator does -- are required to report the number of GI cases evaluated by medical staff, before arriving at a U.S. port. A separate notification is required when the count exceeds 2 percent of the total passengers or crew onboard.
The majority of sick passengers reported the onset of symptoms in the past week, after the ship left its last port of call, Hilo, Hawaii, on November 29.
A small number of crew (0.98 percent) also reported symptoms, the CDC said.
In response to the outbreak, Amsterdam's crew increased cleaning and disinfection procedures, notified passengers onboard and encouraged extra hand washing, added the CDC.
Additionally, Jeff Farschman, a passenger on Amsterdam, blogged that the crew moved the buffet extravaganza to the Lido behind glass and canceled the Fall Ball, an autumn themed dining and dance event, to prevent the further spread of the illness.
The 25-night sailing concluded today (Dec. 5) in San Diego, where it will undergo an intensive cleansing and inspection by two CDC Vessel Sanitation Program environmental health officers.
Embarkation for today's 17-night Panama Canal cruise to Fort Lauderdalehas been delayed until 2 p.m. PST.
Norovirus is the second most common illness next to the common cold and is highly contagious, spreading easily in confined spaces like hospitals, hotels, dormitories and cruise ships. Symptoms include vomiting and diarrhea, and millions are infected each year.
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--by Dori Saltzman, News Editor