Disease on Cruise Ship Identified : Health: 600 passengers and crew of Viking Serenade were stricken with shigellosis, a virulent intestinal ailment. The source has not been determined.

More than 600 passengers and crew members who fell ill aboard a Royal Caribbean cruise ship last week were stricken by shigellosis, a virulent intestinal disease, investigators from the Centers for Disease Control and Prevention said Monday.

The source of the shigella bacteria aboard the San Pedro-based Viking Serenade had not yet been determined, and CDC investigators were sampling the ship’s food and water and testing its food preparers for signs of infection.

The cruise liner returned to port from Ensenada, Mexico, on Thursday, a day early from what was supposed to be a four-night journey, after large numbers of passengers fell ill with severe bouts of vomiting, fever and diarrhea.

Of the passengers aboard, 583, or 37% of the total, reported signs of the illness, while 40 crew members out of 612 were also stricken, according to the CDC. The bacteria was found in half the stool samples taken from the passengers.

“It is a nasty bug. Any disease that causes fever, diarrhea, cramps and vomiting is extremely uncomfortable, and particularly the very old and the very young are especially impacted,” said CDC spokesman Bob Howard in Atlanta. “For 37% of a group to be made ill, we certainly have to classify this as a large outbreak.”

Six people aboard the ship were hospitalized, including one 78-year-old man, Clarence Bazar of Long Beach, who died--apparently of a heart attack--after he fell ill with the intestinal symptoms and was hospitalized in Ensenada. Bazar was seriously ill before the cruise with heart disease, diabetes and cancer.

Howard said investigators have not yet determined whether the disease contributed to Bazar’s death.

Shigellosis spreads through contact with feces, usually via food or person to person, although it can also be transmitted through the water supply. Just a small number of the organisms--10 to 200--are enough to make a person violently ill, and Howard said one infected food handler could spread the bug to hundreds of people aboard the ship without even knowing he or she had the disease.

At the request of the CDC, the cruise line is testing all food handlers, surveying the water system and removing all prepared food from the ship. CDC investigators said Royal Caribbean Cruise Lines, which is sanitizing and inspecting the vessel, is acting “expeditiously.”

The cruise ship, according to Howard, received “an excellent score” in a sanitary inspection conducted by the CDC earlier this year.

“You can have a vessel that is absolutely spotless and all it takes is one infected food source or one infected handler who may or may not know he or she is infected,” Howard said. “A lot of it has to do with a large number of people in a confined area. The bottom line is we simply don’t know the mode of transmission in this case. We continue to do testing on water, stool samples and blood samples.”

Royal Caribbean’s chairman, Richard Fain, said the company is cooperating with the CDC to ensure that the bacteria is eradicated before the ship’s next scheduled voyage Friday.

The Viking Serenade left San Pedro on Aug. 29, and the first reports of illness occurred the next day, while it was docked off Santa Catalina Island. The number of ill grew steadily as the ship cruised toward Baja California.

With an incubation period of 12 hours to five days, shigellosis typically begins with fever, stomach pain and diarrhea, which often turns bloody after a day or so, and can last a week.

The type of shigella found in the passengers-- Shigella flexneri-- can be successfully treated with antibiotics.

It is spread through physical contact or in food by an infected person who fails to wash his or her hands. Some people can be infected with the bacteria and pass it on to others without experiencing any symptoms; the infection can even be transmitted to others up to four weeks after the illness ends.

In some cases, such as with a recent waterborne illness in Milwaukee, bacteria can cause outbreaks of intestinal disease that afflict hundreds of thousands of people. Shigellosis strikes about 15,000 people a year, Howard said.

The Miami-based Royal Caribbean Cruise Lines promised full refunds to the passengers. Fares for the excursion ranged from $599 to $1,899 a person including air fare.