Cruise Ship Outbreaks of Gastroenteritis on Rise Since 2001

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Diarrheal Disease

Cases of diarrheal disease in passengers on cruise ships increased during 2001 through 2004, despite good results from environmental health sanitation inspection of the ships, a new study has found.

Researchers led by Elaine H. Cramer, M.D., analyzed cases of gastroenteritis reported on cruise ships calling on U.S. ports for a four-year period, in a study in the March issue of American Journal of Preventive Medicine.

The study showed that gastroenteritis outbreaks per 1,000 cruises increased overall from 0.65 in 2001 to 5.46 in 2004. However, ship environmental inspection scores were high during this period, with an average of 95 points on a 100-point scale

Noroviruses are the likely suspects, according to Cramer, medical epidemiologist with the Vessel Sanitation Program at the Centers for Disease Control and Prevention. "Since the introduction of more advanced laboratory techniques that can positively identify noroviruses, these viruses have increasingly been identified as associated with cruise ship outbreaks," Cramer said.

In the year before the study, two passengers were likely to come down with gastroenteritis on an average seven-day cruise, rising to three cases per cruise during the study period.

"We suspect that people are probably coming on board with the virus, " said Dave Forney, chief of CDC's Vessel Sanitation Program. "On a cruise ship, people are out and about in very public areas, and so we have this depositing of the virus on various surfaces that then would be easily picked up by others."

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"This increase (in outbreaks) highlights the inability of environmental programs to fully predict and prevent risk factors common to person-to-person and fomite spread of the disease," the researchers write.

Fomites are inanimate objects like, dishes, toilet seats or doorknobs that may be contaminated with infectious organisms and help spread disease.

Noroviruses are members of a group of viruses that affects the stomach and intestines, causing gastroenteritis, or inflammation of the gastrointestinal track. Symptoms include vomiting, diarrhea and stomach cramping that can last from 12 to 60 hours.

Noroviruses are spread by consuming food or liquids contaminated with the virus, touching contaminated objects or surfaces and putting hands near or in the mouth, or having direct contact with an infected person.

Passengers can take measures to prevent getting or spreading noroviruses, the most effective being hand-washing, Cramer said. "Passengers are well-advised to wash their hands whenever possible, especially because the cruise ship environment is a high-density, closed environment with soft fabrics and furnishings that can harbor viruses
for many days."

Cramer said that continued cooperation from cruise ship lines can help to curb gastroenteritis outbreaks. "The industry should continue to be vigilant for gastroenteritis among passengers and crew," she said, "and continue to publicize proper hand-washing techniques and encourage reporting of illness to the ship's medical staff."

Cramer also called on the industry to use cleaning chemicals known to be effective against norovirus and to work with public health agencies "to respond to higher-than-expected incidences of illness in a timely fashion."

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