Study: Cruise Ship Diseases More Widespread Than Reported

(A. Kotok)

A study by scientists at the Centers for Disease Control and Prevention in Atlanta, Georgia suggests that outbreaks of communicable diseases on cruise ships may be more common than previously reported. The findings from an investigation of a norovirus outbreak on a cruise ship in January 2009 appear online in  the journal Clinical Infectious Diseases (paid subscription required).

Noroviruses are a group of viruses that can affect the stomach and intestines, and can cause gastroenteritis, an inflammation of the stomach and the large intestines. Common symptoms are vomiting, diarrhea, and some stomach cramping. The disease is highly transmissible through person-to-person contact and contaminated food, water, and environmental surfaces.

Passengers on the ill-fated cruise ship were given questionnaires about their health care behavior, hygiene practices, and possible norovirus exposures, with more than eight in 10 (83%) of the 1,842 passengers returning the forms. Some 236 passengers — about 15 percent — met the case definition for acute gastroenteritis. However, a large number of this group, 95 or 40 percent, did not report to the ship’s infirmary for care.

The highly transmissible nature of the norovirus seems to have helped spread the disease on the ship. The findings show that infected passengers were significantly more likely to have an ill cabin-mate and to have resided or dined on the deck level where a vomiting incident had occurred during boarding.

The most common symptom reported was diarrhea, followed by vomiting.  Stool samples from several ill passengers also tested positive for norovirus.

In contrast, crew members were much less likely to contract the disease; less than 1 percent of the crew reported illness. The authors point to possible causes for the lower infection rate among the crew: the few crew members who came in contact with the ill passengers, separate sleeping and eating quarters for the crew, and short-term immunity caused by exposure to previous outbreaks.

Because only 60 percent of the ill passengers reported their conditions to the infirmary, the study authors recommend adjustments in the reporting thresholds required for cruise lines. Lead author Mary Wikswo also recommends ill passengers be discouraged from boarding a cruise ship, and passengers who get ill on the cruise be encouraged to report their conditions as soon as possible.

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