CDC investigators believe that most of the recent norovirus infections on cruise ships were spread person-to-person through hand-to-mouth activity. "We suspect that people are probably coming on board with the virus," says Dave Forney, chief of the 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."
Forney advises cruisers who are ill to avoid contact with other individuals and to report to the ship's medical facility. Unfortunately, many of them don't want to be told to stay in their cabins, adds Forney, so passengers spreading the virus around the ship are contributing to the ongoing problem.
Outbreaks on cruise ships have gained media attention, but an estimated 60 percent to 80 percent of all outbreaks of severe gastroenteritis occur on land, says the CDC. Norovirus infection is the most common cause of non-bacterial gastrointestinal illness in the United States; about 23 million cases of severe gastroenteritis a year are due to noroviruses. Noroviruses may be found in areas where people congregate together for days at a time, such as in schools, hotels, camps, nursing homes, and hospitals. Gastroenteritis is not a reportable illness in the United States except on cruise ships, so the public may be more aware of the shipboard incidences, says Forney.
By law, cruise ships that enter a U.S. port from a foreign port are required to report to the CDC, 24 hours prior to arrival, the number of passengers and crew on board who go to the ship's medical facility with gastrointestinal illness, even if the number is zero, says Forney. Having 3 percent or more of either passengers or crew reported with a gastrointestinal illness is considered an outbreak and cause for investigation.
Travelers shouldn't shun cruises, says Forney. "It is perfectly safe to go on cruise ships. The standard by which they are held for sanitation is the highest in the world." Extensive cleaning and disinfecting were carried out on ships immediately following reports of illness, Forney adds. And cruise lines continue to scrub and sanitize public areas of their ships, especially frequently touched surfaces such as handrails, elevator buttons, and even poker chips.