Read Caption

The Explorer of the Seas is docked in St. Thomas, U.S. Virgin Islands, on January 26.


Cruise Ship Illness: Why Are Ships So Prone to Norovirus Outbreaks?

Nearly 600 people sickened on Caribbean cruise likely have norovirus.

For nearly 600 people sickened during a Royal Caribbean International cruise to the Caribbean, their vacation has been no day at the beach.

About a fifth of the 3,050 people aboard Explorer of the Seas, which left Cape Liberty, New Jersey, on January 21 for a ten-day cruise, have come down with a gastrointestinal illness. Due to the outbreak, the ship will cut the cruise two days short and return to New Jersey on Wednesday, according to news reports.

Gastrointestinal outbreaks are relatively common on cruise ships. According to data from the U.S. Centers for Disease Control and Prevention (CDC), there were 14 gastrointestinal outbreaks on cruise ships in 2010 and 2011, 16 in 2012, and 9 in 2013.

Though the number of news reports on cruise ship illnesses could make it seem like such outbreaks are on the rise, they're not any more prevalent than in the 1990s and 2000s.

Instead, "People are more aware of it because of the media and better diagnostic techniques," says Michael Zimring, director of the Center for Wilderness and Travel Medicine at Mercy Medical Center in Baltimore, Maryland.

Adds John R. Palisano, a microbiologist at Sewanee: The University of the South in Tennessee, by email: "It makes the news during these cruises because there are a great number of people who are in confined space and very susceptible to infection because it is so easily spread."

In the case of the Royal Caribbean outbreak, the CDC is testing specimens taken from sick people onboard the ship and lists the cause of the outbreak as unknown.

Norovirus Likely Culprit

The symptoms seem to suggest norovirus, a highly contagious condition that has been responsible for gastrointestinal cruise ship outbreaks in the past.

Gastrointestinal illness is an inflammation of the stomach and large intestines that may cause vomiting, watery diarrhea, fever, nausea, stomach cramps, and more, according to the CDC. The causes can be viral, bacterial, or parasitic. (Explore a human-body interactive.)

Norovirus is the most common cause of gastroenteritis in the U.S., with between 19 to 21 million cases a year and more than 56,00 hospitalizations.

Once an infected person gets onboard a ship, the virus can be spread quickly, mainly through hand contact with ship railings, bathroom doors, and especially buffet food, said Zimring. (Read blog post: "An Infinity of Viruses.")

The industrial-size servings of food on a cruise ship with hundreds of passengers can be particularly worrisome, since once the virus enters the food it can spread rapidly. Food can also get more easily contaminated with the virus if it sits out for several hours, as is often the case with buffet-style meals.

And so many people being in one place eases the virus's spread. "In close quarters it doesn't get away, everything's concentrated," Zimring says.

There are steps that cruise ships can take to prevent outbreaks. Some ships will sanitize railings, handles, and other commonly touched objects with alcohol washes to kill the viruses. (See pictures of viruses.)

The CDC, which runs a Vessel Sanitation Program, reported on its website that Royal Caribbean has taken steps to contain the outbreak, including cleaning and disinfecting the ship, collecting stool specimens from ill passengers to send to the CDC laboratories, notifying passengers daily about the outbreak, encouraging them to report cases, and more.

Good Hygiene Is Key

The best defense against gastrointestinal disease, Zimring says, is to wash and sanitize your hands constantly, and avoid touching anything that others might have, especially bathroom doors and railings. (Use a towel if you need to touch those objects, Zimring advises.) (Also see "Washing Hands in Hot Water Wastes Energy, Study Says.")

In terms of eating, Zimring said to avoid buffet meals entirely, if you can, or if not, try to be the first person there at the buffet, when the food is still freshly prepared and no one has eaten yet. (Also see the CDC's advice for healthy cruising.)

Another crucial but easily forgettable piece of advice: Don't eat tepid food. If it's supposed to be hot, eat it when it's hot; the same goes for cold food. Tepid food is a signal that it's been out for a while and may have become contaminated.

Lastly, use plastic cups instead of real drinking glasses in your hotel room, drink lots of water, and get plenty of sleep.

Zimring also suggests considering smaller cruises, which tend not to have as many disease outbreaks.

Follow Christine Dell'Amore on Twitter and Google+.