Taking a Cruise? How to Stay Healthy on the High Seas

March 17, 2010— -- For the third cruise in a row, some of the passengers aboard Celebrity Mercury have fallen ill, apparently with the norovirus.

The ship departed Charleston, S.C., last week. Then 350 of the 1,829 passengers aboard became sick, a spokeswoman for the cruise line told The Associated Press.

The crew onboard is "conducting enhanced cleaning, to help prevent the spread of the illness" and will return to Charleston a day early to "conduct an extensive and thorough sanitizing onboard the ship and within the cruise terminal," Celebrity Cruises said in a statement.

More than 14 million people are expected to take a cruise in 2010, according to the Cruise Lines International Association. So how can you help prevent any illnesses on your next cruise?

ABC News senior health and medical editor Dr. Richard Besser stopped by "Good Morning America" to explain how to stay healthy on the high seas.

The Norovirus

The norovirus is highly contagious and its symptoms include nausea, vomiting, diarrhea, cramps and chills, Besser said.

The illness typically lasts 12 to 72 hours and usually occurs in places where people are in close quarters, such as schools, hospitals, nursing homes and cruise ships, according to Besser. It is the leading cause of foodborne outbreaks of diarrheal disease, accounting for more than 50 percent of these outbreaks.

It spreads through food, water, contaminated surfaces and person-to-person contact, Besser said. He added that the reason it could be so hard to get rid of on a cruise ship is because people can also bring it on board and it can live on surfaces for more than a week.

Cruise ships often visit places that have poor sanitation, so passengers can easily catch it from a restaurant they visited at a port, Besser explained.

Additionally, the infection dose of norovirus is very low, Besser said. It takes only 10 particles of the virus to make you stick, as opposed to the 100,000 particles of salmonella you would have to be exposed to in order to get sick.

Therefore, even if the crew does a very good job of cleaning the ship it only takes a little of the virus to get people sick again.