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With the latest report of a stomach bug sickening more than 600 people on a Royal Caribbean cruise ship, we took a look at similar recent outbreaks on cruises and found more than a dozen in just the last five years.

While the ill passengers aboard the Royal Caribbean ship haven’t been officially diagnosed yet, according to the Centers for Disease Control (CDC), the 577 passengers and 49 crew members who are sick to their stomachs, vomiting and experiencing diarrhea are likely infected with norovirus. The virus affects the stomach and intestines and can be ingested from contaminated food or water; contact with an infected person can also spread the infection (and that carrier may not even know he is spreading the disease, since it can take up to two weeks for symptoms to appear). Once they do, they aren’t pretty. And the virus can spread quickly, especially in small, contained spaces like a cruise ship.

In some cases, it can spread through unsanitary bathroom practices, since the microbe resides in the feces. But the CDC says it’s nearly impossible to determine if outbreaks were caused by infected people who board a ship, or by contaminated food or water. The agency has a task force called the Vessel Sanitation Program that requires any ship visiting foreign ports and carrying more than 13 passengers to submit to two random sanitation inspections per year. When outbreaks occur, the CDC responds, sending a scientist on board to take samples for testing and to monitor sanitation procedures.

So have these VSP experts come up with any best practices to protect future cruise ship passengers from unpleasant experiences? It’s probably a good idea to avoid raw and uncooked shellfish, or any other food and water that doesn’t smell fresh or shows signs of being possibly contaminated. Washing your hands — a lot — and staying clear of public surfaces like toilets and door handles could also help.

And if you’re still considering a cruise in the coming months and wondering how likely it is that you will run into norovirus, we thought you should be armed with the latest on the most recent outbreaks, listed from worst to…still a serious vacation downer.

1. Royal Caribbean Cruise Line, Explorer of the Seas

Current number sick (including both passengers and crew members): 626

The ship is currently on its way to dock in New Jersey. CDC members are on board to monitor the cases and advise the cruise line on its response. The CEO of Royal Caribbean Cruises Ltd. told NBC News that the company screens its passengers for visible signs of illness as best they can and that their personnel has reacted as quickly as possible to the problem.

2. Celebrity Cruises, Mercury (February 2010)

Total number sick: 443

“I never had anything like this,” Kenneth Thompson a 71-year-old from Concord, S.C. told NBC News about his vomiting symptoms on the cruise. “It just came out of me in streams, just gushes of it.”

3. Celebrity Cruises, Mercury (March 2010)

Total number sick: 419

A second Celebrity Cruise ship is harbors norovirus, one month later, raising concerns about the line’s sanitation practices.

4. Princess Cruises, Crown Princess (January 2010)

Total number sick: 396

In 2010, there were 14 outbreaks of illnesses on ships , including this one. Eight were attributed to norovirus.

5. Princess Cruises, Crown Princess (February 2012)

Total number sick: 363

The cruise, which embarked just a month after another outbreak on the ship, returned to Ft. Lauderdale two days early as passengers started falling ill.

6. Celebrity Cruise Lines, Celebrity Summit (September 2013)

Total number sick: 335

Many of the infected experienced severe stomach pains along with vomiting and diarrhea and were confined to their cabins to prevent spread of the virus. In 2013, the CDC reports that there were nine cases of widespread illness on cruises, and seven were caused by norovirus.

7. Fred Olsen Cruise Lines, Balmoral (January 2010)

Total number sick: 310

The world cruise started in Dover, England and after visiting several countries, was supposed to finish the trip in Los Angeles, California. Fifteen days before reaching L.A., the first of the 293 passengers and 17 crew who were infected started getting sick.

8. Princess Cruises, Ruby Princess (March 2013)

Total number sick: 276

The cruise returned from what was a week long trip in the Eastern Caribbean to Fort Lauderdale, Fla. New passengers scheduled on the next cruise were not allowed on the ship until the CDC finished a required sanitation assessment.

9. Princess Cruises, Coral Princess (February 2009)

Number sick: 271

This cruise also had the distinction of sickening passengers with E. coli as well as norovirus.

10. Carnival Cruise Line, Carnival Liberty (April 2009)

Total number sick: 265

The ship was cleaned and disinfected when it pulled into Miami, causing a delay for the next set of passengers.

11. Royal Caribbean Cruise Line, Voyager of the Seas (January 2012)

Total number sick: 259

Several sick tourists were quarantined while the ship was delayed at various ports to sanitize.

12. Cunard Line, Queen Mary 2 (December 2012)

Total number sick: 220

All the tables and seating on this trip had to be sanitized and disinfected before the crew served the buffet meals, and crew members reported any cases of gastrointestinal illness to the CDC twice a day.

13. Princess Cruises, Sun Princess (July 2012)

Total number sick: 216

As with the other major outbreaks, two CDC VSP members boarded the ship to conduct health assessments and gauge how the situation was being contained. Many passengers on the ship provided stool samples for testing, which helped to verify norovirus as the cause.