It's mid-winter, and that means it's prime time for the nasty gastrointestinal bug called norovirus to invade cruise ships and ruin vacations. The first big outbreak of the season came earlier this week when Royal Caribbean International's Explorer of the Seas reported to the Centers of Disease Control that roughly 20 percent of its passengers and crew had contracted the illness. That's a big number. These outbreaks typically stay below 5 percent of the ship's population, and a virus that affects 2 percent or more must by law be reported to the CDC.

The 14-year-old, Cape Liberty, N.J.-based ship was on a 10-day Eastern Caribbean cruise, and cruise line officials decided to cut short the sailing by two days and return the ship to its home port. For anyone on board, it's a vacation nightmare, though particularly for those who caught the bug – being stuck in your cabin, sick for days when all you want to do is enjoy the warm Caribbean weather.

The CDC offers one big tip for avoiding norovirus: Wash your hands often, and always before and after eating. But below, we used our past experience on cruise ships to come up with a few more things to do in order to avoid becoming ill, even if everyone on your ship appears healthy:

1. Avoid the buffet. It's not the food that's necessarily the problem, though. The culprits often are the contaminated utensils everyone is using to scoop up their salads, fresh fruits, desserts, and all of the other goodies on offer. Once you've touched a contaminated utensil, that bread you're about to eat with the same hand also becomes contaminated.

2. Steer clear of raw shellfish; if the crew member who prepared it is under the weather, it's likely you will be, too.

3. Use only your cabin bathroom rather than the ship's public restrooms. And if you pop into a public restroom to check your hair in the mirror, keep your hands off the counters.

4. Keep your hands off indoor stairway banisters and outdoor rails.

5. Avoid elevators whenever possible; use the stairs instead.

6. Enjoy the ship's fitness room, but douse your hands with sanitizer before and wash your hands thoroughly afterward.

7. If ship staff is handing out sanitizer at the entrances to dining venues, gladly take some and use it.

8. If you order a soda or a glass of water from a ship's bar, use a straw.

9. Keep your distance from anyone who appears to be under the weather. If you are onboard a ship where a breakout occurs, stay in your cabin and let the ship's medical staff help you.

10. And finally, drink plenty of fluids! Not only will it help you avoid dehydration. It will also give your body a better chance at fighting whatever bug might be going around.

The presence of norovirus on a cruise ship almost invariably makes headlines in the national media. One reason is because passengers are so connected these days, and word of an outbreak spreads by phone and email almost as fast as the virus does. But, in fact, norovirus is much more common in places like long-term care facilities, hospitals, schools, dormitories, and other places where a lot of people are living in a contained space.

According to CDC records, onboard illness happens between 10 and 15 times per year, and in most cases, a few hundred passengers are affected each time. That might seem daunting, but remember that 15 million people worldwide will take a cruise this year; the vast majority of them will not get sick.