(HealthDay News) -- Each year, nearly 9 million passengers embark from North American ports on cruise vacations.

Traveling on cruise ships exposes passengers to contained quarters and lots of other people. This means conditions may be ripe for transmission of germs, either from contaminated food or water, or more commonly through person-to- person contact.

The National Center for Environmental Health suggests these tips to help prevent the spread of illness:

• Wash your hands -- before and after eating or smoking; after touching your face or going to the bathroom, and when your hands are simply dirty.
• Leave the area if you see someone get sick (vomiting or diarrhea). Report the problem to cruise staff, if they haven't already been notified.
• Take care of yourself. Get plenty of rest and drink lots of water. Resting helps rebuild your immune system. Drinking water helps prevents dehydration.
• Be considerate of other people's health. If you're ill before taking a cruise, call the cruise line to determine if you can reschedule, and if there are alternatives to losing your deposit or fare.