One of the biggest misconceptions about cruise ships is that they’re germ incubators—that you can't escape. 

But the likelihood of catching a stomach bug on a seven-day voyage is less than 1 percent—which is about a third the risk of getting infected in your day-to-day life back home, says Dr. Carter Hill, a Seattle-area emergency-room physician who specializes in cruise-ship medicine. Here's the catch: If someone onboard does succumb to a nasty virus, it can spread quickly across the ship because it's a closed environment where many people share many things. When a sick passenger with poor hygiene touches a water pitcher, doorknob, or poker chips, other passengers may fall ill, too. 

To avoid the flu virus, stomach bug, or any other infectious condition, stick with the following strategies: