This is the time of year when reports of cruise ships plagued by gastrointestinal illness begin to make the news, as vacationers take off in larger numbers on their spring and summer trips. Celebrity Cruises’ Infinity is the latest to grab the stomach-bug spotlight, with reports this week of 106 passengers falling ill; two weeks earlier, 114 cruisers were sickened on Royal Caribbean’s Legend of the Seas. (Celebrity and Royal Caribbean are subsidiaries of the same company, Royal Caribbean Limited RCL .)

If you’re getting the impression that these outbreaks are surprisingly common, you’re on to something. The U.S. Centers for Disease Control and Prevention (CDC) requires cruise ships to report outbreaks of gastrointestinal illnesses that affect 3% or more of the total number of passengers or crew onboard, so it’s easy to track which cruise lines are the biggest big-outbreak offenders. That title is shared between Celebrity Cruises and Princess Cruises, each of which had 15 gastroenteritis outbreaks affecting over 5,300 passengers from 2010 through mid-April this year.

Cruise Line Outbreaks, 2010-2015
Celebrity Cruises 15
Princess Cruises 15
Royal Caribbean 10
Holland America 10
Cunard Line 4

Princess and Celebrity are among the larger cruise lines, but they’re not the two biggest in terms of passengers carried: They trail market leaders Carnival and Royal Caribbean. Princess Cruises, owned by Carnival Corp. CCL , has a fleet of 18 ships that can hold a total of 71,716 guests at any one time. Celebrity Cruises has 11 ships with capacity for 25,030 passengers.

The CDC stats reflected above cover any type of shipboard gastroenteritis outbreak, regardless of what type of stomach bug it involves, but the most common outbreaks are of norovirus, a highly contagious virus that can be contracted by eating contaminated food or touching infected surfaces. It is the most common cause of acute gastrointestinal problems in the U.S. and causes between 19 million and 21 million illnesses a year (most of them on land, of course), resulting in between 570 and 800 deaths a year.

But while cruise line outbreaks tend to grab headlines and air time, the reality is that the odds of getting a stomach bug on your cruise vacation are quite low. For example, more than 20 million people traveled on one of Cruise Lines International Association’s 400-plus ships in 2013. That year, 1,409 passengers got sick in nine ship-wide outbreaks reported to the CDC–that’s about 0.007% of all cruisers, or one out of every 14,000 or so who sailed that year. Even if you count people who got sick outside of these bigger outbreaks, the likelihood of getting ill is still lower than the news coverage would suggest. By way of comparison, a high school basketball player has a far higher chance (0.03%) of eventually being drafted into the NBA, according to the National Association of Sports and Physical Education.

The CDC has strict sanitation standards for cruise ships under its Vessel Sanitation Program, which helps ensure that each boat is doing as much as it can to protect passengers. The agency inspects ships twice a year and assigns a score to each, ranging from 0 to 100. Any score below 85 is considered failing, and the CDC can recommend that the ship not sail if there is an imminent public health risk. (Want to check the score on a specific line or ship? The CDC publicizes that data here.)

The vomit-centric headlines don’t seem to be hurting cruise lines in general. The cruise industry posted worldwide revenues of $37.1 billion last year, up 38.2% from 2010, according to Cruise Market Watch. Global revenues are forecast to hit $39.6 billion this year.

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