If you’ve ever dreamed of soaking in a private hot tub and gazing out on the open sea on the deck of a cruise ship, you might want to think twice. At least until you ask a few pointed questions about how that hot tub is maintained.
Earlier this year, CDC released a study that tracked a small but serious cluster of Legionnaires’ disease cases aboard cruise ships. Over an 18-month period, they documented 12 cases from just two ships. Ten people were hospitalized. Infections were caused by private hot tubs attached to staterooms, luxury perks that are supposed to help you relax and unwind, not send you to the ICU.
What Is Legionnaires’ Disease and How Do You Get It?
For those unfamiliar, Legionnaires’ disease is a severe form of pneumonia caused by inhaling mist or vapor that contains Legionella bacteria. The first known outbreak was in 1976 at an American Legion convention in Philadelphia—hence the name—and it was eventually traced to the air conditioning system of the hotel where the convention was held. Since then, we’ve learned that Legionella thrives in warm, wet environments where biofilms—those slimy layers of microbes—can form. Think cooling towers, showers, fountains… and, yes, hot tubs.
How Do Cruise Ship Hot Tubs Cause Legionnaires’ Disease?
The CDC investigation into these cruise ship cases revealed that the operating protocols for private hot tubs often don’t meet the same standards as those in public areas of the ship. They’re subject to less scrutiny, less frequent water replacement, and inconsistent disinfection practices.
Because the bacteria are hard to culture in standard lab tests, cases are often missed or misdiagnosed—unless a physician orders a urine antigen test for Legionella or a specialized culture.
Who Is Most at Risk for Legionnaires’ Disease?
What makes this particularly frustrating is that Legionnaires’ is preventable. We have very clear guidance on how to keep hot tubs safe: regular scrubbing to remove biofilms, testing for pH and disinfectant levels, filtering and replacing water on schedule. But if the people responsible for cleaning these tubs aren’t doing that work, then passengers, especially older adults or those with weakened immune systems, are at risk.
What Can You Do to Stay Safe on a Cruise?
I’ve led investigations of large Legionella outbreaks before, including one in New York City that sickened dozens of people from cooling towers. I’m also now making sure to remind friends and family to consider it on a cruise ship.
If you’re planning a cruise vacation, ask questions about how the tub is being maintained. You can even bring your own test strips if you want an extra layer of safety.