This germy spot will make you need the bad kind of R&R—rest and recuperation
This Is the Dirtiest Part of a Cruise Ship, According to the CDC
Published on May 22, 2025
Setting sail sounds idyllic … in theory. But lately, you hear the word cruise and you can almost hear the Jaws soundtrack playing in anticipation of some awful illness making its way toward you. We usually hear about norovirus outbreaks on cruise ships, but now there’s an even bigger health threat on board—and it’s circling a surprising spot. In fact, the CDC just traced two major bacterial-illness outbreaks to it and is warning passengers about its hidden dangers.
So what is this infection hot zone and just how sick can it make you? Reader’s Digest reached out to microbiologist Jason Tetro, aka The Germ Guy and author of The Germ Code, to find out. Read on to get the dirt on the nasty bugs passengers are catching from cruises—and how you can sidestep a trip to the ship’s sick bay.
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What is the dirtiest part of a cruise ship?
Believe it or not, it’s not the restrooms or those buffet tongs. It’s the hot tubs—specifically private hot tubs in the ship’s luxury suites. That’s right: You could be paying a whole lot of money to get really sick.
The problem with these personal hot tubs? They’re usually not cleaned enough. Hot tubs “for private use tend to be less regulated or unregulated and may not undergo the same level of testing or disinfection as the public ones,” Tetro says.
And when they’re not properly maintained, hot tubs are “in essence, a three-dimensional petri dish,” he adds. “All bacteria need three things: a nice warm place to grow, plenty of water, and organic material they can use for food.” A big ol’ steamy tub of barely cleaned water? Check, check and check!
While a ship’s public hot tubs can also harbor dangerous bacteria, they are less risky since they’re cleaned more frequently, according to a 2024 report from the CDC.
What diseases can you contract here?
The CDC traced two outbreaks of Legionnaires’ Disease, a life-threatening type of pneumonia caused by legionella bacteria, to hot tubs on cruise shots. In that same 2024 report, the CDC warned that “hot tubs offer favorable conditions for Legionella growth and transmission when maintained and operated inadequately.”
But that’s not the only serious illness you can pick up here. According to Tetro, pretty much any bacterial pathogen can be found in these tubs. “Over the years, researchers have looked for different species and found several that can lead to gastrointestinal disease, ear infections, skin infections and respiratory infections,” he says.
A cruise-ship hot tub can also give you a nasty bacterial skin infection, according to a report in the journal Microbiology Spectrum. You could pick up MRSA (officially called methicillin-resistant Staphylococcus aureus) or Pseudomonas aeruginosa, which can cause skin, blood and lung infections.
How big of a problem is this?
A pretty big problem! Cruise hot tubs pose a major public-health problem. In the two episodes reported by the CDC, 12 passengers got sick, and 10 of them ended up hospitalized. Legionnaires’ disease can lead to organ failure, septic shock and death. It’s particularly risky for older and immune-compromised people.
How will you know if you’ve been in an infected hot tub?
You’ll start feeling very ill. Early symptoms of Legionnaires’ disease hit two to 10 days after exposure to the bacteria. They include headache, muscle aches and a high fever. A day or two later, you could develop lung symptoms like shortness of breath, chest pain and a productive cough with mucus and/or blood. You may also experience other symptoms like vomiting, diarrhea and/or mental changes.
If you feel unwell on a ship or after disembarking, see a doctor immediately. Legionnaires’ disease requires antibiotics. The sooner you treat it, the more likely you are to avoid life-threatening complications.
Does this mean you should avoid hot tubs on cruises?
Private hot tubs on cruises are risky, for sure, so you may want to avoid this avoidable cruise mistake. But you don’t have to automatically swear off the public hot tubs—as long as you take some steps to protect yourself, Tetro says.
Before you even book your trip, you can check safety inspection ratings through the CDC’s website.
But don’t stop there: The CDC encourages cruise passengers to do their own safety checks using hot-tub test strips, which you can get at Amazon, Lowe’s or Home Depot for around $10. For a hot tub to be safe, the chlorine level should be at least 3 parts per million; if the reading is above 10 ppm, that’s a red flag. The level of bromine should be 4 ppm to 8 ppm. If the reading is above 8 ppm, that’s risky. Alert the hot tub operator.
The CDC also shares questions to ask the cruise ship operator before taking a dip. They include:
- Are chlorine and bromine levels and pH checked at least twice a day?
- What are the latest inspection results for this hot tub?
If the ship is following proper safety protocols, they’ll be happy to answer these questions. “If they are sketchy and not open about it, maybe take a pass,” Tetro says.
And even if the hot tub seems safe, he adds, “be sure to have a nice shower to make sure that any potential pathogenic hitchhikers end up in the drain.”
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Reader’s Digest has published hundreds of travel stories that help readers explore the world safely, easily and affordably. We regularly cover topics such as the best places to visit (and the best times to visit them), tips and tricks to zoom through airport security, flight-attendant secrets, hotel-room hacks and more. We’re committed to producing high-quality content by writers with expertise and experience in their field in consultation with relevant, qualified experts. We rely on reputable primary sources, including government and professional organizations and academic institutions as well as our writers’ personal experiences where appropriate. We verify all facts and data, back them with credible sourcing and revisit them over time to ensure they remain accurate and up to date. Read more about our team, our contributors and our editorial policies.
Sources:
- Jason Tetro, microbiologist, author of The Germ Code and The Germ Files, and host of the Super Awesome Science Show podcast; email interview, May 18, 2025
- CDC: “Two Outbreaks of Legionnaires Disease Associated with Outdoor Hot Tubs for Private Use”
- CDC: “What You Can Do to Stay Healthy in Hot Tubs”
- Mayo Clinic: “Legionnaires’ Disease”
- Microbiology Spectrum: “Infections on Cruise Ships”
