Luxury or Liability? CDC Sounds Alarm on Legionnaires’ Disease in Cruise Ship Hot Tubs

For those who think cruising is all about relaxation, recent CDC investigations have highlighted a hidden hazard lurking on board: Legionnaires’ disease. Between November 2022 and June 2024, the CDC linked 12 cases of Legionnaires’ disease to two cruise ships after guests fell ill with severe pneumonia caused by Legionella bacteria. CDC findings pointed to private balcony hot tubs — increasingly popular on modern cruise ships — as the likely exposure source, leading to a series of safety upgrades and maintenance changes across the industry.

Private Hot Tubs: A Breeding Ground for Legionella

These private hot tubs, positioned on individual cabin balconies, were found to create favorable conditions for Legionella growth when inadequately maintained. Unlike public hot tubs in common areas, private tubs aren’t required to have automated, continuous disinfectant dosing or pH monitoring. Instead, current CDC guidelines only mandate that they be shock-chlorinated, drained, and refilled weekly or between occupancies. Despite adherence to these standards, Legionella bacteria thrived, leading the CDC to investigate further.

The issue first surfaced on what the CDC has identified only as Ship A, where the CDC identified five cases of Legionnaires’ disease among passengers on the same November 2022 voyage. By August 2023, after more cases were linked to private balcony hot tubs, CDC requested all 10 balcony tubs on Ship A be shut down and tested. Six of the tubs tested positive for Legionella, with levels in some tubs reaching over 1,000 colony-forming units per milliliter. Meanwhile, another ship, Ship B, saw similar issues, with eight private tubs testing positive for Legionella serogroups Lp1 and Lp2–14.

Steps Taken to Combat Legionella

In response to the Legionella outbreak, cruise lines implemented strict new maintenance protocols for private hot tubs. These measures included disabling the heating functions to prevent temperatures conducive to bacterial growth, keeping tubs empty until requested by guests, and implementing more frequent draining, cleaning, and disinfection between uses. Additionally, more rigorous chlorination practices were introduced, with Ship A even removing filtration systems from these tubs. These efforts were complemented by ship-wide hyperchlorination and increased water sampling to ensure Legionella levels remained undetectable. The comprehensive approach aimed to address the root causes of bacterial growth and prevent future outbreaks, demonstrating the cruise lines’ commitment to passenger safety.

An Ongoing Public Health Concern

Legionnaires’ disease has long been recognized as a risk in the travel industry, particularly on cruise ships, where water systems and recreational amenities require stringent maintenance. While public hot tubs on cruise ships are subject to continuous monitoring for disinfectant levels and pH, this isn’t required for private balcony tubs. This oversight may have allowed Legionella to thrive undetected, posing a health risk to unsuspecting passengers.

To prevent future outbreaks, the CDC is urging cruise lines to include private hot tubs in water management programs and to adapt public hot tub maintenance protocols for private units. These updated protocols could help prevent Legionella growth, particularly in hot tubs located on open-air balconies where water temperature and cleanliness are harder to regulate.

The Takeaway

As cruise lines work to reduce the risk of Legionnaires’ disease on board, passengers may want to be wary of private hot tubs, which, while luxurious, come with hidden risks. This new public health insight serves as a reminder that even the most indulgent amenities can harbor unseen dangers if not managed properly.

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