Passengers relaxing in private balcony hot tubs on luxury cruises never expected their retreat to come with a hidden risk – a severe, sometimes deadly, respiratory infection traced directly to these bubbling waters.
But, a new Centers for Disease Control and Prevention (CDC) investigation has linked these private paradises as the source of a recent outbreak of the infection, known as Legionnaires’ disease, on two major unidentified cruise ships.
A severe form of pneumonia caused by the Legionella pneumophila bacteria, the CDC found 12 cases among passengers who traveled on two cruise ships between November 2022 and July 2024.
“Epidemiologic, environmental, and laboratory evidence suggests that private balcony hot tubs were the likely source of exposure in two outbreaks of Legionnaires disease among cruise ship passengers,” said the CDC.
The CDC first detected issues on “Cruise Ship A,” with five passengers reporting symptoms after a November 2022 voyage. In the following months, cases continued to surface, ultimately impacting eight passengers by April 2024.
In response and at the CDC’s request, the cruise ship conducted comprehensive water samplings from various ship locations, including hot tubs, potable water systems, and public areas.
Legionella bacteria was detected in six of 10 private balcony hot tubs, with some samples showing dangerously high bacteria levels.
Read Also: How Do Cruise Ships Get Rid of Human Waste?
Further investigation revealed similar contamination on “Cruise Ship B,” where Legionnaires’ cases were reported in January, February, and May 2024. Lab tests confirmed the presence of the bacterium in every private hot tub tested, with some samples also dangerously high.
The CDC finds cases of Legionnaires’ disease to be highest among men and older adults. The passengers, of which 100 percent were from the US on Cruise Ship A, were predominantly male and over the age of 63.
All had been exposed to public and private hot tubs during their voyage, with 63 percent of guests from the first vessel also found to have used the spa.
Seventy-five percent of the cases from Cruise Ship A required hospitalization, while 100 percent from Cruise Ship B were hospitalized. All the passengers survived.
Although the CDC did not reveal the cruise ships, Norwegian Cruise Line and Celebrity Cruises confirmed cases of Legionnaires’ disease aboard Norwegian Prima and Celebrity Ascent, respectively, which coincide with the CDC’s investigation timeline.
Stricter Cleaning Guidelines Recommended
While the CDC’s investigation found the contamination in hot tubs on the balconies of private suites, the most expensive and exclusive stateroom options available on cruise ships, hot tubs on vessels are also found on open decks near swimming pools and in cruise ship spas.
However, public hot tubs often undergo a rigorous cleaning program, including continuous disinfectant dosing and pH monitoring through automated systems that regulate and maintain safe levels of both. Kids who are not potty trained are also not allowed to go into a hot tub.
As the outbreaks occurred in private hot tubs, the CDC has issued broader guidance for cruise ships, suggesting more rigorous maintenance standards beyond the current weekly chlorination recommendation.
In fact, the CDC is encouraging cruise ships to implement continuous disinfectant dosing and pH monitoring for private hot tubs, similar to what is already required for public tubs.
In cases where continuous dosing isn’t feasible, the CDC advises thoroughly shock-chlorinating hot tubs after each guest to minimize contamination risks.
It also recommends draining and disinfecting hot tubs thoroughly after each use rather than retaining water between guests, as well as removing and cleaning heating elements and filtration systems that can trap bacteria.
