According to a newly published report from the Centers for Disease Control and Prevention (CDC), two separate outbreaks of Legionnaires’ disease on cruise ships are likely linked to private hot tubs located onboard.
The health authority reported a total of approximately a dozen cases of the illness, which is categorized as a severe form of pneumonia caused by legionella bacteria, in the period between November 2022 and June 2024 among passengers aboard the two vessels.
On one vessel, noted in the report as cruise ship A, eight individuals fell ill—one of whom was classified as a probable case—while four passengers on the second ship experienced similar health issues. The report has deliberately refrained from identifying the specific cruise lines or ships involved.
In the report dated October 24, the CDC stated, “Epidemiologic data collected from patient interviews and environmental assessment and sampling results identified private hot tubs on selected cabin balconies as the most likely exposure source.”
For the first vessel, marked as cruise ship A, the bacteria were discovered in six out of ten private balcony hot tubs. The report detailed, “Of the six private balcony hot tubs with Legionella detections, four had concentrations of Legionella >100 colony-forming units (CFU)/mL, and two had concentrations >1,000 CFU/mL.” Consequently, these hot tubs were closed until the operational and maintenance guidelines were revised and the samples returned with nondetectable results for Legionella.
This outbreak constituted the largest investigated by the CDC on cruise ships since 2008, emphasizing a concerning trend in onboard health safety. Legionella was also identified in the eight private balcony hot tubs on cruise ship B, and similar containment protocols were implemented until the bacteria were cleared from the system through postremediation sampling.
Among the twelve passengers who experienced illness, ten required hospitalization, though thankfully, there were no reported fatalities. Interestingly, only two of the affected guests occupied cabins that included balcony hot tubs, demonstrating that even private facilities can release aerosols into communal areas, leading to unintentional exposure for non-users of the hot tubs.
The cruise lines had been adhering to CDC mandates for the operation of private hot tubs; however, the report indicated that these guidelines proved to be “insufficient” in preventing the growth of the dangerous bacteria.
As investigations were underway, the cruise companies informed guests and crew members of the potential risk of legionella exposure. “Both cruise lines ultimately modified the operation and maintenance of the private hot tubs so that heating elements were removed; tubs were only filled upon guest request, drained between uses, and cleaned and disinfected more frequently,” the report elaborated.
Additional filtration components were dismantled from the devices on cruise ship A as part of the updates. Ongoing sampling is still taking place on both ships to ensure safety and compliance with health standards.
Richard Miller, the founder and president of Environmental Safety Technologies, Inc., shared insights last year with USA TODAY indicating that while small amounts of legionella are often found in the water used for drinking, showers, and various amenities on cruise ships, these levels typically do not pose a significant health risk.
Nevertheless, the bacteria can thrive in warm water environments. “They just have to manage that and keep it from replicating,” Miller advised regarding the challenges of water safety onboard.
The CDC report also mentioned that several patients had identified other potential exposure sites during their travels, including hotels and excursions at ports of call. However, it was noted that the cruises were the only common factor among the affected travelers.
Nathan Diller is a consumer travel reporter for USA TODAY based in Nashville. You can reach him at ndiller@usatoday.com.
