Cruise Legionnaires’ outbreaks linked to private onboard hot tubs

Two Legionnaires’ disease outbreaks on cruises likely stemmed from private hot tubs onboard, according to a new report from the Centers for Disease Control and Prevention.
The health agency was notified between November 2022 and June 2024 about a dozen cases among passengers on two ships. The illness is a severe kind of pneumonia caused by legionella bacteria.
Eight travelers on one ship became ill – including one probable case – while four on the other were sickened. The report does not name the vessels or the cruise lines.
“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,” the CDC said in the report dated Oct. 24.
On the first vessel, referred to in the report as cruise ship A, legionella was found in six of its 10 private balcony hot tubs. “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,” the report said. “The hot tubs remained closed until their operation and maintenance protocols were modified and nondetectable Legionella sampling results were obtained.”
The outbreak on that ship was the biggest investigated on cruises by the health agency since 2008.
The bacteria was detected in cruise ship B’s eight private balcony hot tubs as well and were closed “until each had nondetectable Legionella postremediation sampling results.”
Among the 12 ill passengers, 10 were hospitalized. There were no fatalities. Only two of the guests stayed in cabins with balcony hot tubs, but even those “located in private areas can disseminate aerosols to common areas and result in exposures, even in persons who do not use the hot tubs themselves,” according to the report.
The cruise lines had followed CDC requirements for operating private hot tubs, but the report said those were “insufficient” to keep the bacteria from growing.
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The cruise companies altered guests and crew members to the possibility of legionella exposure during the investigations. “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 said.
Filtration elements were also removed from devices on cruise ship A. Both vessels are still undergoing sampling.
Small amounts of legionella are frequently present in the water cruise ships use for drinking, showers and other amenities, Richard Miller, founder and president of Environmental Safety Technologies, Inc., told USA TODAY last year. But those quantities are not usually high enough to cause illness.
The bacteria can grow in an environment like warm water, however. “They just have to manage that and keep it from replicating,” he said at the time.
The CDC noted in the report that a number of “patients reported other possible exposure locations during their travel, such as hotels and shoreside excursions at ports of call,” but said the cruises were the only exposure the travelers had in common.
Nathan Diller is a consumer travel reporter for USA TODAY based in Nashville. You can reach him at [email protected].