CDC Identifies Cruise Ship Hot Tubs as Likely Source of Legionnaires’ Disease Outbreaks

According to a report from the Centers for Disease Control and Prevention, two outbreaks of Legionnaires’ disease on cruises are likely linked to private hot tubs located on board.

Between November 2022 and June 2024, the CDC was alerted to approximately a dozen cases involving passengers on two different ships. This illness is a serious form of pneumonia caused by the legionella bacteria.

In one incident, eight passengers fell ill, including one probable case, while in the other, four passengers experienced sickness. The report does not disclose the names of the ships or the cruise lines involved.

The CDC’s report, dated October 24, 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.”

In the initial report, a cruise ship identified as Ship A was found to have legionella present in six out of its ten private balcony hot tubs. The report detailed, “Of the six private balcony hot tubs with Legionella detections, four had concentrations of Legionella greater than 100 colony-forming units (CFU)/mL, and two had concentrations exceeding 1,000 CFU/mL.” It was noted that these hot tubs were kept closed until updates were made to their operational and maintenance protocols, resulting in nondetectable Legionella levels.

This particular outbreak was highlighted as the most significant one investigated by the health agency in the cruise industry since 2008.

Similarly, legionella was also detected in cruise ship B’s eight private balcony hot tubs, which were subsequently closed “until nondetectable Legionella post-remediation sampling results were achieved.”

Out of the twelve passengers who fell ill, ten required hospitalization, but fortunately, there were no fatalities. It is noteworthy that merely two guests occupied cabins with balcony hot tubs; however, the report indicated that these “contained within private spaces can still release aerosols into shared areas, leading to potential exposure, even for individuals who do not utilize the hot tubs.”

The cruise lines have adhered to CDC guidelines for managing private hot tubs; however, a recent report indicated that these measures were “insufficient” in preventing bacterial growth.

Cruise ship medical facilities: What happens if you get sick or injured (or bitten by a monkey)

During the investigations, the cruise companies notified both guests and crew about the risk of legionella exposure. The report revealed that “both cruise lines ultimately adjusted their operations and maintenance protocols for the private hot tubs. Heating elements were taken out; tubs were filled only upon guest request, drained after each use, and cleaned and disinfected more often.”

Furthermore, filtration components were eliminated from devices aboard cruise ship A. Both vessels are currently still undergoing sampling.

Richard Miller, founder and president of Environmental Safety Technologies, Inc., mentioned to USA TODAY last year that small amounts of legionella are often found in the water used on cruise ships for drinking, showers, and various amenities. Typically, these concentrations are not enough to lead to illness.

However, the bacteria can thrive in warm water environments. “They just have to manage that and keep it from replicating,” he remarked at that time.

The CDC pointed out in their report that several patients indicated other potential exposure sites during their travels, such as hotels and shore excursions at ports of call, yet emphasized that the cruises were the only shared exposure among the travelers.

Nathan Diller is a consumer travel reporter for USA TODAY based in Nashville. You can reach him at ndiller@usatoday.com.

This piece was initially published on USA TODAY: Cruise ship hot tubs likely exposed travelers to legionella, CDC finds

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