By Ethan Covey
Private balcony hot tubs were likely the source of outbreaks of Legionnaires disease that occurred on two cruise ships between November 2022 and July 2024, according to the CDC.
In total, 12 cases of Legionnaires disease were identified among cruise ship travelers (MMWR Morb Mortal Wkly Rep 2024;73:950–954).
“Travel on cruise ships is a recognized risk factor for Legionnaires’ disease due to exposure to aerosolizing devices, for example, hot tubs, onboard and the complex nature of the ships’ potable water systems,” said Sooji Lee, MSPH, an epidemiologist at the CDC’s National Center for Immunization and Respiratory Diseases.
“Hot tubs located on select private cabin balconies, included on some cruise lines, can be a source of Legionella growth and transmission,” Ms. Lee continued. “Previous investigations show that aerosols from private-use hot tubs can spread to common areas and potentially expose people who don’t have access to these hot tubs. This is especially important, as private hot tubs have become more common as new ships enter service and older ones are renovated.”
On cruise ship A, a total of eight cases were identified—seven laboratory-confirmed and one probable—in passengers who had taken voyages from November 2022 through April 2024.
While staff on the vessel had conducted Legionella environmental sampling, the 10 private balcony hot tubs had not previously been tested. Once they were tested, in August 2023, Legionella pneumophila serogroup 2-14 (Lp2-14) and non-pneumophila Legionella species were detected in six of the 10 hot tubs.
“Private hot tubs on cruise ships are not subject to the same maintenance requirements as are public hot tubs in common areas,” Ms. Lee and her colleagues wrote in the report.
On cruise ship B, four Legionnaires’ disease cases were confirmed among travelers who had participated in voyages from January through June 2024. L. pneumophila serogroup 1 (Lp1) and Lp2-14 species were detected in all eight private balcony hot tubs on the ship. Additionally, Lp2-14 was detected in a single location in the potable water system.
Although most healthy people exposed to Legionella do not develop Legionnaires’ disease, certain people are at increased risk of getting sick, including those 50 years of age and older, current or former smokers, and people with weakened immune systems or chronic diseases.
“Those at increased risk may consider talking with a healthcare provider about their health and risk factors prior to arranging travel,” Ms. Lee said.
Each of the cruise lines ended up modifying the operation and maintenance of private hot tubs so that heating elements were removed, tubs were only filled upon guest request, were drained between uses, and cleaned and disinfected more frequently.
“Since there is a wide range of hot tub–style devices, the cruise industry could benefit from performing a fleetwide assessment and inventory of devices and their features that increase the risk for Legionella growth and transmission and developing prevention messages for guests and crew,” Ms. Lee said. “Additionally, cruise investigations could benefit from the continued efforts of state and local health departments in conducting in-depth case patient interviews.”
The sources reported no relevant financial disclosures.
