CDC Warns Private Hot Tubs on Cruise Ships Cause Legionnaires’ Disease

The Centers for Disease Control and Prevention (CDC) has issued an urgent warning about private hot tubs on cruise ships after linking them to multiple outbreaks of Legionnaires’ disease. A recent CDC investigation found that these luxury amenities were the “likely source of exposure” in outbreaks affecting 12 cruise passengers, with 10 requiring hospitalization.

The report, published in the CDC’s Morbidity and Mortality Weekly Report, details how private balcony hot tubs lack the stringent maintenance protocols required for public hot tubs, creating ideal conditions for Legionella bacteria to flourish. This finding could impact thousands of high-end cruise suites that feature private hot tubs as premium amenities.

Largest Outbreak Since 2008 Traced to Private Amenities

Between November 2022 and June 2024, the CDC identified 12 cases of Legionnaires’ disease across two cruise ships, with eight cases on one vessel representing the largest cruise-associated outbreak in over 15 years. According to the CDC report, passengers who contracted the serious lung infection experienced symptoms after returning home from their voyages.

Initial investigations focused on common water sources such as the ships’ public hot tubs, potable water systems, and decorative fountains. However, after testing multiple private balcony hot tubs, the CDC found alarming levels of Legionella bacteria in these facilities, with some tubs showing concentrations exceeding 1,000 colony-forming units per milliliter.

“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,” the CDC stated in their report. They further noted that these devices were “subject to less stringent operating requirements than are public hot tubs, and operating protocols were insufficient to prevent Legionella growth.”

Ideal Conditions for Dangerous Bacteria

Hot tubs create perfect breeding grounds for Legionella bacteria due to their warm water temperatures, which typically range between 77°F and 113°F. While public hot tubs on cruise ships are subject to strict maintenance protocols, including continuous disinfectant monitoring and automated chemical dosing, private hot tubs often lack these safeguards.

Dr. Waleed Javaid, epidemiologist and director of infection prevention and control at Mount Sinai Downtown in New York, explained to Fox News that “the hot, stagnant water has the potential to transmit a number of harmful bacteria and viruses that can cause severe illness in high-risk individuals.”

Investigations revealed that private hot tubs on both ships were “found to be operating for months in a manner conducive to Legionella growth,” including maintaining water temperatures in the Legionella growth range for days without draining and operating with no residual disinfectant.

Airborne Transmission Poses Broader Risk

The investigation uncovered an additional concern: private balcony hot tubs may pose risks not just to those using them, but to other passengers as well. According to Science Alert, because these hot tubs are often located on balconies, the vapor and splashes could easily spread to neighboring cabins, including those above and below.

Legionella bacteria spread through water droplets or mist that can be inhaled, meaning passengers walking on decks near or below private hot tubs could be exposed without ever entering the water themselves. This airborne transmission pathway makes the risk particularly concerning in the confined environment of a cruise ship.

“Combining this with the often more at-risk population in cruise ships—this can lead to more cases,” explained Conor Meehan, an associate professor of microbial bioinformatics at Nottingham Trent University. Cruise passengers tend to be older than the general population and therefore potentially more vulnerable to Legionnaires’ disease.

Cruise Lines Implement Safety Measures

In response to the CDC findings, both affected cruise lines took immediate corrective actions. These included disabling heating elements to prevent temperatures conducive to bacterial growth, draining tubs between uses, and implementing more frequent hyperchlorination and cleaning protocols.

The CDC has recommended that all cruise operators inventory hot tub-style devices across their fleets, evaluate design features that increase Legionella risk, and adapt more stringent public hot tub maintenance protocols for private facilities. This may mean significant changes to how luxury suite amenities are marketed and maintained.

“To reduce risk for Legionella growth and transmission, it is important for cruise ship water management program staff members to inventory and assess private balcony hot tubs and adapt public hot tub maintenance and operations protocols for use on private outdoor hot tubs,” the CDC advised in their report.

Health experts recommend that high-risk individuals, including older adults, smokers, and those with weakened immune systems, consult with healthcare providers before using hot tubs on cruise ships. Passengers should inquire about hot tub maintenance protocols before booking suites with these amenities.