Recent outbreaks of Legionnaires’ disease have been linked to U.S. cruise ship hot tubs, according to reports.

Private outdoor hot tubs on the balconies of two cruise ships were pinpointed as the source of multiple infections between November 2022 and June 2024, as stated in a report last month from the Centers for Disease Control and Prevention (CDC).

“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 said in the report.  

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Hot tubs can foster Legionella bacteria due to their warm temperatures, which are ideal for bacterial growth, according to Waleed Javaid, MD, epidemiologist and director of infection prevention and control at Mount Sinai Downtown in New York. 

“The bubbling and aerosolization make it easy for bacteria to be inhaled, which is the primary way people get infected,” Javaid, who was not affiliated with the CDC report, told Fox News Digital.

What to know about Legionnaires’ disease

Legionnaires’ disease is a type of pneumonia caused by Legionella bacteria. 

The bacteria can grow in any area where water sits for a long time, according to Dr. Andrew Handel, a pediatric infectious diseases expert at Stony Brook Children’s Hospital on Long Island, New York.

When people swallow or breathe in droplets of water that contain Legionella, they can potentially become ill.

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Although human transmission is possible in rare cases, the disease is not typically spread from person to person, per the CDC.

Infections can lead to severe pneumonia in older people and those with compromised immune systems, Handel warned.

“Legionella infections cause symptoms that are similar to other forms of pneumonia — fever, coughing, difficulty breathing, shortness of breath and chest pain,” said Handel, who also was not involved in the CDC report.

Some patients may also experience nausea, diarrhea and confusion, the CDC noted. 

A medical professional can diagnose the infection with laboratory tests and chest X-rays.

The condition is typically treated with antibiotics. In cases of severe infection, hospitalization may be required for breathing support and IV hydration.

Around 10% of people who contract Legionnaires’ disease will die from those complications — and the mortality risk rises to 25% for those who get Legionnaires’ while staying in a health care facility, according to the CDC.

Around 10% of people who contract Legionnaires’ disease will die from complications, according to the CDC.

If someone suspects they were exposed to Legionella bacteria, it is important to see a health care professional right away, as early intervention may increase the chances of a full recovery, infectious disease experts told Fox News Digital.

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“If you’ve recently used a hot tub and are worried about Legionnaires’ disease, watch for symptoms like cough, shortness of breath, fever, muscle aches and headaches,” which can appear anywhere from two to 14 days after exposure, Javaid advised.

“Act quickly if you notice these signs, especially if you fall into a vulnerable category,” he added.

The CDC’s findings

Twelve cases of Legionnaires’ disease were reported among cruise ship passengers on two different vessels, according to the CDC report. 

Out of the dozen sickened individuals, 10 were hospitalized. No deaths were reported. 

The cruise ship companies were not identified in the report, and were only named as cruise ships A and B.

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The CDC determined that the private hot tubs were operating in ways that fostered Legionella growth. 

These conditions included water running at temperature ranges of 77 to 113 degrees Fahrenheit for several days, “without draining and operating with no residual disinfectant,” according to the report.

The report also noted that individuals could have been exposed without using the hot tubs, which were located near outdoor areas where aerosols could be disseminated.

Private hot tubs on cruise ships are subject to “less stringent operating requirements than public hot tubs,” the agency noted.

Ships A and B did adhere to the current CDC requirements for operating and maintaining private hot tubs, but these steps were not sufficient to prevent Legionella growth.

The cruise ships cooperated with the investigation and made efforts to mitigate Legionella growth, per the CDC report.

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To reduce the risk of bacterial growth and transmission, the CDC recommends that owners and operators of hot tubs follow safe operation and maintenance procedures to prevent exposure to Legionella. 

“Additionally, an automatic disinfectant dosing system, rather than handfeeding disinfectant, is an important design feature to help prevent growth,” the CDC said in a statement sent to Fox News Digital.

Enjoying hot tubs safely

The experts shared steps people can take to minimize exposure to bacteria when using hot tubs.

“I advise people who are worried to stay informed, but not alarmed,” Javaid said. 

“I also advise keeping an eye on the hygiene standards of hot tubs in public spaces, especially if you are someone at higher risk.”

It’s reasonable for cruise-goers to ask questions about how hot tubs are maintained and disinfected, Javaid said, and it’s best to avoid hot tubs that “smell strange or seem poorly kept.”

“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.” 

“Certain populations should exercise extra caution, including individuals of advanced age, smokers, people with chronic lung conditions and immunocompromised people,” the expert added, noting that these groups are particularly vulnerable to Legionnaires’ disease.

Handel echoed that hot tub owners should follow health guidance on maintaining sterile water and machinery.

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“While properly maintained hot tubs can be safe, people who are older or are immunocompromised may want to speak with their medical providers before using one,” Handel cautioned. 

“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.” 

The CDC provided the following general recommendations to Fox News Digital.

“Some general practices to prevent Legionella as well as other waterborne germs at home include flushing faucets and showerheads after not using them or water pressure drops, cleaning and maintaining devices that use water (e.g. humidifiers, nasal rinses, showerhead and faucet aerators, water filters), and checking and flushing water heaters.”

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On a brighter note, Handel noted that there have been some improvements in water treatment and monitoring, which has resulted in Legionella infections becoming less common.

Currently, there are no vaccines for Legionnaires’ disease. 

Fox News Digital reached out to four popular cruise lines to discuss their hot tub maintenance protocol, but had not heard back as of publication.

Fox News’ Melissa Rudy contributed reporting.