A federal report on two unrelated Legionnaires' disease outbreaks at hotels in the U.S. Virgin Islands found Legionella bacteria in guest room water systems, including cold water lines that stay warm enough in tropical heat for the bacteria to grow.
Legionella is often linked to hot water systems because the bacteria grow best between 77 and 113 degrees Fahrenheit. In a tropical climate, cold water lines can also fall within that range. The report's authors said the findings show the need for Legionella control guidance tailored to warm climates.
For travelers, the lesson is not that Caribbean hotels are unsafe. It is that anyone who develops pneumonia after a trip should tell a clinician where they traveled and stayed.
Inside the Sampling Results at the Two Properties
The CDC report, published July 2 in Morbidity and Mortality Weekly Report, was written by a CDC Epidemic Intelligence Service officer and staff from the U.S. Virgin Islands Department of Health. It describes two separate clusters on St. Croix.
In November 2024, the territorial health department was notified of two confirmed Legionnaires disease cases among travelers who had stayed at two different hotels. Investigators identified two more probable cases among travel companions. The four patients were 53 to 73 years old. Two were hospitalized, and none died.
The results differed between the two properties. At hotel A, Legionella pneumophila was found in three of 21 samples: one showerhead, the cistern, and a water supply pipe. All three positive samples came from cold water sources with temperatures of 80 to 87 degrees. At hotel B, the bacteria were found in 22 of 40 samples, including samples from six sinks and four showers. Those positive samples came from both cold and hot water sources, with temperatures from 82 to 118 degrees.
Two findings stood out. Free chlorine, the disinfectant that helps control bacterial growth, was below the detectable limit in eight samples at hotel A and one at hotel B. At hotel B, bacteria were also found in water above 113 degrees, the top of the optimal growth range, which showed that the bacteria could survive across a wide range of temperatures.
Both hotels used mixed water supplies, including cisterns, municipal water, and private deliveries such as water trucks. In the U.S. Virgin Islands, cisterns are large storage tanks, typically built into building foundations, that collect untreated rainwater from roofs. The report notes that poorly maintained cisterns can harbor germs and are difficult to clean, monitor, and disinfect.
The Surveillance Gap the Investigation Exposed
The report's most important finding may be about how outbreaks are detected.
Although Legionnaires' disease is nationally notifiable, hotel B's outbreak was identified only because a member of the public reported it to the health department.
The authors said many travel-associated cases are likely missed because travelers return home before they get sick. Symptoms usually begin 2 to 14 days after exposure, according to the CDC, so a patient may be diagnosed far from the place where the exposure occurred. The authors said including travel destinations in case reports sent to the CDC is essential to help health departments identify outbreaks and their sources.
The link between the hotels and the illnesses was not confirmed genetically. No lower respiratory samples were available from any patient, so investigators could not compare bacteria from patients with bacteria found in the water.
Both hotels completed cleanup and were cleared to reopen. Hotel A closed the guest room where the first two patients stayed, replaced the showerhead and plumbing, treated the system with high levels of chlorine, and permanently closed the cistern where bacteria were found. It was cleared to fully reopen after follow-up testing showed the water system was under control. Hotel B was required to close entirely. It replaced plumbing and fixtures and was cleared to reopen after testing no longer detected the bacteria. The territory's health department announced that it had ordered Hotel on the Cay to cease operations while the property was cleaned and retested.
Who Should Pay Attention and What to Watch For
Most people exposed to Legionella do not get sick. The report notes that Legionnaires' disease has a low attack rate of 1% to 6%.
Some people face higher risk. According to the CDC, they include adults 50 and older, current or former smokers, people with chronic lung disease, and people with weakened immune systems, cancer, or conditions such as diabetes, kidney failure, or liver failure. All four patients in this report were 53 or older.
The CDC says symptoms of Legionnaires' disease include cough, fever, headache, muscle aches, and shortness of breath. Confusion, diarrhea, or nausea can also occur. Because the illness resembles other types of pneumonia, travel history is especially important. In general, it does not spread from person to person.
A returning traveler with these symptoms should seek medical care and tell the clinician where they traveled and stayed. That information can prompt appropriate testing and treatment and help health officials investigate a property before other guests are exposed. Severe shortness of breath, chest pain, high fever, or new confusion needs urgent care.
This is not only a travel issue. MedicalDaily has reported on a Legionnaires cluster in the South Bronx, where New York City officials ordered cooling towers cleaned.
For hotel operators, the report offers specific guidance. Citing the CDC Legionella control toolkit, it says water management programs should keep hot water storage above 140 degrees and circulating hot water above 120 degrees. The authors also said health officials investigating outbreaks in tropical areas should consider water systems without temperature control and alternative storage systems such as cisterns.
Key Questions Answered
What happened? Two unrelated Legionnaires' disease outbreaks were identified at two St. Croix hotels in November 2024. Four travelers aged 53 to 73 became ill, two were hospitalized, and none died.
Where were the bacteria found? In guest room showers at both hotels, in the cistern and cold water system at hotel A, and in both cold and hot water systems at hotel B.
Why do cold water lines matter here? In tropical climates, cold water can reach temperatures between 77 and 113 degrees Fahrenheit, the range where Legionella grows best.
How likely is illness after exposure? Low. The report cites an attack rate of 1% to 6%, and most healthy people exposed to Legionella do not get sick.
Who faces the highest risk? Adults 50 and older, current or former smokers, people with chronic lung disease, and people with weakened immune systems or certain chronic illnesses.
What symptoms should travelers watch for? Cough, fever, headache, muscle aches, and shortness of breath, usually 2 to 14 days after exposure.
What should I tell my doctor? Where you traveled and where you stayed. That can prompt the right testing and help health officials investigate.
