People staying in short-term rental properties should be aware that hot tubs might pose a risk of a potentially fatal type of pneumonia, according to a new paper in the Morbidity and Mortality Weekly Report (MMWR) from investigators with the New York State Department of Health (NYSDOH) and other state agencies. 

The paper details a 2024 outbreak of Legionnaires’ disease in western New York among two guests who used a hot tub at a private short-term rental property. 

Whole-genome sequencing of isolates from the hot tub were found to be closely related to the laboratory results of one of the patient’s mucus and phlegm, which suggests the hot tub as the likely source of exposure. 

Hot tubs a common exposure source

Nearly one in seven Legionnaires’ disease patients report staying overnight at hotels, private homes, or vacation rental properties, according to the Centers for Disease Control and Prevention (CDC). About half of those with a travel-associated case say they soaked in a hot tub. 

Private short-term rental properties are not subject to the same public health regulations as commercial properties. The report says vacationers should be aware of this risk, especially older adults, people with weakened immune systems, and people who smoke.

The water in the hot tub implicated in the 2024 outbreak was at 100°F to 104°F, which is within “the most favorable range for Legionella growth and also accelerates the decay of disinfectants,” said the report.

People most often get Legionnaires’ by breathing mist carrying the Legionella bacteria. Small, heated pools are vulnerable to Legionella bacteria, as they are filled with warm water that’s slowly moving or stagnant. While most cases can be treated successfully with antibiotics, roughly one in 10 people who get sick from Legionnaires’ disease die from complications linked to the illness.

Owner ignored orders to close

For a short time, the hot tub implicated in the MMWR report was deemed a public nuisance and ordered to close.

The owner of the rental initially disregarded guidance from the NYSDOH and CDC to close the hot tub until proper remediation was performed and samples free of Legionella bacteria were collected by NYSDOH scientists. The listing continued to advertise the hot tub, and guests were still leaving reviews mentioning it, until public health officials intervened. 

“The rental property owner had personally cleaned the hot tub (i.e., did not hire professionals), tested a sample using an unapproved method, and reopened the hot tub for guest use without consulting NYSDOH,” explained the report.

The rental property subsequently hired a professional cleaner to service the hot tub weekly. After two successive rounds of sampling were clear of viable Legionella organisms, the hot tub was again available to guests. 

To keep hot tubs healthy, the CDC recommends people install an automatic disinfectant system rather than handfeeding disinfectant.

Around the time of the outbreak, there was a separate cluster of three other Legionella cases in the area, though no common exposures were identified.