was another story: six of 10 private balcony hot tubs tested positive for the bacteria.

In the second outbreak, which took place between January and June, 2024, on cruise ship B, the CDC requested immediate closure of all hot tubs on the ship, including those in both common areas and private balconies.

Legionella was not found in the common areas, but all eight private balcony hot tubs tested positive.

“According to current CDC requirements, private hot tubs are not required to have automated continuous disinfectant dosing and monitoring or pH monitoring, as is standard for public hot tubs,” the CDC stated in their report. “To meet CDC requirements, private hot tubs must only be shock-chlorinated, drained, and refilled weekly or between occupancies, whichever is sooner.

Although the cruise lines adhered to current CDC requirements for operating and maintaining private hot tubs on ships A and B, these measures were insufficient to prevent Legionella growth.”

The authors of the report recommended adapting public hot tub maintenance and operations protocols for use on private balcony hot tubs.