Twelve cases of Legionnaires' disease were reported among passengers on two cruise ships between November 2022 and June 2024.

The regulations applied to private hot tubs are lenient, and when improperly maintained and run, they provide ideal conditions for Legionella development and transmission.

Aerosols from private hot tubs can transfer diseases to public spaces.

The researchers advise cruise ship water management personnel to inventory and assess private balcony hot tubs and modify public hot tub maintenance and operating protocols for private outdoor hot tubs.