The US Centres for Disease Control and Prevention (CDC) recently warned of outbreaks of Legionnaires’ disease, a serious form of pneumonia, connected to two cruise ships’ private hot tubs. Twelve people were impacted by the outbreaks, which happened between November 2022 and July 2024, according to the CDC’s report on October 24.

The CDC acknowledged in a report that both cruise ships provided European, Caribbean, and Mediterranean routes, but it did not provide the identities of the ships. Since private-use hot tubs were found to be the source of the bacterial illness, the CDC cautions travellers about the health hazards involved.

What is Legionnaires disease?

According to the CDC, Legionnaires disease is a serious pneumonia caused by Legionella bacteria. Hot tubs can be a source of Legionella growth and transmission when they are inadequately maintained and operated.

What is added by this report?

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. These devices are subject to less stringent operating requirements than are public hot tubs, and operating protocols were insufficient to prevent Legionella growth.

What are the implications for public health practice?

It is important for cruise ship operators to inventory hot tub-style devices across their fleets, evaluate the design features that increase the risk for Legionella growth and transmission, and test for Legionella.

Given the range of hot tub-type devices offered as amenities across the cruise industry, to reduce risk for Legionella growth and transmission, it is important for cruise ship water management program staff members to inventory and assess private balcony hot tubs and adapt public hot tub maintenance and operations protocols for use on private outdoor hot tubs.