Legionella Even Tries to Get You on Vacation: Why Cruise Ships Need Serious Water Management

When most people picture a cruise vacation, they think about ocean views, warm weather, pools, hot tubs, restaurants, and a week away from the everyday grind.

They probably are not thinking about what is happening inside the miles of piping behind the walls of the ship.

But Legionella is.

Legionella bacteria do not care whether the water system belongs to a hospital, hotel, senior living community, manufacturing facility, or luxury cruise ship. Give the bacteria the right conditions, including warm water, stagnation, biofilm, and insufficient disinfectant, and they can multiply.

The CDC identifies temperatures between approximately 77°F and 113°F as favorable for Legionella growth. Slow or stagnant water, biofilm, and inadequate disinfectant can further increase the risk.

A cruise ship happens to contain a lot of those potential environments.

Cabin showers. Sinks. Hot tubs. Pools. Spas. Decorative water features. Storage tanks. Hot and cold potable water distribution. Recirculation systems. Long piping runs. And hundreds or thousands of individual points of use.

It is essentially a floating building with an extremely complex water system.

Yes, Legionella Has Been Linked to Cruise Ships

This is not theoretical.

In a CDC investigation published in 2024, 12 cases of Legionnaires' disease were associated with travelers aboard two cruise ships between November 2022 and June 2024. Eight cases were connected with one ship and four with another. Ten of the 12 patients were hospitalized.

Investigators ultimately identified private balcony hot tubs as the most likely exposure source.

On one ship, CDC investigators tested 10 private balcony hot tubs and detected Legionella in six of them. Four contained concentrations greater than 100 CFU/mL, and two exceeded 1,000 CFU/mL.

The conditions were almost a textbook example of what Legionella needs.

Some of the hot tubs maintained water within the Legionella growth temperature range for days at a time, retained water between uses, generated aerosols through jets, and operated without a disinfectant residual.

That last piece is especially important.

Legionella exposure typically occurs when contaminated water becomes aerosolized into tiny droplets that can be inhaled. Showers and hot tubs are obvious examples, but the CDC notes that aspiration of contaminated water can also cause infection.

You do not necessarily have to drink contaminated water to become sick.

You can breathe it.

Travel Makes Legionella Particularly Difficult to Track

The CDC Yellow Book describes Legionnaires' disease as less common on cruise ships than many other travel-related illnesses, but still a significant concern because it can cause severe pneumonia and death.

CDC data from 2015 and 2016 identified 35 confirmed Legionnaires' disease cases associated with cruise ship exposure. During that same period, approximately 10% of Legionnaires' disease cases reported to CDC occurred in people who had traveled during the 10 days before symptoms began.

Travel-associated cases create another problem.

By the time someone becomes sick, the vacation may be over.

Passengers leave the ship and scatter across different cities, states, and even countries. They may visit completely different healthcare systems and physicians. Connecting several pneumonia cases back to the same hotel, cruise ship, spa, or other water source can therefore be extremely difficult.

That is one reason prevention matters so much.

For Immunocompromised Travelers, the Risk Is More Serious

Most healthy people exposed to Legionella do not become sick.

But some populations are considerably more vulnerable.

According to the CDC, increased-risk groups include:

• People 50 years of age or older

• Current or former smokers

• People with chronic lung disease

• People with cancer

• People with diabetes

• People with kidney or liver failure

• People with weakened immune systems

• People taking medications that suppress the immune system, including certain chemotherapy and transplant medications

That is especially relevant to the cruise industry.

Cruises attract travelers across a broad age range, including older adults and people who may be managing chronic medical conditions. A water system that might never make one passenger sick could cause severe pneumonia in another.

Water management has to be designed around protecting the vulnerable person, not simply the average healthy occupant.

The Story of Legionnaires' Disease Actually Began With Travel

There is an interesting historical connection here.

The disease received its name following the famous 1976 American Legion convention in Philadelphia.

Most of the people affected had attended the convention at the Bellevue-Stratford Hotel. CDC ultimately documented more than 200 illnesses and dozens of deaths associated with the outbreak, and the investigation eventually led scientists to identify the previously unknown bacterium responsible for the disease.

Nearly 50 years later, the lesson remains remarkably similar.

Large, complicated building water systems can create conditions where Legionella survives and multiplies.

The problem was never limited to hospitals.

Hotels can have it.

Cruise ships can have it.

Resorts can have it.

Apartment buildings can have it.

Senior living communities can have it.

Commercial buildings can have it.

Anywhere you have a complex water system, susceptible occupants, favorable water temperatures, stagnation, biofilm, and inadequate disinfectant, you have conditions that deserve attention.

What Should Cruise Ships Be Doing?

The CDC specifically recommends that cruise operators develop and implement a comprehensive Water Management Program that includes all ship water systems and devices that use water.

That means looking beyond the obvious.

A strong program should identify and manage potable water systems, storage tanks, hot water systems, recreational water, public and private hot tubs, decorative water features, technical water systems, and areas where water can become stagnant.

Operators should also identify locations affected by changes in occupancy or water demand, monitor critical water quality parameters, flush stagnant areas, maintain appropriate temperatures and disinfectant residuals, and use Legionella testing as part of validation when appropriate.

CDC's investigation of the recent cruise ship outbreaks also makes an important point: simply having operating procedures is not enough if those procedures do not actually control the conditions allowing Legionella to grow.

The water system has to be measured.

The results have to be reviewed.

And when conditions are outside the desired range, something has to change.

That Is Where Legionella Specialties Comes In

This is the same philosophy we bring to water systems every day.

At Legionella Specialties, we believe a Water Management Plan should be more than a document sitting in a binder.

You need to know what is actually happening inside the system.

That begins with establishing a baseline. We evaluate water quality indicators throughout the system, identify areas of concern, look for conditions that can support microbial growth, and help develop corrective strategies based on what the water is telling us.

When necessary, that may include flushing and remediation strategies, ongoing monitoring, system adjustments, or secondary disinfection to help maintain control throughout the water distribution system.

Then you continue measuring.

Because water systems change.

Occupancy changes. Temperatures change. Municipal water conditions change. Plumbing changes. Fixtures change. Biofilm develops. Buildings add new wings and equipment. Ships change itineraries, passenger loads, and operating schedules.

A water system that was under control six months ago is not automatically under control today.

You Should Be Managing the Water Before It Becomes an Outbreak

Legionnaires' disease may have become famous because of a hotel convention, but nearly five decades of research have made one point abundantly clear:

Legionella is not a hospital-only problem.

Whether you operate a hospital, hotel, cruise ship, resort, senior living facility, university, commercial property, or any other complex building, understanding your water system matters.

Know your system.

Know where your risks are.

Test it.

Monitor it.

Treat it when necessary.

And have a real plan for keeping it under control.

Because apparently even Legionella likes to go on vacation.

Legionella Specialties Testing. Water Management. Treatment. Ongoing Control.