Skip to Main Content

Reducing Legionella risks on cruise ships

The Global-Fleet Is Expected To Grow

With 125 new cruise ships set to enter the world’s by 2027, boosting the number of ships to over 550 and providing capacity for about 40 million guests per year, maintaining passenger health is of great importance.

While larger, newer passenger ferries and cruise ships have been built with more advanced sanitation solutions and adopted preventive measures – like encouraging passengers to sanitize hands upon entry to public spaces – the close proximity of thousands of passengers is bound to pose a public health challenge. Little has been done to protect passengers aboard smaller, older ships which, in many cases, have older water systems that are not as well maintained.

This was evident from the research paper Legionella Risk Assessment in Cruise ships and Ferries, published in June 2017 by the US National Institutes of Health’s National Library of Medicine.

Legionella Pneumophila

Researchers evaluated the frequency and severity of Legionella contamination on 10 ferries and six cruise ships alongside or in transiting the Port of Messina, Sicily.  From the water and air samples tested for qualitative and quantitative identification of Legionella, the researchers found that Legionella pneumophila serogroup1, which is most frequently associated with cases of Legionnaires’ Disease, was present in samples of the shower and tap water in 70% of the 10 ferries examined, and in 33% of the six cruise ships examined. They found Legionella pneumophila serogroups 2-14 in samples from 80% of the ferries and in samples from 16% of the cruise ships that were examined. While Legionella contamination was not found in whirlpool bath, air or ice samples, they concluded that the “data confirmed higher levels of Legionella contamination in local ferries and cruise ships, underlining the need to adopt corrective actions more specific for these smaller vessels.

Other than legionellosis, the World Health Organisation (WHO) identified more than 100 disease outbreaks associated with ships in the past 30 years, including meningococcal meningitis, hepatitis A, gastrointestinal infections, influenza, and norovirus.


The most common source of onboard waterborne pathogens, such as Legionnaires’, is from air and water cooling systems, faucets, showers, whirlpools, hot tubs, and inline filters.  Water heater temperatures under 50 degrees Celsius may increase the risk of Legionnaires’ disease due to bacterial growth in the tank, and the risk is particularly significant between 40 and 50°C.


It is imperative that a water management program be put in place to prevent the outbreak of waterborne pathogens. A key aspect of the management plan is to frequently sample and monitor the water systems. If samples suggest the proliferation of the Legionella bacteria then immediate action needs to be taken. This should include a risk analysis to find the root cause of the proliferation. One very effective way to do this is through microbial mapping of the network by sampling and analyzing the water in different locations in order to identify the main proliferation.

Some possible corrective actions include adjustment of water temperatures or the flushing of system pipework.

At LuminUltra we know the shipping industry is required to test their ballast water discharge for organisms, but on-board testing of water systems is imperative as well, to maintain public health, not to mention a ships’ reputation.  Check out our primer on how qPCR testing can be used as a quick screening tool for both investigative and routine monitoring for Legionella.

Carine Magdo

Carine comes to LuminUltra with extensive knowledge in biology, the water treatment technical/systems field, and the global marine industry - making her our resident expert on ballast water monitoring. This knowledge, along with being a member of the new ISO standard for ballast water sampling and analysis, makes her an invaluable resource to shipping companies and Port Authorities as they navigate new regulations around ballast water sampling and testing.

When she’s not on a plane travelling across countries on business or pleasure, she’s riding her horse “Azura” and fulfilling the role of VP of an Equestrian Tourism Association, in the Yvelines in France.

Related Posts

Your browser is out of date!

Update your browser to view this website correctly. Update my browser now