Legionella Outbreak Sparks Call for Immediate Action from Cruise Operators

(Text and images copyright Lion PR, reproduced with kind permission)



Expert warns outdated lab tests may have given false negatives, putting passengers at serious risk

Following the distressing news of yet another Legionella outbreak on a cruise ship, a leading Legionella testing expert has stated that it has never been more critical for cruise lines and holiday operators to prioritise prevention.

According to multiple media reports, two passengers were diagnosed with Legionnaires' disease after sailing aboard the Norwegian Encore in December 2025. In a letter issued to guests on 12 February, the cruise operator confirmed it is working alongside the Centers for Disease Control and Prevention (CDC) to investigate the confirmed cases, adding that, despite conducting Legionella testing onboard, all results so far have come back negative.

The inference of this insight, according to the UK's leader in Legionella testing technology, is that current and largely outdated testing procedures may be failing to identify Viable but non-culturable (VBNC) strains of Legionella that are not active but still have the potential to pose a risk to humans.

Notably, the incident follows several Legionnaires' disease outbreaks linked to cruise ships in recent years. In 2025, Royal Caribbean International confirmed that two guests who had sailed on the Symphony of the Seas were later diagnosed with Legionnaires' disease.2 Between 2022 and 2024 the CDC investigated 12 cases of Legionnaires' disease associated with two cruise ships, ten of which required hospitalisation. One vessel alone accounted for eight infections - constituting the largest outbreak on a single cruise ship since 2008.

With 2026 expected to be yet another record year for cruise bookings, leading Legionella authority Hydrosense  is calling on cruise lines and holiday operators to prioritise robust water safety management and rapid testing protocols.

Greg Rankin, Hydrosense CEO comments:

"Unfortunately, this latest cruise incident is not an isolated case. Cruise ships pose an elevated risk for Legionella, particularly in facilities such as hot tubs and spas where warm water and complex plumbing systems create favourable conditions for bacterial growth. As we've seen time and again in a number of recent outbreaks, without stringent water management and regular testing the consequences can be serious.

"What's unusual about this latest case is that, so far, testing hasn't actually found any Legionella. At first glance, that might seem reassuring but it's not that simple. Many traditional testing methods used today are outdated, relying on lab cultures that can take up to ten days to return results and, crucially, can miss VBNC bacteria.

"These bacteria are tricky because though they may look dormant during traditional testing they're still alive, still virulent and still capable of causing Legionnaires' disease. So, while its still speculative at this stage the fact is that even though tests on this vessel have come back negative, it could simply be that the bacteria are hiding in a form the test can't detect. In short, a negative result - that is unless using modern, rapid testing methods that can pick up these hidden bacteria - doesn't automatically mean the water is safe."

In 2021 alone, the EU/EEA reported 895 travel-associated Legionella cases - a 38% increase over the previous year - highlighting a growing public health risk as international travel rebounds and climate conditions become increasingly favourable for bacterial growth.

Legionnaires' disease is a potentially fatal lung infection caused by inhaling droplets of water contaminated with Legionella bacteria. The bacteria can be found in a wide range of man-made water systems, including taps, showers, air conditioning units, pools and hot tubs.

Although it is most often associated with "land-based" locations such as large cooling towers, hotels and hospitals, Legionella bacteria can, in fact, be just as big a risk on cruise ships. This is because of the large amount of water on boarding, the complex nature of the storage and distribution systems on board, the number of people using the water facilities and the uncertainty of the source water quality across different destinations.

To help mitigate this risk, Hydrosense  offers rapid, on-site Legionella testing solutions that deliver accurate results within just 25 minutes - allowing cruise operators and their facilities teams to act quickly and prevent potential outbreaks before they occur. Unlike traditional tests, Hydrosense can detect VBNC bacteria, giving a more accurate and timelier picture of water safety before these hidden pathogens have a chance to cause illness or disease.

Greg adds: "When it comes to Legionnaires' disease, prevention is always better than cure. The reality is that current testing practices have not kept pace with the rapidly evolving Legionella risk. Waiting up to ten days for results from a laboratory not only puts guests at unnecessary risk, but this type of testing also fails to detect dormant strains which can still pose a great danger.

"This latest outbreak underscores the urgent need for regular, robust Legionella testing on cruise ships. By implementing rapid, comprehensive testing protocols, operators can better protect passengers and staff, prevent avoidable incidents and safeguard their reputation ahead of what promises to be another record year for cruising."

For information please visit: https://hydrosense-legionella.com/