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Ships Are a High Risk for Legionnaires Disease

Posted in Legionnaire's disease on November 11, 2018

Legionnaires is becoming increasingly common these days. It is a severe, and sometimes lethal, form of pneumonia that spreads through water droplets contaminated with Legionella bacteria. Anyone that breathes in contaminated droplets can get the infection. We are currently dealing with a Legionnaires disease outbreak in Washington Heights New York, another two in Illinois, one in Sioux Falls, and one in Rhode Island,  among many other outbreaks that we have dealt this summer. Most commonly associated with hotels, hospitals, elderly homes etc., there is yet another high-risk environment for Legionella that you may never have thought about – ships. Here’s what you need to know about the link between Legionnaires and Ships.

There have been a lot of cases of Legionnaires disease on ships. And the problem is not just constricted to passenger ships. Even general cargo ships have been found to carry the deadly bacteria. Surveys have shown that drinking water and air conditioning in general cargo ships are often contaminated with the Legionella bacteria. Therefore, even ships require proper maintenance and safety requirements just like any other places that are at risk of carrying the bacteria.

About Legionella Bacteria

Legionella is a pathogenic bacteria that causes Legionellosis or better known as Legionnaires disease or Legionnaires pneumonia. Over 90% of the infections caused are due to the strain Legionella pneumophila. Legionellosis can be of both pneumonic and non-pneumonic type. Non-pneumonic form of Legionella cause Pontiac fever, which is an acute, influenza-like illness that lasts for around 2-5 days.

Legionella bacteria are ubiquitous in the environment where they complete their life cycle without ever infecting humans. L.pneumophila is found in natural aquatic environments worldwide. However, the most likely source of the disease are artificial (man-made) water systems that provide a favorable environment to the growth and dissemination of the Legionella bacteria.

The bacteria can thrive at temperatures between 20 to 50 degrees Celsius. They can easily survive and multiply inside the free-living protozoa and within the biofilms that form in the water systems. They can proliferate easily in shower heads, spa pools, piped water distribution systems, and storage tanks on ships.


Legionella can cause illness only when you breathe in tiny water droplets that has the bacteria in them. You can’t get Legionella by drinking contaminated water, unless you aspirate (get water “down the wrong pipe”). It usually can only infect someone through inhalation. Most common sources are cooling towers, hot and cold water systems, pools, whirlpool spas and humidifiers. Legionella is not contagious and will not spread through human-to-human contact.

Why ships are considered to be high-risk environments for Legionellosis?

Water systems on a ship are quite complex. All kinds of systems like water storage, piping, and distribution can provide a perfect breeding ground for bacteria to thrive. Ship movement also increases the chances of surge and back-siphonage. The water that gets loaded can vary in temperature. This poses a risk to ships in tropical regions as they have higher water temperatures, which gives the Legionella bacteria perfect opportunity to survive and grow.

Additionally, proliferation is encouraged due to long-term water storage and stagnation in tanks and pipes. The bacteria can rapidly grow in hot and cold piped water systems which increases the risk of exposure through aerosolization. Not all those who inhale vapor will get sick. Some of them who are more at risk are those who are 50 years or older, those who have history of smoking, people who have lung disease, those with weakened immune systems or any other underlying diseases, like diabetes, asthma, etc.

Lastly, poor potable water quality has also been linked to spread of Legionnaires on ships. There is more growth of Legionella bacteria in systems that have drinking water because of stagnation and also, because they operate in the temperatures ranging from 25℃ to 50℃.

Prevention of Legionella on Ships

There is more awareness about the Legionnaires today. People are far more informed about the risks that the disease carries. This means that people ashore are also becoming familiar with the dangers it can have onboard. Not to mention the significant corporate risk it has with damaging the reputation and integrity of the line, if the outbreak is caused on their vessel. This makes it crucial for the Legionella risk assessment to be included as a part of ship’s safety, repair and maintenance program.

A proper Water Safety Plan (WSP) should be put in place. This should be based on generic set of guidelines but also include individual vessel risk assessment. Staff should be properly trained to implement the safety regulations mentioned in the plan. WHO has a guide to ship sanitation that can be easily included in you generic set of guidelines. The guidelines include everything from storage measures to operational monitoring measures.

In general, the primary measures you should take to prevent a outbreak would be to control the temperature and add biocides so as to keep pathogen numbers to a safe level. Other barriers should be put in place too so as to control the growth of harmful microbes on the ship like:

  • Reducing the residence time of stored water at all locations
  • Keeping water temperatures above or below the optimal growth condition for the bacteria. Since bacteria thrives between 20℃ and 50℃, it is important to keep all the cold water systems below 20℃ and hot water systems above 50℃.
  • Biocides should be actively put in place with a reliable, well designed and properly placed dosing systems.
  • Minimizing the opportunity for aerosol generation and inhalation

The control measures should focus on prevention of contamination, proper disinfection, maintaining water systems, avoiding stagnant water systems for too long, avoidance of dead ends in pipes and regular cleaning of water systems especially recreational water environments. Training the staff is also quite important to prevent the spread of disease.

Additionally, people should be made aware about the disease. If you have a passenger ship liner, then inform travelers, so if they experience any such symptoms they are able to promptly act upon it. There should be more public, scientific and medical awareness around the symptoms and causes of the Legionella infection. This will help in better reporting of the cases.

Shipowners should be able to protect themselves from any Legionella queries they receive from passengers by maintaining a proper water management system put in place. Despite the unpredictability, there is still room for vessel owners to create a plan that successfully omits out the risk of Legionella from their ships.

By: Pooja Sharma, Contributing Writer (Non-Lawyer)