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Manchester Port Health Authority
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What is Legionnaires’ disease?

Legionnaires’ disease is a potentially fatal pneumonia caused by Legionella bacteria (Legionella Pneumophila or other Legionella species). There are approximately 200-250 cases of legionella infection annually in the UK, with around 12% of these cases being fatal. Half of these cases are associated with foreign travel, the other half relate to cooling towers and hot & cold water systems in hotels, hospitals, factories, residential homes, ships, spa baths etc. It is therefore essential that the risk of legionnaires’ is controlled on board vessels.

What are the symptoms of Legionnaires’ disease?

The symptoms include flu like illness, followed by a dry cough which frequently progresses to pneumonia. Approximately 30% of people infected have diarrhoea and vomiting and 50% may show signs of mental confusion. The incubation period is between 2 and 10 days.

Who is at risk?

Anyone can become infected with Legionnaires’ disease. Some people however, are more likely to become infected than others. These include:

  • People over 45 years of age;
  • Smokers and heavy drinkers;
  • People with weakened immune systems;
  • People with a chronic disease, and
  • Men are more likely to become infected than women.

Where is legionella found?

Legionella bacteria can be found commonly in natural water sources including rivers and ponds. As they are widespread in the environment, they may contaminate and grow in other systems such as cooling towers, hot and cold water systems and spa pools.

How do you get legionnaires disease?

Infection is caused by breathing in small droplets of contaminated water formed by:

  • Having a shower;
  • Running sink taps;
  • Circulating moist air from air conditioning systems, heating units or humidifiers;
  • Using hoses
  • Washing down the hold

Legionnaires’ disease cannot be contracted by drinking contaminated water or passed from one person to another.

What are the risk factors?

The risk of a person being infected with Legionella depends upon a number of factors. These include:

  • The presence of Legionella bacteria and the strain,
  • Suitable conditions for the multiplication of the bacteria such as: Suitable temperature of between 20oC and 50oC, poor flow, backflow and a source of nutrients such as sludge, scale, rust, algae and other organic matter.
  • A means of creating and spreading inhalable droplets (e.g. aerosol generated by using a tap or a shower),
  • The presence of people who may be infected,
  • The presence of people likely to develop the illness (see ‘Who is at Risk’ above).

What should you do to control the risk?

A risk assessment should be done to assess the risk of exposure to Legionella from water systems on board the vessel. This should include an up-to-date drawing showing the layout of the system; a description of the correct and safe operation of the system, the precautions to be taken and the checks to be completed to ensure the controls are working.

The main objective should be to avoid conditions which allow Legionella to increase and to avoid creating droplets (aerosol). If it is practicable to prevent the risk by replacing a piece of equipment that presents a risk, to one that does not, this should be done.

Practical Measures

Avoid the growth of Legionella by:

  • Maintaining water temperatures between 20oC and 50oC throughout the system. Hot water should be produced or stored at 60oC and distributed so that a temperature of 50oC is achieved at all outlets within 1 minute. Cold water should be below 25oC at all outlets;
  • Removing dead ends or pieces of equipment which are no longer used;
  • Avoiding water stagnation and low flow rates. Stagnation may encourage the growth of biofilm (slimes that form on surfaces in contact with water) which can harbour Legionella and provide conditions which encourage its growth;
  • Avoiding the use of materials in the system which can harbour or provide nutrients for bacteria, e.g. rubber;
  • Keeping the system clean to avoid accumulation of sediments which can harbour bacteria;
  • The use of a suitable water treatment system, and;
  • Ensuring that the system operates safely and is well maintained.

What cleaning and maintenance procedures should be implemented?

The minimum recommended requirements are as follows:

  • The hot water boiler outlet temperature must be warmer than 60oC;
  • Dismantle, inspect, clean and soak shower heads at least once every three months in a disinfectant/chlorine solution. Remove any sediment, algae or calcified deposits found;
  • Locate and eliminate all dead ends which may hold stagnant water.
  • Super-chlorinate the fresh water tanks twice per year and flush the water through all outlet points;
  • Flush any water outlet that is not frequently used on a weekly basis.
  • Have the water tested for Legionella if you find hot and cold water temperatures outside of those recommended.

Further guidance on legionella can be found via: 

  • The Health and Safety Executive (HSE) website or by clicking here. 
  • The European Working Group for Legionella Infections (EWGLI) website or by clicking here.