What is Legionella?

Legionella is a naturally occurring bacteria can be found in lakes, rivers etc. When the bacteria enter water systems in the built environment, conditions can often favour and encourage the growth and reproduction to levels which can present risk to get bacterial pneumonia and be fatal to humans. As a result legionella is considered as a biological hazard. This defines the need for a suitable risk assessment to cover water systems in areas mentioned in the regulations.

What is legionellosis?

Legionellosis is the name for a group of illnesses associated with legionella bacteria. There are three main illnesses caused by the bacteria

Legionniares desease

This is a potentially fatal, pneumonia infection that is contracted by breathing in water droplets with an incubation period of 2-10 days with an average onset of 3-6 days. An infectious dose is clearly linked to susceptibility, although it is considered to attack between 2 to 5% of those exposed. The average mortality rate is around  15 and 20% of people infected.

Pontiac Fever

Pontiac fever is a flu like milder illness which usually last up to five days. No treatment is needed for pontiac fever other than paracetamol or ibuprofen for the minor fever and muscle aches. Pontiac Fever is often contracted but goes undiagnosed as the symptoms are so similar to the flu. Pontiac fever does not develop into pneumonia

Lochgoilhead Fever

Loichgoilhead Fever is also caused by legionella bacteria. Like Pontiac fever, loichgoilhead fever is not usually fatal and will normally abate itself without treatment.

The symptoms of Legionnaires’ disease, pontiac fever and loichgoilhead fever are all similar to the symptoms of very severe flu. As a result, legionellosis often goes undetected:

High temperature

Feverishness and chills



Muscle pains




Signs of mental confusionare all some of the symptoms experienced.


Are there different types of legionella bacteria?

Yes, there are more  than 40 different species of legionella bacteria. Legionella pneumophila is the most dangerous as it responsible for about 90% of the cases of infection.   Around 16 different sub-groups of legionella pneumophila have been reported as the cause of infection. Legionella Pneumophila Serogroup 1 is the most associated with Legionnaires’ disease.

What is Pneumonia?

Pneumonia is frequently but not always due to infection that causes inflamation of the lungs. The infection may be bacterial, viral, fungal or parasitic. Symptoms may include fever, chills, cough with sputum production, chest pain, and shortness of breath. Children and babies who develop pneumonia often do not have any specific signs of a chest infection but develop a fever, appear quite ill, and can become lethargic. Elderly people may also have few symptoms with pneumonia. Some cases of pneumonia are contracted by breathing in small droplets that contain the bacteria that can cause pneumonia. These droplets get into the air when a person infected with these germs coughs or sneezes. In other cases, pneumonia is caused when bacteria or viruses that are normally present in the mouth, throat, or nose inadvertently enter the lung. Some types of pneumonia are known as atypical. These include infections caused by certain bacteria, such as Legionella pneumophila, Streptococcus pneumoniae, Mycoplasma pneumoniae and Chlamydophila pneumoniae (this is not an STD). Mycoplasma pneumonia is a common in children and may be associated with non-respiratory problems, such as rashes, anaemia or meningitis.If Pneumonia is diagnosed it is important to find out what form of the infection it could be.

 Who is most susceptible to legionellosis?

The illness occurs more frequently in men than women at a ratio of around 3:1. It is thought that this may be a result of typical occupations, lifestyles and possibly lungs size. However, it usually affects middle-aged or elderly people and individuals with suppressed immune systems. Legionnaires’ disease is very uncommon under the age of 20 and whilst children can catch the disease it is very rare.

What is Legionella pneumophila?

Legionella pneumophila is the type of legionella species responsible for 90% of legionella outbreaks.

How do you get Legionnaires’ disease?

Legionnaires’ disease is contracted by inhaling small water droplets which can be suspended in the air known as aerosols. Aerosols containing the bacteria will pose a risk to susceptible individuals. Infection however, is linked to susceptibility.  Highly susceptible individuals may get infected even at relatively low doses. Domestic water system to be under control if legionella is maintained below 100cfu/l. There are particular controls for the patients of national health services all around the World as they particularly susceptible individuals.

How is Legionniares’ disease treated?

If you were to contract Legionnaires’ disease it would need to be treated with antibiotics. Without treatement it can be fatal. Many antibiotics are highly effective against Legionella bacteria. The two most potent classes of antibiotic are the macrolides and the quinolones. Other agents that have been shown to be effective include tetracycline, doxycycline, and minocycline.

Is Legionnaires’ disease contagious?

Legionnaires’ disease is not contagious and cannot be passed from person to person.

Do I need a risk assessment?

A suitable legionella risk assessment is required to cover water systems.

How often my the legionella risk assessment should be updated?

It should be updated regularly (every two years at least) or when significant changes occur in the water system or the usage of the building.

How often should you review a risk assessment?

An annual review should be conducted to ensure the systems are being suitably managed.

What happens after the legionella risk assessment?

If the legionella risk assessment identifys a low or negligible risk, you may not need to do anything else. However if there is a foreseeable risk of legionella infection then a control scheme will be required to manage the risks.

Will I need to carry out a legionella risk assessment if I have a Health and Safety Risk Assessment?

A good health and safety risk assessment will normally define the requirement for a full legionella risk assessment to be conducted. The health and safety risk assessment will highlight all the likely health and safety risks in the workplace. However, the health and safety risk assessment will not normally actually assess the risks of legionella and it will not provide a site specific control scheme or schematics required. To  provide satisfactury cover, a fully  compliant risk assessment will still be needed.

What do I need to do after the legionella risk assessment is carried out?

If your legionella risk assessment identifies a low or negligible risk, then a simple update of the assessment will be required at least every 2 years. If a reasonably foreseeable risk is identified a programme for continual monitoring and control may be required and remedial actions may also be required to find an engineered solution to manage or eliminate the risk.

How can you control Legionella?

There are numerous measures that can be adopted to create water systems in the built environment that are hostile to the growth of legionella. Most traditionally, temperature is used to control legionella. Wherever possible, temperature should be the initial line of defence used to control legionella growth in water systems.

Temperature control

Cold Water – If we can manage the cold water temperatures throughout the system to ensure that cold water is stored  below 20°C and distributed to all outlets within two minutes of opening the tap below 20°C then the cold water circuit will not encourage bacterial growth including legionella growth.

Hot Water – Hot water should be stored at 60°C and distributed and supplied to all outlets above 50°C preferably within 1 minute of operation.

Stagnation: Stagnation can be prevented by introducing routine flushing programmes and reducing the volumes of stored water.

Chemical control: Chemicals should be used as the last line of defence.  Fundamental measures for control and management of Legionella should be before recommending any chemical treatment programme for commercial or domestic systems.

Will I need to do any routine monitoring?

The control scheme and level of monitoring depends on the water systems and services located on your site. Typically, in a standard building, with a basic domestic water system, a programme of routine temperature checks and annual inspections will be required including by trained individual or expert contractor.

Further to this any infrequently used water services will need to be flushed on at least a weekly basis and any shower heads and spray taps should be cleaned and disinfected on a quarterly basis. Legionella monitoring will not necessary be required, however there are many circumstances where sampling is advocated for examples where temperatures cannot be controlled within the desired range.

Furthermore, legionella sampling will demonstrate that the control scheme is working effectively and will provide responsible personell with documented evidence of the quality of water at their sites.

What temperature should my hot water heater or calorifiers be?

The hot water heater or calorifier water heater is set to achieve a storage temperature of 60°C. Hot water should then be distributed to reach the outlets between 50-55°C preferably within 1 minute of operation.

Temperatures above 55°C will pose a risk of causing scalding injury and should be clearly labelled with caution hot water signs or Thermostaic Mixing Valves (TMVs) should be installed.

What temperatures should my cold water tanks and tap outlets be?

Cold water temperatures should typically be below the recommended 20°C guideline throughout. Cold water temperature should be recorded below 20°C and no more than 3°C rise on the incoming mains supply within two minutes of operation. However, please note that in some circumstances the incoming mains may be greater than 20°C particularly during the summer months of the year.

What do I do if I get a legionella positive result?

If you get a legionella positive result you should not panic! If legionella is identified in your system there are many measures that you can take to eradicate it. Measures such as thermal disinfections, temperature management and chemical disinfections can be used to clean your system. If you obtain a legionella positive result and need assistance or support contact us today.



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