Frequently asked questions
Legionella, Legionnaires’ disease & the Law

Our FAQs are split into two sections, Legionella & Legionnaire’s disease and Legal obligations. If you have any other questions call our friendly and experienced team on 01673 844 024.

  • FAQs:
    Your legal obligations regarding legionella


    Q: Is there legislation governing legionella management?

    A: You have legal obligations for legionella control under the following legislation:

    • The Health and Safety at Work etc Act 1974 (HSWA)
    • Control of Substances Hazardous to Health Regulations 2002 (COSHH)
    • Management of Health and Safety at Work Regulations 1999 (MHSWR)
    • The Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 (RIDDOR)
    • Notification of Cooling Towers and Evaporative Condensers Regulations 1992
    • The Safety Representatives and Safety Committees Regulations 1977
    • The Health and Safety (consultation with Employees) Regulations 1996

    Q: What do I have to do to comply with my legal duties?

    A: Employers and those with responsibilities for the control of premises should:

    • Identify and assess sources of risk – i.e. conduct a legionellosis risk assessment
    • Prepare an action plan for preventing or controlling the risk (The Written Scheme)
    • Implement, manage and monitor the written scheme – if control measures are to remain effective, then regular monitoring of the systems and the control measures is essential
    • Keep records of the action taken
    • Appoint a person to be managerially responsible


    Q: Specifically what needs to be done to implement a legionella control regime that will ensure I comply with my legal duties?

    A:The Health and Safety Commission’s Approved Code of Practice (ACOP) and Guidance document: Legionnaires’ disease. The control of legionella bacteria in water systems (known as L8) gives practical advice on how to comply with the law. If you follow the advice you will be doing enough to comply with the law in respect of those specific matters on which the ACOP gives advice. You may use alternative methods to those set out in the ACOP in order to comply with the law; however, the ACOP has a special legal status and if you are prosecuted for breach of health and safety law, and it is proved that you did not follow the relevant provisions of the ACOP, you will need to show that you have complied with the law in some other way or a Court will find you at fault. The document also contains guidance issued by the Health and Safety Commission and Executive. Following the guidance is not compulsory and you are free to take other action; but if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to the guidance as illustrating good practice.

    Q: How can I obtain a copy of The Health and Safety Commission’s Approved Code of Practice (ACOP) and Guidance document: Legionnaires’ disease. The control of legionella bacteria in water systems (known as L8)?

    A: Contact HSE Books on 01787 881 165



    What is legionella (legionnaire’s disease)?


    Q: What is Legionnaires’ disease?

    A: Legionnaires’ disease is a potentially fatal form of pneumonia which can affect anybody, but which principally affects those who are susceptible because of age, illness, immunosuppression, smoking etc.

    Q: What causes Legionnaires’ disease?

    A: It is caused by the bacterium Legionella Pneumophila and related bacteria. Legionella bacteria can also cause less serious illnesses which are not fatal or permanently debilitating. The collective term used to cover the group of diseases caused by Legionella bacteria is Legionellosis.

    Q: When was Legionnaires’ disease first identified?

    A: Legionnaires’ disease was first identified following a large outbreak of pneumonia among people who attended an American Legion Convention in Philadelphia in 1976. A previously unrecognised bacterium was isolated from lung tissue samples, which was subsequently named Legionella pneumophila.

    Q: How do people catch Legionnaires’ disease?

    A: It is normally contracted by inhaling legionella bacteria, either in tiny droplets of water (aerosols), or in droplet nuclei (the particles left after the water has evaporated) contaminated with legionella, deep into the lungs. There is evidence that the disease may also be contracted by inhaling legionella bacteria following ingestion of contaminated water by susceptible individuals. Person-to-person spread of the disease has not been documented.

    Q: What are the symptoms?

    A: Initial symptoms of Legionnaires’ disease include high fever, chills, headache and muscle pain. Patients may develop a dry cough and most suffer difficulty with breathing. About one third of patients infected also develop diarrhoea or vomiting and about half become confused or delirious.

    The incubation period is between 2-10 days (usually 3-6 days). Not everyone exposed will develop symptoms of the disease and those that do not develop the `full blown’ disease may only present with a mild flu-like infection.

    Q: How can Legionnaires’ disease be treated?

    A: Legionnaires’ disease can be treated effectively with appropriate antibiotics.

    Q: What are the health risks associated with Legionnaires’ disease?

    A: Infection with Legionella bacteria can be fatal in approximately 12% of reported cases. This rate can be higher in a more susceptible individuals.

    Q: What makes a person more susceptible?

    A: Certain groups of people are known to be at higher risk of contracting Legionnaires’ disease; for example, men appear more susceptible than women, as do those over 45 years of age, smokers, alcoholics, diabetics and those with cancer or chronic respiratory or kidney disease.

    Q: How is Legionnaires’ disease disgnosed?

    A: The disease is usually diagnosed by a combination of tests. The organism may be cultured from the patient’s sputum, bronchial washings or lung tissue. Alternatively, tests are used to measure the presence of antibodies in the blood and, increasingly, tests are available to measure specific antigens in the patient’s urine.

    Q: Can legionella bacteria cause other diseases?

    A: Yes, Legionella bacteria is also responsible for a short feverish form of the illness without pneumonia, known as Pontiac fever. Its incubation period is typically between 2-3 days. Another species of legionella is responsible for a similar form of the illness without pneumonia called Lochgoilhead fever after an outbreak in Lochgoilhead, Scotland. The incubation period can be up to 9 days. A high percentage of those exposed to this agent tend to be affected. However, there have been no recorded deaths associated with either Pontiac or Lochgoilhead fevers.

    To date many species and serogroups of the legionella bacterium have been identified. L. pneumophila causes about 90% of cases, and L. pneumophila serogroup 1 is most commonly associated with cases of Legionnaires’ disease in the UK.

    L. pneumophila serogroup 1 can be further sub-divided to distinguish between strains most commonly associated with Legionnaires’ disease.

    Q: Where does legionella bacteria come from?

    A: Legionella bacteria are common and can be found naturally in environmental water sources such as rivers, lakes and reservoirs, usually in low numbers. Legionella bacteria are not normally dangerous to humans in the low numbers typically found in the environment.

    Q: What environmental conditions affect Legionella bacteria?

    A: Legionella bacteria can survive under a wide variety of environmental conditions and have been found in water at temperatures between 6°C and 60°C. Water temperatures in the range 20°C to 45°C seem to favour growth. The organisms do not appear to multiply below 20°C and will not survive above 60°C.

    They may, however remain dormant in cool water and multiply only when water temperatures reach a suitable level. Temperatures may also influence virulence; legionella bacteria held at 37°C have greater virulence than the same legionella bacteria kept at a temperature below 25°C.

    Q: What environmental conditions do Legionella bacteria require to multiply?

    A: Legionella bacteria require a supply of nutrients to multiply. Sources can include, for example, commonly encountered organisms within the water system itself such as algae, amoebae and other bacteria. The presence of sediment, sludge, scale and other material within the system, together with biofilms, are also thought to play an important role in harbouring and providing favourable conditions in which the Legionella bacteria may grow. A biofilm is a thin layer of micro-organisms which may form a slime on the surfaces in contact with water. Biofilms, sludge and scale can protect Legionella bacteria from temperatures and concentrations of biocide that would otherwise kill or inhibit these organisms if they were freely suspended in the water.