Legionella and Legionnaires Disease

Avoiding confusion, maintaining compliance


Legionella control is an area many find confusing, and often site staff and duty holders do not fully understand their responsibilities. However, the guidance is clear:

“The duty holder should specifically appoint a competent person or persons to take day-to-day responsibility for controlling any identified risk from legionella bacteria. It is important for the appointed person, known as the responsible person, to have sufficient authority, competence and knowledge of the installation to ensure all operational procedures are carried out in a timely and effective manner.” HSG274 Pt 2 Paragraph 17

What Is Legionella?

Legionella is a pathogenic group of gram negative bacteria, which includes Legionella Pneumophila (the bacteria responsible for legionnaires disease).

Around 50 species of legionella have been detected with at least 20 causing illness in humans, however legionella pneumophila is responsible for approximately 90% of cases.

Where does it come from?

Legionella bacteria are widespread in natural bodies of water, such as rivers, lakes, and reservoirs.

Conditions in these locations are rarely conductive to people catching legionellosis from these sources, however this means legionella bacteria can be present in all water supplies. This includes mains water.

Why it’s a problem:

Legionella bacteria can flourish under specific conditions. Unfortunately, those conditions are often present in our water systems.

These include:

  • Ideal Temperatures – Legionella multiplies between 20°C and 50°C with optimum growth occurring at a temperature of 37°C
  • Poor circulation – stagnant water provides an excellent breeding ground for the bacteria
  • Aerosol Production – Water systems which produce aerosols by design, enabling the spread of legionnaires disease.

Who is at risk and how is it transmitted:

Everyone is susceptible to infection. However, certain factors such as age, smoking and existing illnesses can significantly increase the risk.

The bacteria cause illness when they enter and take hold deep within the lungs. For this to happen the bacteria need to be suspended in an aerosol and breathed deep into the lungs. Factors affecting the likelihood of infection include:

  • Droplet Size
  • Concentration of bacteria
  • Duration of exposure
  • Susceptibility of individuals
  • The virulence of strain

What are the symptoms?

Symptoms usually start within 2 – 10 days of exposure. Legionaries Disease is similar to a very severe flu, with symptoms including:

  • Headache, high temperature, feverishness and chills
  • Cough
  • Muscle pains
  • As the illness develops symptoms can become more serious and include:
  • Pneumonia (lung inflammation in which the air sacs fill with pus and may become solid).
  • Diarrhoea and signs of mental confusion.

How serious is it?

About 1 out of every 10 people who get sick with Legionnaires’ disease will die due to complications from their illness.  For those who get Legionnaires’ disease during a stay in a healthcare facility, about 1 out of every 4 will die.

As of 6th September 2017, Public Health England reported that there had been a total of 445 cases of legionnaires disease reported/notified to them since 01 January 2017, with 99 cases occurring in August alone.

Legionella and the Law

Duties under the Health and Safety at Work etc Act 1974 (HSWA) extend to risks from legionella bacteria, which may arise from work activities. More specifically, the Control of Substances Hazardous to Health Regulations 2002 (COSHH) provide a framework of actions designed to assess, prevent or control the risk from bacteria like Legionella and take suitable precautions.

The HSE’s Approved Code of Practice L8 is the main guidance document, referred to in HSWA and COSHH. In addition to ACOP L8 the HSE provides a number of other guidance documents, including:

  • HSG274 – Parts 1 (Evaporative Cooling), 2 (Hot and Cold Water Systems), and 3 (Other Risk Systems)
  • HSG282 – Control of legionella and other infectious agents in spa-pool systems
  • HTM04-01 – Safe water in healthcare premises