What is Legionella?

Legionella is a naturally occurring bacteria wide spread in nature. When the bacteria enters water systems in the built environment, conditions can often favour and encourage significant growth and reproduction to levels which can cause bacterial pneumonia and be fatal to humans. As a result, Legionella is considered as a biological hazard and is listed under the COSHH Regulations. This defines the need for a suitable risk assessment to cover water systems in the work place.

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

  • Legionnaire’s disease
  • Pontiac Fever
  • Lochgoilhead Fever

All types of infection are caused by Legionella pneumophila, although Legionella micdadei is responsible for Lochgoilhead fever.

Legionnaires’ disease is a potentially fatal form of pneumonia caused by the Legionella bacteria. There are actually several pneumonia-like diseases caused by different types of Legionella bacteria, known as Legionellosis.

Some of these are less serious than Legionnaires’ disease, e.g. Pontiac fever, with flu-like symptoms. The primary route of infection is caused by inhaling airborne water droplets that contain Legionella and are small enough to pass deep into the lung.

Legionnaires disease occurs as a result of infections caused by the Legionellaceae family of bacteria. It is a form of pneumonia which results in around 250 identified cases a year and can prove fatal, especially to the elderly or those prone to respiratory problems.

Where is Legionella found?

As Legionella bacteria are commonly found in environmental sources they may eventually colonise manufactured water sources and be found in cooling tower systems, hot and cold water systems and associated water systems which use or store water.

They also require a supply of nutrients to multiply, sources include algae, amoebae and other bacteria. The presence of sludge, sediment, scale and other material within the system, together with biofilms, are also thought to play an important role in harbouring and providing favourable conditions for Legionella bacteria to grow.

How do I get Legionella?

Legionnaires disease is contracted by inhaling small droplets of water suspended in air which contain the legionella bacterium. Legionella bacteria occurs naturally in environmental water sources such as rivers, lakes and reservoirs. The bacteria can survive under a wide variety of environmental conditions and temperatures but seem to favour growth at temperatures between 20°C and 45°C. It cannot be spread from person to person. It is also now believed that the disease can be contracted by inhaling Legionella bacteria following ingestion of contaminated water by susceptible individuals.

How is it treated?

If you were to contract Legionnaires’ disease it would need to be treated with antibiotics. Without treatment 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.

Are there different types

Yes, there are over 40 different species of legionella bacteria. However, Legionella pneumophila is considered the most dangerous as it causes about 90% of the cases of infection. Around 16 different sub groups of legionella pneumophila have been reported as the cause of infection. However, Legionella Pneumophila Serogroup 1 is the most associated with Legionnaires’ disease in the UK.

Who is most Susceptible?

It is impossible to tell who is most at risk just by looking at people, as many conditions that could increase the risk are not visible. Generally speaking though, those who smoke, drink excessively, are overweight and anyone with an underlying illness that affects their immune system may be more at risk.

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.

Everyone is susceptible to infection, but there are those who are at higher risk:

  • Those over 45 years of age
  • Smokers and heavy drinkers
  • The elderly and infirm
  • Those suffering from chronic respiratory or kidney disease
  • Those with impaired immune systems e.g. transplant patients

What are the symptoms?

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

  • High temperature, feverishness and chills
  • Cough
  • Sputum
  • Muscle pains
  • Headache
  • Pneumonia
  • Diarrhoea
  • Signs of mental confusion are all some of the symptoms experienced.

What is the fatality rate of Legionella?

Infection can be fatal in approximately 20% of reported cases. This rate can be higher in a more susceptible population.

A milder form of the disease known as Pontiac fever or Lochgoilhead fever can be contracted by those who have healthier immune systems. These symptoms are typically flu-like and are usually less severe.

Is Legionella contagious?

Legionnaires’ disease is not contagious and cannot be passed from person to person. The disease is transmitted by inhaling the aerosol of an infected water supply, not by infected persons. Legionella is different from Swine Flu and SARS which are contagious.

Your Legal duties

As a person who is responsible for water systems you have certain duties under Health and Safety law. The Health and Safety at Work Act 1974 (HSWA), Control of Substances Hazardous to Health Regulations 1999 (COSHH) and Management of Health and Safety at Work Regulations 1999 (MHSWR) all cite the HSE’s Approved Code of Practice L8 as the recommended guidelines for the management of risk of exposure to Legionella.


  • Identify and assess the risk
  • Appoint a person to be managerially responsible
  • Keep records and ensure effective control

Do I need a Risk Assessment?

A suitable Legionella risk assessment is required to cover water systems in any commercial premise. This includes rented housing stock particularly where communal services are present.

How often is it updated?

The Approved Code of Practice requires that legionella risk assessments be updated regularly (every two years at least) or when significant changes occur that may render the current risk assessment invalid.

Do Landlords need a RA?

In short – The answer is YES – (http://www.hse.gov.uk/services/localgovernment/faq.htm). All local authorities are required to carry out Legionella risk assessments. However the HSE accept a more pragmatic approach and even suggest that a generic risk assessment may be used where large residential housing stocks are involved, however, this will require careful judgement and the Organisation should appoint specialist support to risk categorise stock to create the generic assessments. Further to the risk assessments, annual condition reports will be required to ensure the efficiency of the generic assessments. Various precautionary tasks should also be considered too clearly demonstrate that the risk ratings are appropriate.

Is the landlord or the tenant responsible for managing legionella?

This will ultimately be determined by the lease agreement but generally speaking tenants who have sole occupancy of a building where they are also responsible for maintenance and repairs will be the person or persons on whom the statutory duty falls.

Where there are multiple occupants or where the landlord services and maintains the building, then the duty would usually fall to the landlord unless other arrangements have been documented and communicated.

Do all work places need RA?

The HSC’s, Approved Code of Practice / HSG 274 applies to any undertaking involving a work activity and to premises controlled in connection with a trade, business or commercial enterprise or undertaking. Where water is used or stored which can be transmitted in an aerosol and then be inhaled, there will be a reasonably foreseeable risk of exposure to legionella bacteria. As a result if you have water on your site, you will need to carry out a Legionella risk assessment to identify the level of risk. Ask yourself, does the Health and Safety at work Act apply to your situation? if the answer is yes, then you most definitely need a Legionella risk assessment. Even in a brand new building!

Can Legionella be controlled?

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 a system.

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 within 1 minute of operation.

Chemical control: The use of chemicals can be used as the last line of defence, and we will always explore the fundamental measures for control and management before embarking upon or recommending any chemical treatment programme for domestic systems.

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

To reduce the possibility of increasing the risk of exposure to Legionella bacteria, controls should be introduced which do not allow proliferation of the organisms in the water system and reduce exposure to water droplets and aerosol.

Positive Legionella Results

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. You do not need to report a Legionella positive result to the Environmental Health or your Local Authority. If you obtain a Legionella positive result and need assistance or support contact us today.

When to disinfect CWST's

A domestic cold water storage tank should be cleaned and disinfected when the systems are substantially altered, or after in depth maintenance or when an outbreak has occurred or is suspected. Visual inspection and sampling can also be used as a tool to decide when to clean a cold water storage tank. There is no legislation which defines that you must clean your cold water storage tanks on an annual basis.

However – If the tank is serving drinking water it should be cleaned at least once per year in line with the Drinking Water Inspectorate guidelines see, http://www.dwi.gov.uk/consumer/faq/dws.htm . All tanks should be inspected on at least a six monthly basis. If the tank does not serve drinking water there is no requirement to clean the tank on an annual basis.

What happens when an outbreak of Legionnaires Disease occurs?

An outbreak of Legionnaires’ disease is defined as, a cluster of 2 or more cases exposed to a point source over a short period of time or as a number of apparently sporadic cases over a prolonged period of time in a highly endemic area. Therefore a cluster of 2 or more cases of Legionnaires’ disease linked in time and place is considered the point where epidemiological and environmental investigations are initiated.


Local authorities will have established incident plans to investigate major outbreaks of infectious disease including legionellosis. These are activated by the Proper Officer who invokes an outbreak Committee, whose primary purpose is to protect public health and prevent further infection. This will normally be set up to manage the incident and will involve representatives of all the agencies involved


Do all work places need a legionella risk assessment?

The HSC approved code of practice for Legionella (ACoP L8/ HSG 274) applies to ‘ any undertaking involving a work activity and to premises controlled in connection with a trade, business or other undertaking where water is used or stored and where there is a means of creating and transmitting water droplets which may be inhaled, thereby causing a reasonably foreseeable risk of exposure to Legionella bacteria ‘. In short – if you have water on site that people can be exposed to, you need to assess and manage the risk from Legionella bacteria.

What about domestic property?

The HSC approved code of practice for Legionella (ACoP L8/ HSG 274) is only relevant in circumstances where the Health & Safety at Work etc Act 1974 applies, therefore most domestic property is exempt from regulation. The risk from domestic property is viewed to be very low at this time.

How much does a risk assessment cost?

The cost of a risk assessment is entirely dependent on the amount of water services in use at the property. We offer a free consultancy meeting to assess your needs.

What are the regulations that govern legionella control?

The two main pieces of legislation are the Health & Safety at Work Act (1974) and the Control of Substances Hazardous to Health Regulation (1994). Companies that fail to comply with government guidance may be prosecuted under either of these regulations.