What is Legionnaires' disease?
Updated: Jun 29
Legionellosis is a collective term for diseases caused by legionella bacteria including the most serious Legionnaires’ disease, as well as the similar but less serious conditions. Legionnaires’ disease is a potentially fatal form of pneumonia and everyone is susceptible to infection. The risk increases with age but some people are at higher risk including:
people over 45 years of age; smokers and heavy drinkers; people suffering from chronic respiratory or kidney disease; diabetes, lung and heart disease; anyone with an impaired immune system.
The bacterium Legionella pneumophila and related bacteria are common in natural water sources such as rivers, lakes and reservoirs, but usually in low numbers. They may also be found in purpose-built water systems such as cooling towers, evaporative condensers, hot and cold water systems and spa pools.
If conditions are favourable, the bacteria may grow increasing the risks of Legionnaires’ disease and it is therefore important to control the risks by introducing appropriate measures.
Where does it come from?
Legionella bacteria are widespread in natural water systems, e.g. rivers and ponds. However, the conditions are rarely right for people to catch the disease from these sources. Outbreaks of the illness occur from exposure to legionella growing in purpose-built systems where water is maintained at a temperature high enough to encourage growth, e.g. cooling towers, evaporative condensers, hot and cold water systems and spa pools used in all sorts of premises (work and domestic).
How do people get it?
People contract Legionnaires’ disease by inhaling small droplets of water (aerosols), suspended in the air, containing the bacteria. Certain conditions increase the risk from legionella if:
the water temperature in all or some parts of the system may be between 20-45 °C, which is suitable for growth
it is possible for breathable water droplets to be created and dispersed e.g. aerosol created by a cooling tower, or water outlets
water is stored and/or re-circulated
there are deposits that can support bacterial growth providing a source of nutrients for the organism e.g. rust, sludge, scale, organic matter and biofilms
What are the symptoms?
The symptoms of Legionnaires' disease are similar to the symptoms of the flu: high temperature, feverishness and chills; cough; muscle pains; headache; and leading on to pneumonia, very occasionally diarrhoea and signs of mental confusion Legionnaires’ disease is not known to spread from person to person.
What you must do
If you are an employer, or someone in control of premises, including landlords, you must understand the health risks associated with legionella. This section can help you to control any risks. Duties under the Health and Safety at Work etc Act 1974 (HSWA) extend to risks from legionella bacteria, which may arise from work activities. The Management of Health and Safety at Work Regulations (MHSWR) provide a broad framework for controlling health and safety at work. 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 Approved Code of Practice: Legionnaires’ disease: The control of Legionella bacteria in water systems (L8) contains practical guidance on how to manage and control the risks in your system. As an employer, or a person in control of the premises, you are responsible for health and safety and need to take the right precautions to reduce the risks of exposure to legionella.
You must understand how to:
identify and assess sources of risk
manage any risks
prevent or control any risks
keep and maintain the correct records
carry out any other duties you may have
Identify and assess sources of risk
Carrying out a risk assessment is your responsibility. You may be competent to carry out the assessment yourself but, if not, you should call on help and advice from either within your own organisation or from outside sources, e.g. consultancies. You or the person responsible for managing risks, need to understand your water systems, the equipment associated with the system such as pumps, heat exchangers, showers etc, and its constituent parts. Identify whether they are likely to create a risk from exposure to legionella, and whether:
the water temperature in all or some parts of the system is between 20–45 °C
water is stored or re-circulated as part of your system
there are sources of nutrients such as rust, sludge, scale, organic matter and biofilms
the conditions are likely to encourage bacteria to multiply
it is possible for water droplets to be produced and, if so, whether they can be dispersed over a wide area, e.g. showers and aerosols from cooling towers
it is likely that any of your employees, residents, visitors etc are more susceptible to infection due to age, illness, a weakened immune system etc and whether they could be exposed to any contaminated water droplets
Your risk assessment should include:
management responsibilities, including the name of the competent person and a description of your system
competence and training of key personnel
any identified potential risk sources
any means of preventing the risk or controls in place to control risks
monitoring, inspection and maintenance procedures
records of the monitoring results and inspection and checks carried out
arrangements to review the risk assessment regularly, particularly when there is reason to suspect it is no longer valid
If you conclude that there is no reasonably foreseeable risk or the risks are low and are being properly managed to comply with the law, your assessment is complete. You may not need to take any further action at this stage, but any existing controls must be maintained and the assessment reviewed regularly in case anything changes in your system.
Managing the risk
As an employer, or person in control of premises, you must appoint someone competent to help you meet your health and safety duties and to take responsibility for controlling any identified risk from exposure to legionella bacteria. A competent person, often known as the responsible person, is someone with sufficient authority, competence, necessary skills, knowledge of the system, and experience. The appointed responsible person could be one, or a combination of:
one or more workers
someone from outside your business
If there are several people responsible for managing risks, e.g. because of shift-work patterns, you must make sure that everyone knows what they are responsible for and how they fit into the overall risk management of the system. If you decide to employ contractors to carry out water treatment or other work, it is still the responsibility of the competent person to ensure that the treatment is carried out to the required standards. Remember, before you employ a contractor, you should be satisfied that they can do the work you want to the standard that you require.
Preventing or controlling the risk
You should first consider whether you can prevent the risk of legionella by looking at the type of water system you need, e.g. identify whether it is possible to replace a wet cooling tower with a dry air-cooled system. The key point is to design, maintain and operate your water services under conditions that prevent or adequately control the growth and multiplication of legionella. If you identify a risk that you are unable to prevent, you must introduce a course of action ie a written control scheme, which will help you to manage the risk from legionella by implementing effective control measures, by describing:
your system, e.g. develop a schematic diagram
who is responsible for carrying out the assessment and managing its implementation
the safe and correct operation of your system
what control methods and other precautions you will be using
what checks will be carried out, and how often will they be carried out, to ensure the controls remain effective
ensure that the release of water spray is properly controlled
avoid water temperatures and conditions that favour the growth of legionella and other micro-organisms
ensure water cannot stagnate anywhere in the system by keeping pipe lengths as short as possible or removing redundant pipework
avoid materials that encourage the growth of legionella (The Water Fittings & Materials Directory link to external website references fittings, materials, and appliances approved for use on the UK Water Supply System by the Water Regulations Advisory Scheme)
keep the system and the water in it clean
treat water to either control the growth of legionella (and other microorganisms) or limit their ability to grow
monitor any control measures applied
keep records of these and other actions taken, such as maintenance or repair work
If you have five or more employees you have to record any significant findings, including those identified as being particularly at risk and the steps taken to prevent or control risks. If you have less than five employees, you do not need to write anything down, although it is useful to keep a written record of what you have done. Records should include details of the:
person or persons responsible for conducting the risk assessment, managing, and implementing the written scheme
significant findings of the risk assessment
written control scheme and details of its implementation
details of the state of operation of the system, i.e. in use/not in use
results of any monitoring inspection, test or check carried out, and the dates
These records should be retained throughout the period for which they remain current and for at least two years after that period. Records kept in accordance with (e) should be retained for at least five years.