What is Legionellosis?

Legionellosis is a collective term for the group of diseases caused by the bacteria Legionella Pneumophila and other bacteria from the Legionelaceae family.

Around 90% of cases of Legionellosis are caused by the bacteria Legionella Pneumophila. Legionella Pneumophila is divided into sixteen different serogroups with L. Pneumophila serogroup 1most often associated with Legionnaires' disease in the United Kingdom.

Legionnaires' disease is a type of pneumonia, named after an outbreak affecting a meeting of the American Legion in Philadelphia in 1976. Although rare, Legionnaires' disease is a very serious infection and is said to be fatal in around 12% of reported cases1.

Pontiac fever is also caused by the L. Pneumophila bacteria and causes a short feverish illness that lacks the pneumonia that is associated with Legionnaires' disease. Legionella Micdadei is responsible for Lochgoilhead fever, a disease also similar to Legionnaires', however to date there have been no recorded deaths caused by either Pontiac Fever of Lochgoilhead fever.

Where can Legionella bacteria be found?

Legionella bacteria are commonly found in low numbers in natural sources of water such as rivers, lakes and reservoirs. Legionella can be found in water systems inside buildings for a number of reasons such as being introduced directly through the mains or through bad hygiene practices.

How is Legionnaires' disease contracted?

Legionnaires' disease may be contracted through inhalation of the aerosol generated by an appliance such as a shower or spa bath or from droplet nuclei. Items of plant such as cooling towers also create an aerosol known as drift that may contain the Legionella bacteria. The risk of infection is increased through increased numbers of bacteria or a decrease in the size of the infected water droplets with droplets less than 5µm penetrating more deeply into the lung.

The risk of contracting Legionnaires' disease increases significantly with people who are more susceptible due to their age, health or if they are immunosuppressed. People who smoke or have chest problems are also more susceptible than the general population.

Why do Legionella cause a problem when found in building water systems?

When found naturally, Legionella bacteria do not usually pose a problem. If they are introduced into a water system in a building, given the right conditions they may multiply and create the potential to infect the building occupants when items such as showers and spa baths are used and generate an aerosol or spray.

What do I need to do to prevent problems associated with Legionella?

People with the responsibility for the management of water systems within buildings must:

• Indentify and assess all sources of risk.
• Prepare a written scheme for preventing or controlling the risk (otherwise known as a log book).
• Carry out the duties that are deemed required by the risk assessment.
• Manage the tasks set out in the Log Book and monitor the systems and their control measures to ensure they remain effective.
• Keep records of all activities carried out and their outcome.
• Appoint a person to be managerially responsible.

(1 Source AcoP Document L8 Legionnaires' disease - The control of Legionella bacteria in water systems.)