What Is Legionnaires' Disease?

Q - What is Legionnaires' disease?

A - An uncommon form of pneumonia caused by the legionella bacterium. The majority of cases are reported as single (isolated) cases but outbreaks can occur.

Q- What are the symptoms?

A - Early symptoms include a 'flu-like' illness with muscle aches, tiredness, headaches, dry cough and fever. Sometimes diarrhoea occurs and confusion may develop. In rare cases some people may develop symptoms as late as three weeks after exposure.

Q - Who is affected?

A - All ages can be affected but the disease mainly affects people over 50 years of age, and generally men more than women. Smokers and those with compromised immune systems are at a higher risk.

Q - Can you die from it?

A - Deaths occur in 10 to 15% of the general population and may be higher in some groups of patients.

Q - How do you get it?

A - People become infected when they inhale legionella bacteria which have been released into the air in aerosolised form from a contaminated source. Once in the lungs the bacteria multiply and cause either pneumonia or a less serious flu like illness (known as Pontiac fever).

Q - Where do the bacteria live?

A - The bacteria are widely distributed in the environment. They can live in all types of water including both natural sources such as rivers and streams, and artificial water sources such as water towers associated with cooling systems, hot and cold water systems and spa pools. They only become a risk to health when the temperature allows the legionellae to grow rapidly, such as in water systems which are not properly designed, installed and/or maintained.

Q - Can the bacteria be prevented?

A - Control and prevention of the disease is through treatment of the source of the infection, i.e. by treating the contaminated water systems, and good design and maintenance to prevent growth in the first place.

Q - Why is it called Legionnaires' disease?

A - An outbreak of this disease occurred in Philadelphia in 1976, among Legionnaires attending a state convention of the American Legion and led to naming the disease after this group. Subsequently, the bacterium causing the illness was identified and named Legionella pneumophila.

More information on Legionnaires' disease can be found on the Health Protection Agency website and NHS Online.