The Health Protection Agency, Centre for Infections, collects information on all reported cases of Legionnaires' disease in residents of England and Wales through its National Surveillance Scheme for Legionnaires' disease.  Annual data are available from 1980. The following fact sheet provides information on the disease, sources of infection, routes of transmission and on symptoms and treatment for infected people.

What is Legionnaires' disease?

Legionnaires' disease is a severe pneumonia caused by the Legionella bacterium.

What are the symptoms?

The range of symptoms include a 'flu-like' illness with muscle aches, tiredness, headache, loss of appetite, dry cough and fever, leading on to pneumonia. Diarrhoea sometimes occurs and confusion may develop.

How serious is the disease and how common is it?

Legionnaires' disease is an uncommon but serious illness and deaths may occur in approximately 10-15% of otherwise healthy individuals.  The number of deaths reported may be higher in some groups of patients, such as those who have weakened immune systems.

Why is it called Legionnaires' disease?

An outbreak of this disease occurred in Philadelphia in 1976, among people (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.

Is this a new disease?

No. Although the Legionella bacterium which causes the disease was identified in 1976, cases have been confirmed as far back as 1947 and some probably also occurred before then.  However since 1976 further species of legionella have been identified in the environment such as Legionella longbeachae, Legionella micdadei or Legionella bozemanii.  A number of these species can occasionally cause Legionnaires' disease.

Can I get the disease from other species of Legionella such as Legionella longbeachae?

In Europe, Legionnaires' disease is most commonly, but not exclusively caused by Legionella pneumophila.  Other species, including Legionella longbeachae, are common in the environment and can cause Legionnaires' disease although such cases are only very rarely reported in Europe.  To put this into context, there have been three community acquired cases of Legionella longbeachea reported in England and Wales over the past ten years, representing only 0.14% of all community acquired cases of Legionnaires' disease identified in England and Wales over the past decade.  However, the occurrence of Legionnaires' disease cases caused by Legionella longbeachae varies across the world and cases associated with this Legionella species are more common in Australia, where they make up nearly half of the Australian cases of Legionnaires' disease.  

How widespread is the disease?

Cases have been reported from all industrialised countries and are increasing in most countries on an annual basis.  Between 400 and 550 cases have been reported in England and Wales in the last couple of years - however, around one third of these cases were infected outside of England and Wales as a result of travel to another country.

Where are legionella bacteria found?

The bacteria are widely distributed in the environment and have been found in rain water, puddles, ponds and rivers.  Problems arise when they contaminate man-made water systems, such as water in air conditioning cooling systems, hot and cold systems in buildings, spa pools and other artificial water systems.

How is Legionnaires' disease acquired?

The infection is not contagious and cannot be caught from another person.  The disease is spread by aerosols (small water droplets that evaporate very quickly) from a contaminated water system.  Breathing in these contaminated aerosols or droplets is the usual route of infection.  Aspiration, where contaminated water gets into the lungs by mistake can be the source of infection in some rare cases.  These cases tend to be associated with infections acquired in hospitals.

Who gets Legionnaires' disease?

All ages can be affected but it mainly affects people over the age of 50 years.  Men are three times more likely to get Legionnaires' disease than women.  Individuals with underlying medical conditions such as heart lung or liver disease - those with impaired immune systems are also at greater risk from the disease.  Smoking is also considered a significant risk factor.

How soon do symptoms occur?

The incubation period can range from 2 to 19 days with a median of 6 to 7 days after exposure.

What is the treatment?

There are specific antibiotics that are effective ain treating the disease.

How is it diagnosed?

A rapid diagnosis can be made by testing a urine sample from the patient, once the relevant symptoms have occurred.

What should I do if I think I have Legionnaires' disease?

If you believe you have this infection, you should tell your doctor so that the appropriate investigations can be started.

How is Legionnaires' disease prevented?

The UK has strict regulations to ensure that water systems used for air cooling or for use in commercial, tourist and other buildings or settings are maintained to standards that minimise risk from the disease and do not harbour the bacteria that cause Legionnaires' disease.    

Concerns have been raised about the link between compost and Legionnaires' disease caused by Legionella longbeachae.  The risk from exposure to this species is likely to be very low for the healthy and younger population but there is insufficient data to properly quantify the extent of the risk that compost and potting soils may pose.  Evidence from Australia suggests that avoiding inhalation of dust or moisture droplets and good standards of personal hygiene when handling compost and soil may reduce the risk of Legionnaires' disease.

What does the HPA do about Legionnaires' disease?

The HPA collects information at the local and national level on all reported cases. It then looks for trends or patterns of disease which may show clusters of cases linked to an area of residence or place of work. If an outbreak is detected it provides advice and assistance to local environmental health officers to help identify the source of infection and control the outbreak.  The HPA also works with clinicians and hospital laboratories in the diagnosis and treatment of cases of Legionnaires' disease.  Information about cases infected abroad is channelled through the European surveillance scheme called the European Centre for Disease Prevention and Control (ECDC) based in Stockholm.