Legionnaires' disease outbreak investigation toolbox

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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 patients may suffer from confusion.

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. 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. Some 5000 cases are reported annually across the EU and EEA/EFTA countries.

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 14 days with a median of 6 to 7 days after exposure.

What is the treatment?

There are specific antibiotics that are effective in 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?

There are 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 investigations are carried out on Legionnaires' disease?

Public Health Departments collect information at the local and national level on all reported cases. Trends or patterns of disease are studied which may show clusters of cases linked to an area of residence or place of work. If an outbreak is detected, local environmental health officers help identify the source of infection and control the outbreak. Information about cases infected across Europe is channelled by Member States through the European surveillance scheme ELDSNet coordinated by the European Centre for Disease Prevention and Control based in Stockholm.