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Legionnaires' disease

What is Legionnaires' disease?

Legionnaires' disease is a serious,form of pneumonia caused by the legionella bacterium, or Legionella pneumophila.

People become infected when they inhale legionella bacteria from tiny droplets of contaminated water in the air.

Around 10-15% of healthy people who contract Legionnaires’ disease will die from the condition. The number of deaths is likely to be higher among those people with other health problems and elderly people.

Legionnaires' disease is rare in the UK, causing 38 deaths in England and Wales in 2010.

Some strains of the bacteria can also cause a less severe, mild flu-like condition known as Pontiac fever from which patients usually recover without treatment.

Both Legionnaires' disease and the bacterium were discovered following an outbreak in 1976 at a Philadelphia convention of a veterans' association called the American Legion.

How do you get Legionnaires' disease?

You cannot catch the disease from another person who has the infection.

Legionella bacteria are widespread in natural water systems, such as lakes and rivers. However, the conditions are rarely right for people to catch the disease from these sources.

Outbreaks of Legionnaires' disease occur when people are exposed to legionella bacteria in man-made systems where water is held at a high enough temperature - usually between 20C and 45C - for the bacteria to thrive. Examples of these are cooling towers, air conditioning systems, spa pools and hot water systems.

Larger buildings are more susceptible to legionella contamination because they have more complex water systems.

You can catch Legionnaires’ disease by inhaling small droplets of contaminated water suspended as a mist in the air, or by drinking contaminated water.

What are the symptoms of Legionnaires' disease?

The early symptom of the disease is a 'flu-like' illness, with muscle aches, tiredness, headaches and a fever of 38C or more. Sometimes diarrhoea develops and the patient may become confused.

Once the bacteria start to infect the lungs, you may also develop a persistent cough, shortness of breath and chest pains.

Symptoms usually start six to seven days after being exposed to the bacteria.

It is estimated that 10% to 15% of healthy people who develop Legionnaires' disease die from the condition. The number of deaths is likely to be higher among those people with other health problems.

How is Legionnaires' disease diagnosed?

Because the symptoms of Legionnaires' disease resemble flu, it is not always easy to recognise.

If your GP is suspicious that Legionnaires' disease may be behind your symptoms, you will probably be asked whether you have spent time in a building that might have been contaminated, such as a hotel or hospital. You may also be asked whether you have travelled recently, particularly if that involved a stay in a foreign hotel.

Legionnaires' disease can be diagnosed by a urine test that looks for proteins called antigens that are shed by the bacteria.

Your GP will probably also arrange further tests, such as blood tests or a chest X-ray, to assess the effect of the disease on your organs.

How is Legionnaires' disease treated?

Legionnaires' disease is treated with antibiotics that kill the bacteria. These are usually taken in the form of tablets or by intravenous infusion (a drip into a vein) in hospital.

Elderly patients, or people with pre-existing health conditions, are likely to be admitted to hospital.

WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on July 03, 2014

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