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Legionnaires' disease

This factsheet is for people who have Legionnaires' disease, or who would like information about it.

Legionnaires’ disease is a rare, but severe form of lung infection that is caused by the bacterium Legionella pneumophila.

About Legionnaires' disease

Legionnaires' disease is a severe form of pneumonia. Pneumonia is an infection that causes the small air sacs in your lungs (alveoli) and the tissues around them to become inflamed.

Around 300 to 400 people a year in England and Wales get Legionnaires’ disease, with half of these people catching it abroad. Men are more likely to catch Legionnaires' disease than women. You can't catch it from someone who already has it. Most people get the disease from inhaling the bacterium Legionella pneumophila.

Legionella bacteria also causes Pontiac fever. This is a milder illness than Legionnaires’ disease, which causes flu-like symptoms. Pontiac fever will usually clear up on its own and you won’t need any treatment. However, if you have Legionnaires' disease and don’t receive any treatment, it can be fatal.

Symptoms of Legionnaires' disease

The first symptoms of Legionnaires’ disease usually appear two to 10 days after you have been infected. Early symptoms are similar to those of flu and may include:

  • a high temperature
  • fever and chills
  • a dry cough
  • muscle pains
  • tiredness
  • headaches

If your infection becomes more severe, you may become short of breath, have diarrhoea or feel confused.

These symptoms aren't always caused by Legionnaires’ disease, but if you have them, see your GP as soon as possible.

Complications of Legionnaires' disease

If Legionnaires’ disease is left untreated, it can cause your lungs to fail. This is when there is not enough oxygen passing from your lungs into your blood. Legionnaires’ disease can also cause your kidneys to stop working properly.

Another complication of Legionnaires’ disease is sepsis. This is a severe infection of your whole body because your bloodstream contains high levels of bacteria. You might develop septic shock as a result of sepsis. This causes a large drop in your blood pressure and, as a result, your organs don’t receive enough blood and can’t function properly.

You will be given large amounts of fluid through a drip into a vein in your arm (intravenous infusions) to increase the amount of fluid in your bloodstream and therefore increase your blood pressure. You may also be given medicine, such as dopamine or noradrenaline, to increase the blood flow to your organs. You might also be given oxygen using a mask so your organs have enough oxygen to work properly.

Legionnaires’ disease can be fatal. The sooner you receive treatment, the lower your chances of developing any complications.

Causes of Legionnaires' disease

Legionnaires’ disease is caused by Legionella bacteria, which can be found in natural water sources, such as rivers and lakes, and artificial water sources, such as water towers, hot and cold water systems (for example, air conditioning units) and spa baths (also known as a hot tub or Jacuzzi). This is why you’re more likely to catch Legionnaires’ disease abroad.

Outbreaks of Legionnaires’ disease take place when these water sources become contaminated with Legionella bacteria. Warm temperatures will help the bacteria to grow. You can catch Legionnaires' disease by inhaling aerosols (small droplets of water suspended in the air), which contain the bacteria. About half of all cases of Legionnaires’ disease are associated with travelling abroad. You can also catch Legionnaires' disease if you're in hospital and there is an outbreak.

Anyone can catch Legionnaires' disease, but you’re more likely to get it if:

  • you’re aged 50 or over
  • you smoke
  • you have a weakened immune system (for example, you have HIV/AIDS or are taking medicines that suppress your immune system)
  • you take corticosteroids – a type of steroid usually used to treat inflammation

Diagnosis of Legionnaires' disease

Your GP will ask you about your symptoms and examine you. He or she may also ask you about your medical history, or if you have been abroad recently.

Legionnaires’ disease is diagnosed by a combination of tests. Tests may be done on your sputum (phlegm) or you may be asked to provide a urine sample, which checks for Legionella antigens (substances that cause your immune system to respond to the infection). You may also have a blood test to measure the amount of antibodies in your blood.

You might have an X-ray on your chest to check whether you have an infection in your lungs. You may have to go to hospital to have this done.

Treatment of Legionnaires' disease

If you’re diagnosed with Legionnaires' disease, your GP will prescribe you antibiotics, such as levofloxacin or azithromycin.

The sooner you start your treatment, the less likely you are to develop any serious complications. Always ask your GP for advice and read the patient information leaflet that comes with your medicine.

If your infection is severe or you’re more at risk of complications, you may have to be admitted to hospital and receive your treatment through an intravenous drip.

You will usually start to feel better within three to five days. However, the amount of time it takes to make a full recovery can vary. This may depend on how severe your condition is, how quickly you start treatment and whether you develop any complications.

Produced by Alice Rossiter, Bupa Health Information Team, March 2012.

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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