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Legionnaires' disease

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

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.

In 2011, around 230 people in England and Wales had Legionnaires’ disease, with about half of these people catching it abroad. Men are more likely to catch Legionnaires' disease than women. It can affect all ages, but mainly if you’re over 50 years old. You can't catch Legionnaire’s disease from someone who already has it.

Legionella bacteria also causes Pontiac fever. This is a milder illness than Legionnaires’ disease, which causes similar flu-like symptoms, but doesn’t cause pneumonia. If you have Pontiac fever, symptoms occur quicker than Legionnaires’ disease, usually within 12 to 48 hours. Pontiac fever will usually clear up on its own without any treatment. If you find your symptoms aren’t improving, or you’d like more information about Pontiac fever, contact your GP.

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How pneumonia affects the lungs
Pneumonia is an inflammation of the lungs, usually caused by an infection of the lung tissue


  • Symptoms 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 and aches
    • 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, contact your GP as soon as possible.

  • Diagnosis 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 Treatment of Legionnaires' disease

    If you’re diagnosed with Legionnaires' disease, your GP may offer 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 a drip in your arm.

    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 from person to person. This may depend on how severe your condition is, how quickly you start treatment and whether you develop any complications.

    In some cases, you may experience health problems after Legionnaires’ disease. You may have reduced stamina as a result of damage to your lungs, or poor concentration, memory loss and excessive tiredness.

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  • Causes Causes of Legionnaires' disease

    Legionnaires’ disease is caused by Legionella bacteria. The bacteria can be found in natural water sources and artificial or man-made water sources that have been contaminated. This is because some artificial water systems keep water at conditions which encourage the bacteria to grow. Examples of potential sources of Legionella bacteria include:

    • streams, rivers and lakes
    • thermal pools
    • ornamental fountains (that store or recirculate water)
    • humidifiers
    • spa baths and hot tubs (Jacuzzi)
    • ice machines
    • cooling systems (air conditioning units)
    • showers
    • water towers

    Outbreaks of Legionnaires’ disease take place when these water sources become contaminated with Legionella bacteria. Warm temperatures (between 25 and 42 degrees Celsius) help the bacteria to grow quickly. Water that isn’t flowing, or is full of sediment, scale or sludge can also contain bacteria, but it’s the heat that makes the bacteria grow. You can catch Legionnaires' disease by breathing in 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 to warmer countries and from exposure in an aeroplane or hotel. You can also catch Legionnaires' disease if you're in hospital and there is an outbreak.

    Other types of legionella bacteria, such as Legionella longbeachae, can sometimes cause Legionnaires’ disease too. Legionella longbeachae has been associated with breathing in dust or water droplets from compost and potting soil. However the risks are very low, especially if you’re otherwise healthy.

    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
  • Complications Complications of Legionnaires' disease

    If Legionnaires’ disease is left untreated, it can stop your lungs from working properly. If this happens, there won’t be 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 reaction that can happen if you have a bacterial infection which affects your whole body. 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.

    If you have sepsis, you will be given fluids through a drip into a vein in your arm. This can help increase to 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.

  • FAQs FAQs

    Is there a vaccine against Legionnaires' disease?


    No, there's no vaccine against Legionnaires' disease.


    Vaccines work by stimulating your immune system to produce antibodies (proteins that usually fight against bacteria and viruses) in the same way it would to an infection, but you won’t actually become infected with the disease.

    Currently, there is no vaccine available for the prevention of Legionnaires' disease. However, there are certain things you can do to reduce your risk of catching the disease. If you smoke, try to stop – you’re more likely to get Legionnaires’ disease if you’re a smoker. If you’re at an increased risk of getting Legionnaires' disease, for example, you have a weakened immune system (for example, you have HIV/AIDS or are taking medicines that suppress your immune system), don't use a spa bath (also known as a hot tub or Jacuzzi) that hasn't been cleaned or isn’t properly maintained.

    As an employer, what should I be doing to reduce the risk of Legionnaires' disease at my workplace?


    If you’re an employer, you need to follow health and safety guidelines to reduce the risk of Legionnaires’ disease to your employees. These guidelines are set by the Health and Safety Executive (HSE).


    As an employer you must carry out the following to reduce the risk of Legionnaires’ disease to your employees.

    • Identify and assess any sources of risk. This includes checking whether present conditions could help bacteria to grow – for example, checking that the water temperature is correct.
    • Prepare a plan to prevent or control an outbreak of Legionnaires’ disease.
    • Systems should be regularly monitored and a person should be put in charge of the plan.
    • Regularly sampling for the bacteria that causes Legionnaires’ disease is another way to prevent any outbreaks.
    • Keep records of what has been done to reduce the risk.
    • If appropriate, tell your local authority that you have a cooling tower in the workplace.

    Can I get Legionnaires' disease from a spa bath?


    Yes, you can catch Legionnaires’ disease from a spa bath if it’s not properly maintained or cleaned regularly.


    Legionella bacteria are a particular problem in spa baths because the water is kept at a temperature that they can grow in and multiply. Dead skin cells that build up in spa baths from people that use them also provide food for the bacteria. Spa baths should be kept clean and monitored regularly to reduce the risk of an outbreak of Legionnaires’ disease. There are a number of things you can do to keep your spa bath clean, including the following.

    • Disinfectant levels and pH should be tested every two hours.
    • The spa bath should be completely drained and cleaned every week.
    • Filters should be thoroughly cleaned every three months.

    If you have a spa bath, or work somewhere where there is one, the manufacturer of the spa bath will be able to give you more information on how to properly maintain it and keep it clean.

    If you have concerns about whether a spa bath or hot tub has been properly maintained and cleaned, for example if you’re on holiday or in an unfamiliar place, then you may wish to consider avoiding using them.

    How do I know whether I have Pontiac fever or Legionnaires’ disease?


    Pontiac fever is a milder illness than Legionnaires’ disease and you normally won’t need to have any treatment. If you’re getting flu like symptoms or have any concerns, contact your GP.


    Pontiac fever and Legionnaires’ disease are both caused by Legionella bacteria. Pontiac fever is a mild flu-like illness. Symptoms can include headaches, fever and muscle aches, but unlike Legionnaires' disease, you won’t have pneumonia.

    Pontiac fever will usually clear up on its own without any treatment within two to three days. Using antibiotics usually has no benefit, although they may be recommended for more severe symptoms.

    Legionnaires’ disease has similar symptoms, but they are more severe and you will have pneumonia. You may also become short of breath, have diarrhoea or feel confused. You will need to have antibiotics and may have to be treated in hospital.

    These symptoms aren't always caused by Pontiac fever or Legionnaires’ disease, but if you have flu like symptoms, contact your GP as soon as possible.

  • Resources Resources

    Further information


    • Legionnaires' disease. Legionnaires’ disease: frequently asked questions. General information – pontiac fever. Health Protection Agency (Public Health England)., accessed 10 July 2014
    • What is Legionnaires’ disease? Legionella and Legionnaires’ disease: symptoms and treatment. Are there Legionella risks in my workplace? Legionnaires’ disease: what you must do. Health and Safety Executive., accessed 10 July 2014
    • Legionnaires’ disease. Medscape., published 7 May 2014
    • Overview of pneumonia. The Merck Manuals., published September 2013
    • Legionella infections. The Merck Manuals., published March 2014
    • Sepsis and septic shock. The Merck Manuals., published November 2013
    • Legionnaires' disease. National Travel Health Network and Centre., published April 2011
    • Legionnaires' disease in England and Wales: 2011. Naik FC, Zhao H, Harrison T et al. Health Protection Report 2012; 6(44):10−23.
    • Management of spa pools – controlling the risks of infection. Health Protection Agency (Public Health England)., published March 2006
    • Compost and Legionella longbeachae. Health Protection Agency (Public Health England)., published August 2010
    • Van Loenhout JAF, Van Tiel HHMM, Vercoulen JH, et al. Serious long-term health consequences of Q-fever and Legionnaires’s disease. J Infect. 2014 Jun; 68(6): 527−33. doi: 10.1016/j.jinf.2014.01.004
    • Casati S, Gioria-Martinoni A, Gaia V. Commercial potting soils as an alternative infection source of Legionella pnemophila and other Legionella species in Switzerland. Clin Microbiol Infect. 2009 Jun; 15(6): 571−5 doi: 10.1111/j.1469-0691.2009.02742.x
    • Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press., accessed 10 July 2014
    • How vaccines prevent disease. Centers for Disease Control and Prevention., published 8 March 2012
    • Parents guide to child’s immunizations. Centers for Disease Control and Prevention., accessed 18 July 2014
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