Legionnaires' disease

10 min read

What is Legionnaires’ disease?

Legionnaires’ disease is a serious lung infection caused by legionella bacteria.

Initial symptoms include a high fever, muscle pain and chills. Once bacteria infect your lungs, you may also develop a persistent cough, chest pains and breathing difficulties.

You should see your doctor if you develop any of the initial symptoms, as they are likely to mean you have an infection of some kind.

If you have serious problems like chest pains and breathing difficulties, seek urgent medical attention.

As the condition has similar symptoms to other illnesses, recent places you have visited will help in making a diagnosis. If it is suspected you have an infection, a urine test can check for Legionnaires' disease.

Read more about

symptoms of Legionnaires' disease
diagnosing Legionnaires' disease

How does Legionnaires’ disease spread?

Legionnaires’ disease is the result of legionella bacteria infecting your lungs.

It is usually caught by breathing in small droplets of contaminated water. It is not contagious and cannot be spread directly from person to person.

Legionella bacteria is commonly found (often in harmlessly low numbers) in sources of water, such as rivers and lakes. However, the bacteria can rapidly multiply if they find their way into artificial water supply systems such as air conditioning systems.

Large buildings, such as hotels, hospitals, museums and office blocks, are more vulnerable to legionella contamination because they have larger, more complex water supply systems in which the bacteria can quickly spread.

Read more about the

causes of Legionnaires’ disease

Treating Legionnaires' disease

Legionnaires' disease is treated with a course of

either taken orally, such as a pill, or through a continuous drip into a vein in your arm.

The length of time you need antibiotic treatment for will depend on the severity of the condition. Treatment usually lasts around a week, but may continue for up to three weeks.

As Legionnaires' disease can be particularly serious in people with pre-existing health conditions, you may be admitted to hospital for a few weeks so your health can be monitored.

Read more about

treating Legionnaires’ disease


Most people make a full recovery from Legionnaires' disease. However, in some cases it can lead to further, life-threatening, problems.

For example, the disease may cause some of your organs, such as your lungs or kidneys to stop working properly. Another complication is

septic shock
, which is the result of a blood infection causing a sudden drop in blood pressure.

An estimated 10-15% of otherwise healthy people who contract Legionnaires’ disease will die due to problems like these.

Can Legionnaires' disease be prevented?

The best way to prevent an outbreak of Legionnaires’ disease is to ensure any water system under your control is properly maintained and conforms to relevant health and safety regulations.

This mainly involves keeping water either cooled below 20ºC or heated above 60ºC. The water supply should also be kept free of any impurities and kept moving so it doesn't stagnate.

Read more about

preventing Legionnaires' disease

Legionnaires’ disease symptoms

The symptoms of Legionnaires’ disease are initially mild, but usually develop into more serious problems associated with pneumonia.

Symptoms can begin any time from two to 19 days after exposure to the initial infection. However, six to seven days is the most common time between getting the infection and the onset of symptoms (known as the incubation period).

Symptoms usually begin with an initial phase that lasts one to two days, in which you experience flu-like symptoms, such as:

  • mild headaches
  • muscle pain

This is followed by more severe symptoms, including:

  • high temperature (fever), usually 38ºC (100.4ºF) or above
  • more severe muscle pain
  • chills
  • tiredness
  • changes to your mental state, such as confusion

Once bacteria begin to infect your lungs, you may also experience symptoms of

, such as:

  • a persistent cough, usually dry at first but as the infection develops you may start coughing up mucus or, rarely, blood
  • shortness of breath
  • chest pains

Some people with Legionnaires’ disease also have symptoms that affect the digestive system, including:

  • feeling sick
  • being sick
  • diarrhoea
  • loss of appetite

When to seek medical advice

If you develop the symptoms above, you should see your doctor as soon as possible. In particular, a high temperature is likely to indicate you have an infection of some kind.

If you experience problems late at night or early in the morning, you may need to use your local out-of-hours service.

If you have more severe symptoms, such as chest pains and breathing difficulties, seek urgent medical attention.

Legionnaires’ disease causes

Legionnaires' disease is caused by an infection of legionella bacteria in your lungs.

You can become infected with legionella bacteria by inhaling droplets of contaminated water in the air, or in rare cases from water that goes down the "wrong way" as you drink.

You cannot develop Legionnaires' disease from simply drinking contaminated water and it does not spread between people.

Legionella bacteria

Legionella bacteria can be found in any freshwater environment - such as rivers and lakes - although it is incredibly rare to become infected from these sources. This is because the bacteria are often only present in low numbers as the temperature of the water is usually too low for the bacteria to grow and spread.

However, if the bacteria manage to find their way into an artificial water system, given the right circumstances, they can quickly grow and reproduce, leading to a widespread contamination of the water system.

The two things that the legionella bacteria require to grow and reproduce are:

  • a water temperature of 20-45ºC (68-113ºF)
  • impurities in the water that the bacteria can use for food, such as rust, sludge, algae and limescale

Water systems known to be vulnerable to legionella contamination include:

  • hot and cold water systems for large buildings, such as hotels and hospitals
  • air conditioning systems that use water for cooling purposes
  • cooling towers

However, any artificial water system is potentially vulnerable to contamination. Although rare in the UK, cases of Legionnaires’ disease have reportedly arisen from contaminated:

  • baths and showers
  • fountains
  • sprinkler systems
  • whirlpool baths
  • spas
  • humidifiers that were being used in food display cabinets

Read about

preventing legionnaires' disease
for information on how to reduce the risk of water contamination.

Increased risk

Everyone is potentially at risk of developing Legionnaires’ disease. However, a number of things make it more likely for certain individuals to experience a more severe form of the infection, including:

  • being 50 years of age or over
  • being a tobacco smoker or having a past history of heavy smoking, although a recent study has shown smoking cannabis may also increase your risk
  • being a heavy drinker
  • having
  • having kidney disease
  • having a weakened immune system (the body’s natural defence against infection and illness) – for example, people with
    HIV and AIDS
  • having cancer, particularly
    lung cancer
    or leukaemia (cancer of the white blood cells)
  • having a pre-existing lung condition, such as
    chronic obstructive pulmonary disease
  • having a heart condition, such as heart failure
  • having a liver condition, such as
    alcoholic liver disease

Legionnaires’ disease diagnosis

See your doctor if you are concerned you have symptoms you think may be the result of Legionnaires’ disease.

You should inform your doctor if you have recently spent time in a building that could be vulnerable to a legionella infection, such as a hotel or hospital.

Also let them know if you have travelled away from home - it is estimated that around a third of Legionnaires’ disease cases diagnosed originated abroad.

This information will be helpful in confirming a diagnosis and possibly allowing health authorities to pinpoint the source of the infection.

Urine test

Legionnaires’ disease can be diagnosed using a urine test. The Legionella bacteria shed proteins called antigens, which can be detected in a urine sample.

If many cases of Legionnaires' disease are suspected, it is possible to get the results of a urine test within a few hours.

Further tests

Further tests, such as a

blood test
or a chest
, may be recommended to assess the effect of the infection on your overall health and on organs, such as your lungs and kidneys.

Notifiable disease

Legionnaires’ disease is a notifiable disease. This means that if a doctor diagnoses the condition, they must tell the local authority. The authority will try to identify the source of the outbreak and put in place any necessary precautionary measures.

Legionnaires’ disease treatment

Legionnaires' disease is usually treated successfully with antibiotics.

Antibiotics are used to kill the bacteria and may include:

  • erythromycin
  • clarithromycin
  • doxycycline
  • azithromycin

These may be taken by mouth as tablets or capsules or may be given through an intravenous infusion. An intravenous infusion is where medicine is given in hospital by a continuous drip through a narrow tube into a vein in your arm.

Depending on the severity of your condition, you will usually need to take antibiotics for 7 to 10 days, although in some cases you may need to take them for up to three weeks.

Side effects

Possible side effects of antibiotics used to treat Legionnaire's disease include:

  • nausea
  • vomiting
  • diarrhoea
  • loss of appetite
  • drowsiness

Vulnerable people

If you are more vulnerable to the effects of Legionnaires’ disease, such as being elderly or having

, it is likely you will be admitted to hospital. This is so the functions of your body can be supported while you recover from the infection.

You may be given oxygen and your breathing will be supported if necessary. You may also be given intravenous fluids (fluids directly into a vein in your arm) to prevent you becoming dehydrated. Your heart rate and blood pressure may also be monitored.


Antibiotic treatment is usually effective in treating Legionnaires' disease. Around 90% of people with the condition make a full recovery.

However, while you may start to feel better after a few days, it can be weeks until you are completely back to normal. During this period, it is common to feel tired.

Legionnaires’ disease prevention

The best way to prevent an outbreak of Legionnaires’ disease is to ensure any water system under your control is properly maintained and conforms to relevant health and safety regulations.

The two most important factors for preventing an outbreak of Legionnaires' disease are:

  • temperature – any water in the system should either be cooled to below 20ºC (68ºF) or heated to above 60ºC (140ºF)
  • hygiene – the water should be kept free of any impurities and never allowed to stagnate (lose its freshness from not moving)

If you are an employer or a private landlord, you have a legal duty to ensure all water systems in your premises are properly operated and maintained to prevent Legionnaires' disease or any other type of water-borne infection.

If you are a homeowner, you are responsible for the water systems in your house. In theory, these could also cause an outbreak of Legionnaires’ disease if they are not properly maintained. However, in practice, the risk is low if you keep your hot water at a high enough temperature and regularly use your water systems (to prevent stagnation).

Travelling abroad

If you are travelling abroad, be aware of the risk of Legionnaires’ disease, and seek medical advice if you develop any

symptoms of Legionnaires' disease

There is currently no vaccine that offers protection against Legionnaires' disease.

At-risk groups

If you are at increased risk of developing severe Legionnaires’ disease – for example, because you have a weakened immune system, you may want to consider avoiding water systems that could be contaminated, such as spas.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.