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Air conditioning units are a potential source of Legionnaires' disease.

Air conditioning units are a potential source of Legionnaires' disease.
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Legionnaires' disease

5-minute read

Key facts

  • Legionnaires' disease is a type of pneumonia caused by legionella bacteria.
  • Legionnaires' disease is life-threatening but is not common
  • There are 2 main types: one is caused by contact with contaminated water, the other is by air-borne bacteria.
  • Legionnaires' disease is generally treated using antibiotics. Some people with Legionnaires’ disease will need to be treated in hospital.
  • It is important that you contact your doctor as soon as possible if you think that you have been exposed to legionella bacteria.

What is Legionnaires' disease?

Legionnaires' disease is an uncommon, severe and sometimes life-threatening form of pneumonia, or lung inflammation, caused by legionella bacteria.

There are many different species of legionella bacteria found in damp environments. The two most common in Australia are legionella pneumophila (found in water) and legionella longbeachae (found in soil). Legionella pneumophila bacteria can contaminate air conditioning cooling towers, decorative fountains, humidifiers, whirlpool spas, shower heads and other bodies of water. Legionella longbeachae can contaminate soil or potting mix.

How is Legionnaires’ disease spread?

You can get infected with Legionnaires’ disease by breathing in contaminated dust or water vapour. You can be exposed to the bacteria at home, at work or in public places.

Legionnaires’ disease is usually not spread from person to person. Outbreaks of Legionnaires’ disease are usually limited to one geographical area, and a single source of infection.

It is important that you contact your doctor as soon as possible if you think that you have been exposed to legionella bacteria.

What are the symptoms of Legionnaires' disease?

Most people with Legionnaires’ disease have no symptoms or a mild illness called Pontiac fever, which rarely causes any complications.

If you do get symptoms, you will most likely start feeling unwell between 2 and 10 days after breathing in the bacteria. Symptoms most commonly develop around 5 to 6 days after exposure. The early symptoms are similar to those of the flu, including:

People with Legionnaires' disease usually get sick between 2 and 10 days after being infected. The symptoms are similar to those of the flu, including:

Sometimes people may go on to develop severe pneumonia.

CHECK YOUR SYMPTOMS — Use the Symptom Checker and find out if you need to seek medical help.

Who is at increased risk of getting Legionnaires’ disease?

You are at higher risk of getting Legionnaires’ disease after exposure to contaminated water systems if you:

  • are a smoker
  • have a chronic illness such as heart disease, lung disease, diabetes, kidney disease, cancer
  • have chronic immune suppression, for example if you take steroid medicines for a health condition
  • are aged over 50 years

How is Legionnaires' disease diagnosed?

Legionnaires' disease is diagnosed in the same way as other forms of pneumonia. Your doctor may listen to your chest with a stethoscope or ask for a chest x-ray. Your doctor may also ask for samples of your mucus, blood or urine.

How is Legionnaires' disease treated?

Legionnaires' disease is generally treated using antibiotics. Some people will need to be treated in hospital.

Can I prevent Legionnaires' disease?

Careful cleaning and maintenance of water systems like air conditioning units, cooling towers, pools, baths and showers can help prevent Legionnaires' disease by reducing the risk that legionella bacteria will grow and be released to the environment.

To prevent contamination with legionella longbeachae that may be in soil and potting mix, follow the manufacturers' warnings on potting mix labels, including:

  • wet the potting mix to reduce the dust
  • wear gloves and a mask
  • wash your hands after handling potting mix or soil

Quit smoking to help reduce your risk, as smoking increases the risk of infection for people exposed to airborne legionella bacteria.

There is no vaccine available against Legionnaires’ disease.


NSW Health (Legionnaires' disease factsheet), SA Health (Legionella pneumophila infection - including symptoms, treatment and prevention), NSW Health (Legionnaires' disease - frequently asked questions), Healthy WA (Legionnaires' disease), Emerging Microbes and Infections (Rolling epidemic of Legionnaires’ disease outbreaks in small geographic areas)

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Last reviewed: May 2022

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