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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

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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 but 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, whirlpool spas, shower heads and other bodies of water. Legionella longbeachae can contaminate soil or potting mix.

People may be exposed to the bacteria at home, at work or in public places. Legionnaires’ disease is not spread from person to person.

It is most commonly contracted by older people, smokers and people who have suppressed immune systems because of medications or illnesses such as cancer, kidney failure, diabetes or HIV.

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?

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:

Within 2 or 3 days other symptoms may also develop, such as:

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. You may be asked to give samples of 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 Legionnaires' disease be prevented?

Careful cleaning of water systems like air conditioning units, cooling towers, pools, baths and showers can help prevent Legionnaires' disease.

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

Smoking increases the risk of infection for people exposed to airborne Legionella bacteria.


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)

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Last reviewed: December 2019

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