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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

2-minute read

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 with weakened immune systems.

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

Legionnaires' disease symptoms

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

Within two or three days other symptoms may also develop, such as:

Legionnaires' disease diagnosis

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.

Legionnaires' disease treatment

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

Legionnaires' disease prevention

Legionnaires' disease is not transmitted from person to person. It is usually picked up from water systems like air conditioning units, cooling towers, pools, baths and showers. Careful cleaning of these water systems can help prevent Legionnaires' disease.

For Legionella longbeachae, which can contaminate 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), MyDr (Legionnaires’ disease)

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Last reviewed: November 2017

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