Legionella infection

Legionella bacteria can cause 2 illnesses in humans:

  • Legionella pneumonia (Legionnaires’ disease) and
  • a mild flu-like illness (Pontiac fever). 

Legionnaires’ disease (legionellosis) is an infection of the lung (pneumonia) caused by the Legionella bacteria.

Exposure to the Legionella bacteria will not necessarily lead to the disease, but the bacteria can cause a type of pneumonia that can be fatal. It can take 2 to 10 days for the symptoms to develop after inhaling the bacteria however symptoms usually appear within 5 to 6 days.

Over the last 5 years, there have been a total of 29 cases of legionellosis reported in the Northern Territory (NT), with around 350 to 500 cases notified nationally each year during this period.

Pontiac fever is not associated with pneumonia or death. Symptoms appear 5 to 66 hours after exposure to the Legionella bacteria, most often between 24 and 48 hours and resolve without treatment.

Where Legionella bacteria comes from

Legionella bacteria are found naturally in low levels in the environment. There are several species of Legionella, but the ones associated with human disease are Legionella pneumophila and Legionella longbeachae.

Legionella pneumophila may be found in environments such as water cooling systems (cooling towers), warm water systems or water heaters, shower heads and spa pools and outdoor fountains. In the absence of effective maintenance and cleaning, high numbers of the bacteria may be found.

Legionella longbeachae occur in potting mix or soils.

The most common way Legionella infection is contracted is by breathing air contaminated with Legionella bacteria. Air is contaminated when aerosols (very fine droplets of water) containing Legionella bacteria are released. The aerosol needs to be very small so that it can penetrate deeply into the lung.  

Evaporative cooling units sometimes used in home air conditioning units have not been known to cause Legionnaires’ disease. Legionnaires’ disease is not transmitted from person to person.


Non-specific ‘flu-like’ symptoms usually occur in the first 24 to 48 hours.

Common symptoms of Legionnaires’ disease include:

  • high temperature (fever)
  • stomach cramps and diarrhoea
  • dry cough or a cough that may produce sputum
  • shortness of breath
  • aches and pains in the muscles
  • chills
  • feeling confused
  • headache
  • feeling tired and loss of appetite.

Not all of the symptoms need to be present for diagnosis. People with these symptoms should see their doctor immediately.

The symptoms of Pontiac fever include:

  • feeling tired and loss of appetite
  • high temperature (fever)
  • chills
  • headache
  • aches and pains in the muscles.

Pontiac fever does not present as pneumonia and has not been associated with death.


Specialised laboratory tests using blood, urine or lung secretions (sputum) are necessary to establish a definite diagnosis of Legionella infections.

Note: Legionnaires’ disease is a notifiable disease under the Notifiable Diseases Act so all cases are reported to the Centre for Disease Control.

Who is most at risk

Those at risk include:

  • older people (aged over 50 years)
  • people with chronic lung disease
  • people with diseases that weaken the immune system such as diabetes and chronic kidney disease
  • people who are taking medications which suppress the immune system, including corticosteroid tablets
  • liver or kidney transplant patients and cancer patients
  • smokers.


Treatment for Legionnaires’ disease is with an antibiotic. For those people with serious symptoms such as severe difficulty in breathing admission to hospital may be required.

People with Pontiac fever generally recover spontaneously within 2 to 5 days and antibiotic treatment is not required. 


Best practice guidelines include regular treatment, cleaning, maintenance and monitoring of water-cooling systems, warm water systems and water storage units performed by the proprietor of a building in accordance with national standards and work health and safety requirements.

An operation and maintenance manual should be kept by the building proprietor and be readily accessible at all times.

People are encouraged to avoid direct inhalation of potting soil or to wear protective coverings over their nose and mouth. People are also encouraged to wash their hands thoroughly after handling potting mix or soil, especially before eating or drinking.


For more information contact your nearest Centre for Disease Control.

Last updated: 12 May 2016

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