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Updated 20 May 2023 | Approved By

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Legionellosis (Legionnaires’ Disease) – Symptoms, Diagnosis and Treatment

Legionnaires' disease (Legionellosis) is a severe form of pneumonia caused by bacteria that live in water. Since the first American outbreak in 1976, there have been many outbreaks worldwide.
  In Australia, there have been several cases of Legionnaires' disease reported every year, with most cases occurring during the summer months. According to the Australian Government Department of Health, around 1.5 in every 100,000 individuals will be diagnosed with the disease [1].
  Knowing the symptoms, diagnosis, and treatment of Legionnaires' disease is essential to prevent severe complications. Seek immediate medical attention from one of our GPs from 24-7 Medcare if you suspect that you may have this condition.

Legionnaires' Disease Symptoms and Signs

Legionnaires' disease can cause various symptoms, which can appear within 2-10 days of exposure to the bacteria. Symptoms may include:
  • Fever
  • Cough, which may be dry or productive
  • Shortness of breath
  • Chest pain
  • Muscle aches
  • Headache
  • Confusion or changes in mental status
  • Gastrointestinal symptoms, such as nausea, vomiting, and diarrhoea
Legionnaires' disease can be severe and potentially life-threatening, especially in older adults, smokers, and people with weakened immune systems. The disease can sometimes cause respiratory failure, septic shock, or kidney failure.

Legionnaires' Disease Cause

Legionnaires' disease is caused by a type of bacteria called Legionella. There are more than 45 types of Legionella. In Australia, there are only seven types that lead to Legionnaires' Disease, especially L. Pneumophila [3]. Legionella bacteria can become aeroborne and then be inhaled into the lungs, where they can cause pneumonia-like symptoms. These bacteria are commonly found in freshwater environments, such as lakes, rivers, and streams. In Australia, they are commonly found in artificial water systems, such as cooling towers, spa baths, and plumbing systems [3].

Is Legionnaires' Disease Contagious?

The disease is usually not contagious and cannot be spread from person to person [4]. This can spread when someone inhales tiny droplets of water from sources such as cooling towers, hot tubs, showers, mist machines, or decorative fountains that are contaminated with the bacteria [5]. Certain factors, such as age, smoking, weakened immune system, and underlying health conditions, can increase the risk of developing Legionnaires' disease. Effective prevention measures, such as regular cleaning and maintenance of water systems, can help reduce the risk of Legionella bacteria growth and infection.

Diagnosis of Legionnaires' disease

Suppose you suspect that you or someone you know may have Legionnaires' disease. In that case, it is essential to seek medical attention immediately. Australian GPs typically diagnose Legionnaires' disease by looking at a combination of the patient's symptoms, medical history, and results from laboratory tests [2]. A diagnosis of Legionnaires' disease is usually made based on a combination of clinical signs and laboratory testing. Early diagnosis and treatment are crucial in preventing serious complications of Legionnaires' disease, such as respiratory failure, septic shock, and organ failure.

Physical examination by a doctor

During a physical examination, the doctor will look for signs of pneumonia, such as a fast heart rate, rapid breathing, and lung crackling sounds. Pneumonia commonly accompanies Legionnaires' disease, including the other symptoms above.

Laboratory tests

Laboratory tests are necessary to confirm the diagnosis of Legionnaires' disease. The most common tests include [2]:
  • Urine antigen test: This test detects a protein produced by Legionella bacteria in the urine.
  • Blood tests: Blood tests can detect antibodies produced by the body in response to Legionella bacteria.
  • Respiratory samples: Samples of sputum or fluid from the lungs may be collected and tested for Legionella bacteria.


Legionnaires' Disease Treatment

Legionnaires' disease is a medical emergency that requires prompt treatment with antibiotics. Early detection and treatment are critical for recovery and a good outcome. Contact your doctor immediately if you suspect you or someone you know may have Legionnaires' disease.


Antibiotics are the primary treatment for Legionnaires' disease [2]. The choice of antibiotic depends on the patient's condition and disease severity. The choice of antibiotics depends on the type of bacteria causing the infection. It may need to be adjusted based on the results of laboratory testing. In severe cases, intravenous antibiotics may be required, and hospitalisation may be necessary.

Supportive care

In addition to antibiotics, patients with severe cases of Legionnaires' disease may require supportive care, such as oxygen therapy or mechanical ventilation, to help with breathing [2]. After treatment, patients are typically monitored closely for any lingering symptoms or signs of relapse. In some cases, additional treatment or follow-up testing may be necessary.

Prevention of Legionnaires' disease

Preventing Legionnaires' disease involves reducing exposure to Legionella bacteria [5]. These include:
  • Wear gloves and face masks when using potting mix and soils
  • Regular cleaning and disinfection of water systems, such as cooling towers, hot tubs, and air conditioning units.
  • Maintaining water systems at appropriate temperatures.
  • Avoiding exposure to water aerosols, such as those generated by hot tubs or decorative fountains.
  • Quitting smoking, as smoking increases the risk of developing Legionnaires' disease.


Complications of Legionnaires' Disease

Legionnaires' disease can be a severe and potentially life-threatening illness; in some cases, it can lead to complications. The complications of Legionnaires' disease may include [2]:
  • Lung damage and failure which can lead to ventilation and other medical support
  • The septic shock is a widespread infection that can lead to organ failure
  • Kidney failure
  • Brain dysfunction leads to confusion, seizures or even coma.
  • Heart complications such as arrhythmias and heart failure.
  • Liver dysfunction
  • Gastrointestinal symptoms
  • Skin rashes
It is essential to seek medical attention promptly if you develop symptoms of Legionnaires' disease, especially if you have a weakened immune system or underlying medical conditions that may increase the risk of complications. Early detection and treatment can help prevent or minimise the risk of complications.


The recovery from Legionnaires' disease can vary depending on the severity of the illness, overall health and how quickly treatment is administered. In general, most people who are diagnosed with Legionnaires' disease recover fully with appropriate treatment. Although those left untreated always worsen after the first, most people feel better within a few days of starting treatment. In the following weeks to months, the symptoms of Legionnaires' should gradually improve [6]. The length of the recovery period can vary from person to person. Some Australians may experience lingering respiratory symptoms, such as shortness of breath or chest discomfort, for several weeks or months after the illness. This is more common in people who have had severe lung damage or who have underlying lung conditions.

Receiving quality care from highly experienced doctors is essential for a prompt diagnosis and receiving the correct medical treatment. With 24-7 MedCare, you can experience telemedicine from the convenience of your own home. Our friendly online doctors will be available 24/7 for a consultation, anytime and anywhere in Australia.

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  1. Waller, C., Freeman, K., Labib, S., & Baird, R. (2022). Epidemiological and clinical characteristics of legionellosis in Northern Australia, 2010–2021. Communicable Diseases Intelligence, 46.
  2. Darby, J., & Buising, K. (2008). Could it be Legionella?. Australian Journal of General Practice, 37(10), 812.
  3. New South Wales Government, Health Protection NSW. (2023). Legionnaires’ disease - frequently asked questions.
  4. Victorian Government Health Information. (2023). Legionellosis (Legionnaires' disease).
  5. Government of Western Australia Department of Health. (2021). Minimising the risk of a Legionella infection at home. HealthyWA.
  6. World Health Organization. (2021). Legionellosis. Fact sheet.