Legionnaires' Disease

Legionella and legionellosis

Legionella are a type of bacteria, some of which can cause disease.

There are over 50 different species of Legionella bacteria. In Australia the most common species that are known to cause human disease are Legionella pneumophila and Legionella longbeachae.

Legionellosis is a collective term for diseases caused by Legionella bacteria including the most serious, Legionnaires’ disease, as well as the less serious condition of Pontiac fever. If a person has a Legionella-related disease and they have pneumonia they have Legionnaires’ disease. If they don’t have pneumonia they may have Pontiac fever which is usually a mild, flu like illness lasting a few days.

Signs and Symptoms: 

The first symptoms of Legionnaires’ disease are non-specific flu-like symptoms including fever, headache and muscle aches. There may also be a mild cough with or without phlegm. Some people may develop diarrhoea, vomiting and abdominal pain. The illness usually progresses rapidly and the chest infection (pneumonia) symptoms become obvious, with high fever, shortness of breath and chest pain being typical symptoms.


It is difficult to distinguish a Legionella infection from other types of pneumonia by symptoms alone and other medical tests are required to diagnose the disease. Such tests include sputum, blood and/or urine tests, which may need to be repeated to confirm the diagnosis.

As the symptoms of Pontiac fever are similar to other common infections, and patients recover in two to three days without treatment, people don't always contact their GP about their illness. It is rarely diagnosed in Australia and so cases are rarely reported.

In all cases, when illness affects a group of people who are connected in some way through environmental exposure to the bacteria, this is regarded as an outbreak requiring rapid and detailed assessment.

Notification requirements

Legionellosis is a notifiable disease under the Queensland Public Health Act 2005, which means laboratories and clinicians are required to report the disease to Queensland Health.

Public Health Unit staff follow up Legionella cases according to communicable disease guidelines. Where it is found that two or more cases may be linked, possible sources of infection are assessed. Under the Work Health and Safety Act 2011, where the cause of a confirmed case of Legionnaires’ disease is work related, the person conducting the business or undertaking must notify Workplace Health and Safety Queensland immediately that an illness arising from the business or undertaking has occurred.

For further information contact your local doctor or nearest public health unit.


A person with Legionnaires’ disease usually needs to be admitted to hospital for appropriate antibiotic treatment and care. Because the progress of the infection can be rapid, it is important that antibiotics be given promptly once the diagnosis is suspected. People who receive early effective treatment usually begin to improve within three to five days. Without early treatment, the illness can progress to severe illness, kidney failure and death.

People with Pontiac fever generally recover spontaneously within 2 to 5 days without treatment.


Legionellosis (infection with the Legionella bacteria) can occur after a person breathes in contaminated water vapour or dust. People may be exposed to the bacteria at home, at work or in public places. Legionellosis is not spread from person to person or from animal to human. Outbreaks occur when susceptible people have a common or shared exposure to an environmental source.

How Legionella longbeachae bacteria are spread remains uncertain but it is thought that the bacteria may be breathed in or could be spread from hand to mouth.

Risk factors

Legionnaires’ disease is relatively uncommon in people under fifty years of age. It is extremely rare in children. People at high risk of serious illness include those over 50 years of age, people who smoke cigarettes and people with a weak immune system e.g. those with a chronic medical condition such as lung disease, kidney disease, diabetes, cancer or HIV.

Incubation period

From the time of infection with Legionella bacteria, it usually takes between two and ten days for symptoms to appear. In most cases symptoms begin between four to six days.


Legionella bacteria are found naturally in the environment and are particularly associated with water, thriving in warm water and warm damp places. They are commonly found in soil, compost and potting mix (Legionella longbeachae) or bodies of water (Legionella pneumophila and other species). Man-made water systems can provide environments that let Legionella bacteria increase to large numbers. These man-made systems include hot or warm water systems, showerheads, spa baths and fountains. Cooling towers associated with air conditioning and industrial cooling processes are also an environment favourable to Legionella bacteria, as are evaporative cooling units sometimes used in home air conditioning. To date however, domestic evaporative air conditioning units have not been proven to cause Legionnaires’ disease.

The critical risk factors for the growth of Legionella bacteria in artificial water systems, such as cooling towers, hot water storage systems and spas, include stagnant water, nutrient availability, poor water quality, and inhalation of contaminated aerosols. Therefore, it is important to regularly clean and disinfect cooling towers (refer to Guide to Legionella control in cooling water systems, including cooling towers (PDF 196 KB) and other sources of aerosols like spas and decorative fountains. To reduce the risk of growth of bacteria such as Legionella, legislation requires that hot water storage systems should be maintained at a temperature of at least 60° Celsius. However, there is increased risk of scalding associated with water temperatures exceeding 50°C.

Warm water systems are typically found in care facilities such as hospitals, early childhood centres, primary and secondary schools, nursing homes for young, aged, sick or disabled persons and other health care facilities. Warm water systems are those that distribute or recirculate water through the majority of the pipe work at a nominal temperature of 45°C. This is achieved by the use of a temperature controlling device, mixing valve or by way of setting the thermostat on an instantaneous or heat exchange heating system. As a consequence, warm water systems require greater maintenance to minimise risks from Legionella.

To avoid exposure to Legionella longbeachae when handling potting mixes and composts, always read the warning on bagged mixes and follow the manufacturer’s instructions. As it is unclear how transmission occurs, avoid inhaling airborne particles such as dust or mists by keeping the mix moist and opening bagged mixes in a well-ventilated space. It is advisable not to touch your face when handling garden mixes and to always appropriately wash your hands, even if gloves have been worn.


Over the ten year period from 2003 to 2012, there were an average of 324 legionellosis notifications per year to State and Territory governments in Australia. In Queensland for the same time period there was an average of 44 legionellosis notifications per year. Notification rates are highest in older people.