Legionnaires' disease
What is Legionnaires' disease?
Legionnaires' disease is a form of pneumonia caused by bacteria of the Legionella type. There are approximately 40 different species of Legionella, but most infections are caused by the species called Legionella pneumophila. The disease is named after a 1976 American Legion Convention in Philadelphia at which a number of attendees became ill with pneumonia.
Legionella bacteria grow in water and are widespread in the environment, being found in lakes, ponds, creeks and other bodies of water.
Legionella can also thrive in man-made systems such as cooling towers associated with air conditioning and spas.
Australia's largest Legionella outbreak occurred in April 2000 at the Melbourne Aquarium where 125 cases of Legionnaires' disease were diagnosed and 4 people died. This outbreak was due to Legionella pneumophila, which was found to be contaminating the Aquarium's cooling towers.
Another species of Legionella, called Legionella longbeachae, is fairly widespread in potting mixes, compost and mulches in Australia and has caused several deaths.
How can you catch Legionnaires' disease?
Legionnaires' disease is caught by breathing in fine droplets of water (aerosols) that contain the bacteria. The disease is not passed from person to person, nor through drinking or washing in water that is contaminated with low numbers of bacteria.
With Legionnaires' disease associated with potting composts, the route of transmission isn't confirmed, but could be by breathing in dusts or aerosols from the potting mix. Legionella longbeachae can survive on unwashed hands for half an hour, so people should wash their hands after potting plants and gardening.
Risk factors for Legionnaires' disease
The disease doesn't affect everyone who comes into contact with the bacteria, but those most at risk are people whose immune systems are compromised in some way. At higher risk are:
- people aged 65 years and over;
- heavy drinkers;
- smokers;
- people with diabetes;
- people with chronic lung diseases; or
- people with a medical condition that impairs the body's defence mechanism, or who are taking drugs that suppress the immune system, for example if you have had a transplant.
Legionnaires' disease symptoms
For several days during the incubation period of the disease, you may feel tired and weak. The incubation period can be between 2 to 14 days after being exposed to the bacteria. A dry cough can be the first sign and most of those admitted to hospital have a high fever. Other signs and symptoms of Legionnaires' disease may include:
- diarrhoea;
- loss of appetite;
- vomiting;
- headaches;
- muscle aches;
- shortness of breath; and
- confusion.
Diagnosis of Legionnaires' disease
Legionnaires' disease is diagnosed through specialised laboratory tests on urine, sputum or blood samples.
Legionnaires' disease treatment
Once diagnosed, there are antibiotics that are highly effective against the bacteria, especially if taken early enough. Antibiotics such as azithromycin, doxycycline or erythromycin may be used.
Unfortunately, at present there is no vaccine available for the prevention of Legionnaires' disease.
How can Legionnaires' disease be avoided?
In Australia there are regulations in place to minimise the growth of Legionella bacteria in public water systems, such as cooling towers. There are also guidelines in place for maintenance of public spas in some States.
Gardeners and other people working with composts or mulches should take some simple precautions.
- Avoid breathing in aerosols and dust from the mix or your hands.
- Wear a mask.
- Wear gardening gloves.
- Moisten the mix to prevent it from creating dust.
- Wash your hands after using potting mix.
Last Reviewed: 25 July 2008
