Outbreak of Legionnaires’ disease in metropolitan Melbourne

What is the issue?

The Department of Health has identified an outbreak of Legionnaires’ disease (also known as Legionellosis) with significant increase in the numbers of cases across multiple locations in metropolitan Melbourne since 26 July 2024. Investigations are underway to identify the source of the outbreak through testing of local cooling towers and other potential sources. Test results indicate that the outbreak is caused by Legionella pneumophilia serogroup 1, which can be detected through a legionella urinary antigen test.

Legionnaires’ disease is caused by Legionella bacteria which are widespread in the environment. Legionella is found in natural bodies of water such as rivers, lakes, creeks and hot springs. It is also found in spas, warm water systems and artificial systems that use water for cooling, heating or industrial processes such as cooling towers, as well as potting mix.

Who is at risk?

Although Legionella bacteria are commonly found in the environment, only a few people who come into contact with the bacteria become infected. In this outbreak, most cases are arising in people who are normally at greater risk of the infection, however, there are also cases in otherwise active and normally healthy adults.

People who are at greater risk of infection include those who:

• are aged over 40 years
• are smokers
• have a chronic lung disease
• have a weakened immune system
• have other underlying medical conditions such as chronic heart, liver or kidney disease, and diabetes.

Symptoms and transmission

Legionnaires’ disease usually presents as a chest infection with symptoms such as fever, chills, cough, headache and muscle aches and pains. Other atypical symptoms may include confusion, nausea, vomiting and diarrhoea. Some people with Legionnaires’ disease may also develop kidney impairment. Legionnaires’ disease can lead to serious illness and cases may require hospitalisation.

Legionnaires' disease is spread by breathing in fine droplets of water that contain Legionella bacteria. It is not commonly spread from person-to-person or by drinking contaminated water.

Recommendations

For the public

• People who live in, work in or have visited metropolitan Melbourne and surrounding areas, and develop symptoms of Legionnaires' disease, should seek urgent medical care.

For clinicians

• Consider Legionnaires’ disease in patients presenting with compatible symptoms who live in, work in or have visited metropolitan Melbourne and surrounding areas.
• If you suspect Legionaires’ disease, request urgent urinary antigen testing through your normal pathology provider. As a priority, order Legionella culture and PCR (e.g. an ‘atypical pneumonia PCR’ panel) on sputum or other respiratory fluid samples (e.g. bronchial washings, endotracheal aspirates). Serology can be requested on blood at symptom onset and 3 to 6 weeks later (as convalescent serology)
• Early diagnosis and treatment with appropriate antibiotics is important. Refer to the current edition of the Therapeutic Guidelines for treatment guidelines or consult with your local infectious diseases service.
• Legionnaires’ disease is an urgent notifiable condition that must be notified to the Department of Health upon initial diagnosis or clinical suspicion as soon as practicable and within 24 hours by calling 1300 651 160 and connecting to the relevant Local Public Health Unit.

For cooling tower operators (in metropolitan Melbourne)

• Operators of cooling towers in the metropolitan Melbourne area are advised to ensure they are up to date with their cooling tower testing, servicing and auditing requirements.