Legionnaires' disease outbreak widens in Melbourne as authorities work to find its source

An outbreak of Legionnaires' disease in metropolitan Melbourne has widened to 40 confirmed cases as authorities continue to trace its source.

A further six are suspected of having the infection, Victoria Health said in today's update.

Since Friday afternoon, health workers across the city have been inundated with dozens of symptomatic patients, most of which have required hospitalisation.

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Some of those had been admitted into intensive care for severe pneumonia.

Victoria Health said tests indicated the cases were caused by Legionella pneumophilia serogroup 1, which can be detected through a legionella urinary antigen test.

Local cooling towers, which are suspected of being the source of the outbreak, are still being investigated and operators are advised to ensure they're up to date with testings.

All 40 confirmed cases so far have been people aged over 40 who reside in or have visited metropolitan Melbourne.

Legionnaires' disease is rare but severe form of bacterial pneumonia.

It can cause a chest infection with symptoms of fever, chills, cough, headache and muscle aches and pains.

Other atypical symptoms may include nausea, vomiting, diarrhoea and confusion.

"Those most at risk are adults aged over 40 years, especially people with other medical conditions or immune compromise, or who smoke," Victoria Health said.

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Victoria Health urged those who live in, work in or have visited metropolitan Melbourne and surrounding areas and develop symptoms to seek urgent medical care.

Healthcare professionals are also encouraged to suspect Legionnaires' disease in patients with compatible symptoms, particularly pneumonia with risk factors.

Legionnaires' disease is caused by its name-sake bacteria, which is widespread in the environment and found in natural bodies of water like rivers and lakes.

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.

The disease is not commonly contracted or spread and is mostly found in people at a greater risk of infection.

Legionnaires' disease is an urgent notifiable condition that requires notification to the Department of Health upon initial diagnosis or clinical suspicion as soon as practicable by calling 1300 651 160 (24/7).