With one woman in her 90s and a man in his 60s dead, and another 77 confirmed cases, Victoria’s recent incident of Legionnaires disease has become the second largest Australian outbreak on record.
Four Victorians died in Melbourne in April 2000 out of 125 confirmed cases. Here in WA, there are approximately 12 diagnosed cases of Legionella pneumophila each year, with around 60 cases diagnosed as an infection by Legionella longbeachae.
The current case load has been traced backed to a cooling tower in the suburb of Laverton North in west Melbourne, with transmission occurring through the inhalation of contaminated aerosols.
“This gives us increasing confidence that we have identified and already treated the source of this outbreak, and the number of confirmed cases has remained at 77 since the previous update on Sunday,” Victorian chief health officer Clare Looker said at a press conference on Monday afternoon.
“I’m confident that we are now past the peak of the cases associated with this outbreak.”
Nearly all patients diagnosed with a legionella infection will need to be admitted to hospital for treatment and in WA, Legionella (includes Legionella pneumophila) is a notifiable infectious disease.
Any medical practitioner or nurse practitioner attending a patient who has or is suspected to have Legionnaires is required to report the diagnosis to the WA Department of Health under the Public Health Act 2016.
Associate Professor Sanjaya Senanayake, a specialist in Infectious Diseases and Associate Professor of Medicine at the Australian National University explained that as the source of the current outbreak was a cooling tower, the Legionella bacterium could be transmitted as an aerosol for over a kilometre.
Air conditioner cooling towers have been implicated in outbreaks previously, as have aerosol-producing devices such as spa baths/spa pools, water misters and decorative fountains. “Legionella likes living in warm water (25-45°C) such as can be found in cooling towers, which why they require mandatory periodic testing for the presence of Legionella,” he said.
“Two positives about Legionella are that it cannot be transmitted between people, and that commonly used antibiotics are effective against it.”
The disease is more frequently diagnosed in men over 50, particularly smokers or those with underlying health conditions, and globally, the incidence of Legionnaires disease has increased significantly, with notable rises in the US and Hong Kong.
“This increase may be due to a growing number of susceptible individuals, better diagnostic methods, and improved reporting,” Professor Senanayake said.
In many cities, Legionnaires’ disease cases peak during autumn and summer, often following periods of high rainfall and humidity.