A second person has died in Victoria’s worst outbreak of legionnaires’ disease in more than two decades.
The death, of a man in his 60s, follows the death of a woman in her 90s earlier in the week.
According to the state’s chief health officer, there have been 78 confirmed cases since 26 July, though authorities believe the situation is now under control.
But what is legionnaires’ disease, how can you catch it, can it be fatal and what caused this outbreak?
What is legionnaires’ disease?
Legionnaires’ disease – named after an outbreak at a conference of American Legionnaires in 1976 – is a form of pneumonia, or lung infection, caused by legionella bacteria.
The bacteria can be found in damp environments and, in Australia, the two most common types are found in water and soil.
Legionnaires’ disease is a notifiable disease – meaning doctors must tell health authorities if a patient tests positive.
What are the symptoms?
Symptoms include fever, chills, coughing and shortness of breath. Some people may also have muscle aches, headaches, tiredness, loss of appetite and diarrhoea.
Legionnaires’ disease may lead to severe chest infections such as pneumonia. It can also affect the liver, kidneys or heart. Most people recover but the disease is occasionally fatal, according to the Victorian health department.
Richard Bentham, an associate professor from Flinders University, says legionnaires’ disease is fatal for about 10% of people who contract it. However, those who develop the disease are a susceptible subgroup of the general population.
“Most people who are exposed to the bacteria won’t show any symptoms at all, or they [might] show mild symptoms, feel a bit off for a couple of days and get over it,” Bentham says.
Those at highest risk of contracting the disease are smokers, people over 50, those with existing chest or respiratory disease and immunocompromised people.
How do you catch it?
It can be contracted by inhaling contaminated dust or water vapour. Victoria’s health department says the disease is not commonly spread from person-to-person or by drinking contaminated water.
There are only a few cases in the legionella literature regarding possible transmission between people, with the general view being it is not a transmissible disease, Bentham says.
Symptoms can develop up to 10 days from the time of exposure.
What is the source of the Melbourne cluster and what’s being done about it?
Legionella bacteria are often associated with contaminated cooling towers of large buildings. These work to cool buildings by recirculating water through a heat exchanger.
Air comes into the cooling tower from outside – bringing dust and dirt which acts as food for bacteria. Cooling towers operate at about 25C to 30C when warming water.
“So basically the bacteria find themselves in a nutrient-filled incubator,” Bentham says.
Victoria’s health department says a cooling tower in Laverton North, in Melbourne’s west, is the likely source of the outbreak.
The state’s chief health officer, Dr Clare Looker, says the tower is located in a “big site”, noting cooling towers are typically found in workplaces and shopping centres.
Looker says further work will be conducted to determine the amount of legionella in the sample taken from the site.
Since the outbreak emerged on 26 July, the department has visited and disinfected at least 54 sites.
How is legionnaires’ disease treated?
People can be diagnosed with legionnaires’ disease by a urine or sputum test and a chest X-ray. They usually require antibiotic treatment in hospital.
For serious infections, patients may be treated in the intensive care unit and may be placed on a ventilator.
