Australia is on high alert again after health authorities have discovered a potentially alarming third case of Legionnaire's disease at the Wesley Hospital in the state of Brisbane.

Although showing no signs yet of the potentially fatal disease, a third patient at the hospital has tested positive to the Legionnaires' disease, according to Dr Luis Prado, the hospital's director of medical services. Symptoms of a contraction of the disease include fever, chills, coughing and shortness of breath.

"The patient is showing no symptoms of legionnaires' disease. However, we are starting treatment as a precaution," Dr Prado said in a statement.

"This preliminary test may remain positive for a year and therefore does not indicate when or where the patient contracted the disease."

The male patient, who was accommodated in a different building from the hospital's two earlier confirmed cases, has been a patient since early March, Dr Prado further relayed.

One man, 66-year old John Pearson, has died on June 2 at the Wesley Hospital, while a second patient, a female, remained holed up in intensive care after contracting the disease from the hospital's water system.

A person contracts the dreaded Legionnaires' disease when he or she breathes in contaminated water vapour. Favouring lukewarm water, the Legionella bacteria naturally exists around us.

But with the spread, experts theorized the hospital's airconditioning system could be a factor.

Wesley Hospital continues to restrict its operations, cancelling elective surgeries, refusing new admissions and remaining on emergency bypass.

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