Legionnaires' disease is caused by a bacteria belonging to the Legionella family, Legionella pneumophilia.
It has already infected two women one aged in her 50s and the other in her 70s. They were admitted in the Sydney's Royal North Shore Hospital.
New South Wales (NSW) health officials are investigating an outbreak of Legionnaires' disease.
Both said that they had been to the Chatswood's shopping area. The disease results in an infection in the lungs.
The bacteria Legionella pneumophilia is usually found in water sources such as air conditioning cooling towers, whirlpools, spas and showers.
As a precaution, the Northern Sydney Central Coast Public Health Unit has conducted an inspection of cooling towers in Chatswood.
But it was negative and hence the Director of the Communicable Diseases Branch, Dr Jeremy McAnulty, said that there is no public health risk at Chatswood.
But he promised to continue the monitoring of the situation. The disease usually infects the middle-aged and older people, particularly those with chronic lung disease.
He also said that according to the statistics about 70 cases were reported every year.