Three men have contracted legionnaires' disease in central Melbourne.
Victoria's health regulator is currently investigating the possibility that there is a link to contaminated cooling towers.
Currently, the focus of the investigation is south of Bourke Street between Queen and Spring streets.
A common source for this outbreak is yet to be determined.
Legionnaires's disease is a bacterial infection which can be airborne and fatal. The bacteria typically occurs in water and soil.
Man-made aquatic environments can become contaminated, such as air-conditioning cooling towers.
"My message to people who have visited the CBD between late January and earlier this month and who may be suffering from pneumonia or flu-like symptoms is to visit their GP who will assess the need for testing for Legionnaires’ disease," Dr Brett Sutton said, reports Nine News.
"The Department is continuing to investigate these cases to seek to identify the possible source of their illness."
So far, 18 cases have been reported to the department in 2018.