NSW Health has confirmed that four people are in hospital being treated for an outbreak of Legionnaires Disease in Sydney.
Health authorities suspect that an infected cooling tower may be responsible for the outbreak of the disease around Town Hall station.
NSW Health is asking anyone who has been in the Town Hall area who experiences symptoms of the disease to go to their GP.
Symptoms include fever, chills, a cough and shortness of breath, NSW Health's director of communicable diseases, Dr Vicky Sheppeard, said.
The department and City of Sydney insprectors have already begun inspections of cooling towers in the CBD.
"Our environmental health officers have been out with the City of Sydney going basically door to door, building by building, inspecting the cooling towers, taking samples and seeing if they can find what might be the source of the infection," Dr Sheppeard said.
"The time from exposure to the onset of symptoms is typically between two and 10 days.
"The bacteria that cause legionnaires' disease live in water and can multiply in the water used to cool air-conditioning systems, so infection is prevented by routine maintenance."
Three of the men infected are aged in their sixties and one is in his 30s. While three of the patients work in the area, one was visiting.
The City of Sydney maintains a register of cooling towers and can order that they be maintained or shut down if sampling finds evidence of Legionnella.
Business owners are expected to have the units inspected every month, cleaned every six months and certified annually.
The City of Sydney released a statement confirming that inspections of the 1400 cooling systems on its register were up to date.
"The City is assisting NSW Health with the investigation and sampling of a number of cooling towers in the city centre," the statement said.
"The City is also providing facilities and resources to enable the operation to be carried out as quickly as possible.
"Any samples will be sent for analysis to a state government-owned laboratory."
Hospitals are required to confidentially notify public health officials of cases of Legionnaires disease in NSW.
Outbreaks of the disease have previously occurred in Sydney in 2011, 1995, 1994, 1993, 1992 and 1989.