A Legionnaires' disease warning has been issued for parts of the University of Sydney's Camperdown campus after three people were admitted to hospital.

Two men in their 60s, and one woman in her 70s, were diagnosed with Legionnaires' disease after separately visiting locations in the area surrounding Victoria Park in the City of Sydney.

NSW Health said all three have been discharged but are warning people who spent time in areas near Victoria Park in Camperdown, including parts of the University of Sydney campus, in the past 10 days to be on alert for symptoms.

Testing found low levels of Legionella bacteria at one cooling tower at the university's Camperdown campus. The tower has been decontaminated and NSW Health has directed others in the area to be disinfected.

Sydney Local Heath District's Dr Isabel Hess said people can be exposed to Legionella bacteria by contaminated water particles from a cooling system.

"Legionnaires' disease is not spread from person to person," she said in a statement on Thursday night.

Symptoms include fever, chills, a cough and shortness of breath and may lead to severe chest infections such as pneumonia.