Health officials on alert for more cases of legionnaires' disease in Sydney's CBD.

Image: ABC

By Michelle Brown

The New South Wales Health Department says there have been no new cases of legionnaires’ disease since four men contracted the illness after visiting a part of Sydney’s CBD.

But NSW Health’s director of communicable diseases Vicky Sheppeard said with an incubation period of two to 10 days, health authorities remained on alert.

It is thought the men contracted the bacterial lung infection by contaminated water, vapour or dust in the Town Hall area.

“It’s just those four people that are associated with being in the city during that incubation period. Our hospitals and doctors are actively looking for any additional cases, should they present,” Dr Sheppeard said.

She said anyone who had been in the Town Hall area who experiences symptoms of the disease should go to their GP.

“It’s a bacterial pneumonia – it starts with fever and chills [a] a quite unwell malaise, aching muscle, headache, a dry cough and short of breath as well,” she said.

Dr Sheppeard said that as of last night the men were “still in hospital, still on treatment”.

All four cases point to an infection zone bounded by Clarence, Pitt, Park and King Streets in Sydney city.

Source of legionnaires infection being studied.

The bacteria that cause legionnaires’ disease live in water and can multiply in the water used to cool air-conditioning systems.

Infection is prevented by routinely maintaining and treating the systems to stop people coming in contact with contaminated water or particles.

Dr Sheppeard said 20 samples had been collected from air-conditioning cooling towers within the likely infection zone, in a bid to identify the source.

She said laboratory testing of the samples would be available in the next four days.

“Today, the field team will also be looking at other sources such as water fountains or other unregulated water sources in that part of the city.”

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This post originally appeared on ABC News.