A QANTAS employee suffering legionnaires' disease was unlikely to have contracted the potentially deadly infection at Sydney Airport, health authorities said.

The case also appeared to be a one-off, with no evidence of an outbreak of the disease, New South Wales Health's communicable diseases director, Jeremey McAnulty, said.

Qantas employees were notified through a one-page memo, issued yesterday, that a fleet presentation employee, or aircraft cleaner, based at Sydney Airport had contracted legionnaires' disease.

The woman was understood to be in a medically induced coma at Campbelltown Hospital after falling ill on Monday.

A small number of people who work directly with the woman were given health information about legionnaires' disease, the airline said today.

The cleaners were told the Legionella virus could be found in water cooling systems, spa pools, warm water systems and in potting mix and soil.

The Qantas memo also said tests completed on April 19 indicated "there was no Legionellosis bacteria present at Sydney Airport at that time".

"We can confirm that one of our Sydney-based aircraft cleaners has been diagnosed with legionnaires' disease," A Qantas spokesman said today.

"The public health division of the NSW Department of Health has been advised of the case and has indicated that Sydney Airport is highly unlikely to be the source of the bacteria."

Dr McAnulty said there was "no reason to believe that Sydney Airport is the source of the infection".

"As is routine, the local public health unit has investigated potential sources of exposure and there is no particular concern about any location at this point."

But Sydney Airport Corporation (SACL) was today still awaiting the results from the latest tests on its cooling towers, conducted on May 24.

"We are still waiting for the test results," SACL spokesman Peter Vickery said today.

Legionnaires' disease is an acute respiratory infection caused by the bacterium Legionella pneumophila and can cause a broad spectrum of diseases from a mild cough and fever to a serious pneumonia.

But it cannot be spread from person to person, Dr McAnulty stressed.

Meanwhile, the Transport Workers Union (TWU) says it is keeping a close eye on any developments regarding Sydney Airport, as it is concerned for the welfare of the 10,000 people who work there.

"They deserve to know they have absolutely no risk of contracting this disease, considering it is a deadly disease and it's highly contagious through cooling systems if it is present," TWU spokeswoman Fiona Sugden said.