Health authorities in Victoria have issued a warning over Legionnaire's disease after four cases of the potentially fatal illness were linked to Melbourne's outer south-east.

The cases have been linked to an area near the Cranbourne shopping centre.

Samples have been taken from several cooling towers that have since been disinfected.

The four people affected are aged between 45 and 78, and all required hospital treatment.

Three of the four have since been discharged.

Victoria's Department of Health and Human Services said it could be up to 10 days before the results from the Cranbourne tower sampling were determined.

People who have been exposed to the potential source could still develop symptoms over the next 10 days.

Anyone suffering flu-like symptoms is urged to contact their doctor.

Victoria's Chief Health Officer Professor Charles Guest said Legionnaires' disease was typically more prevalent at this time of year, when seasons were changing and towers were either activated or deactivated.

Authorities said Legionnaires' disease caused flu-like symptoms, including headache, fever, chills, muscle aches and pains, followed by respiratory problems and pneumonia.

Professor Guest said the four Cranbourne cases had occurred since February.

"People who may be suffering from pneumonia or flu-like symptoms should visit their GP, who will assess and advise on the need for testing for Legionnaires' disease," he said.

Authorities said Legionnaires' disease caused flu-like symptoms including headache, fever, chills, muscle aches and pains, followed by respiratory problems and pneumonia.

Higher risk groups are people aged over 50, heavy smokers, heavy drinkers, people with diabetes or chronic lung disease and those with lowered immunity.

Legionnaires' disease infection is acquired through breathing in very fine droplets of water which contain the bacteria, such as spray drifts which are vented off from a contaminated cooling tower.

Professor Guest said cleaning and decontaminating cooling towers was highly successful in eliminating the risk.

There are between 70 to 80 cases of Legionnaires' disease in Victoria each year.

So far this year 47 people have contracted the illness.