Four people, aged from 45 to 78 years, were recently hospitalised after contracting the pneumonia-like condition.

Three have since been discharged.

Authorities are disinfecting and sampling several towers in the vicinity of Cranbourne Park Shopping Centre on High Street while they search for the source.

There are no cooling towers at the shopping centre.

Victoria's Chief Health Officer, Professor Charles Guest, said the four cases had occurred since February. Professor Guest said the illness is more prevalent at the change of seasons, when towers are either activated or deactivated. "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.

So far this year 47 people have contracted Legionnaires' disease, compared to 28 for the same period last year, according to Health Department data.

In Victoria each year there are between 70 to 80 cases of Legionnaires' disease.

Legionnaires' disease causes flu-like symptoms such as headaches, fever, chills, muscle aches and pains, followed by respiratory problems and possibly pneumonia.

The onset of symptoms can occur up to 10 days after the initial exposure to the bacteria.

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

The bacteria occurs naturally in the environment, mainly in water and soil. It is normally in very low concentrations but can increase dramatically, particularly in man-made aquatic environments with warm re-circulating water, like air conditioning cooling towers.

Legionnaires' disease 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.

Thorough management, decontamination and cleaning of towers is often highly successful in eliminating the risk.

The latest cases follow an outbreak of Legionnaires' disease possibly linked to building cooling towers in Melbourne's CBD last month.

Five people - three men and two women, aged from 51 to 71 years - were hospitalised after contracting the condition. All five have been discharged and are recovering. One of them was put on life support in intensive care.

At the time, authorities disinfected and sampled 92 systems in buildings between Spring and Elizabeth streets in the city's east while they searched for the source.

Three workplaces were linked to the people infected. Authorities identified the other 89 potentially linked water systems by tracing the movements of all five who fell ill.