Hamilton public health officials are looking for a possible link among the five legionnaires cases, with the latest person identified last weekend.

A fifth case of Legionnaires' Disease was confirmed after laboratory testing was done, public health officials say. Test results were received late Aug. 23.

"We are still investigating the fifth case," said Rob Hall, direction, health protection of the Public Health services.

He said the investigation will include searching for a possible link between the four previous cases and the fifth case. The investigation includes asking the people to fill out a questionnaire.

Hamilton experienced a Legionnaires outbreak in the summer of 2006 when five cases were reported. Usually, Hamilton has up to three reported Legionnaire cases each year.

In 2006 11 people were reported to have contracted the disease, which killed a 72-year-old Dundas woman that year.

Mr. Hall said the four people previously affected by the disease have been released from hospital. All the people were residents of Hamilton, and are between the ages of 55 and 80.

Part of the investigation includes finding a common point source for the outbreak. Mr. Hall said usually there is a common site that produces the disease.

Sources of exposure include air conditioning systems, hot tubs and spas, and water distribution systems. Proper cleaning and maintenance of these systems will reduce the risk of the disease.

The 2006 investigation led to suspected cooling towers in the downtown area.

Mr. Hall said they have ruled out the downtown area as a possible point source in this latest outbreak.

It is estimated that about 50 per cent of air conditioning units in private and public buildings are known to carry the bacterium, officials say.

Legionnaires' Disease is a severe pneumonia that is commonly found in any aquatic environment. The bacteria can survive for several months in the wet surroundings and multiply in the presence of algae and organic material.

Symptoms of Legionnaires include headaches, muscle pain, high fever, shaking, chills, nausea, vomiting and diarrhea. Doctors say between five to 15 per cent of know cases have been fatal.

"(Legionnaires) is in the environment," said Mr. Hall. "It is opportunistic."

People most vulnerable to the disease are the elderly and people with low immune systems in their high respiratory systems. Also vulnerable are heavy smokers and past smokers, he said.