Public health has not found any common links between the four cases of legionnaires' disease reported in Hamilton this month.

However, Dr. Hamidah Meghani, Hamilton's associate medical officer of health, noted that it is usually difficult to pinpoint a particular source of legionella, the bacterium that causes the disease.

"Because it's one of those bacteria that live in warm-weather environment. It's basically all over the place," she told CBC Hamilton.

Since July 10, 4 cases have been confirmed in the Hamilton region. There has also been an increase in legionellosis across the province, with 34 cases reported in Ontario between June 1 and July 12.

Legionnaires' disease is a type of pneumonia, with symptoms of high fever, chills and cough. It is not spread person to person, but rather when a person inhales droplets containing legionella. The majority of people who fall ill are those with chronic illnesses and they are treated with antibiotics.

A variety of sources are potential hosts to legionella, including hot tubs, spas, fountains, showers, plumbing, cooling towers and hot water tanks. There's no evidence, however, that the disease spreads through air conditioning systems.

Although humid weather could exacerbate the growth of the bacterium, Meghani said last week's heat wave was not responsible for the outbreak, as the patients were likely exposed to legionella prior to the extreme weather events.

The disease usually strikes between June and October, so it is "very possible" that more cases will reported in the next few months, Meghani added.