BARRIE -- The health unit is investigating an increase in Legionnaires' disease cases in Barrie.

The Simcoe Muskoka District Health Unit (SMDHU) said there are four recently confirmed cases of the disease in residents.

"It's not uncommon to see cases of Legionnaires' disease in Simcoe Muskoka, however, seeing this number at an unusual time of year for the bacteria, warrants further investigation," said Dr. Charles Gardner, medical officer of health for SMDHU.

Officials said that in the past six years, the health unit has only seen, on average, two cases per year in the city.

They said they believe the risk of the disease spreading is very low. "We have notified health care providers in the community to watch and test for potential cases, and we are looking for a possible source of the bacteria," Gardner said.

Legionnaires' disease is a type of pneumonia commonly found in natural freshwater environments. It can't be contracted from drinking water, or person to person. Legionnaires' disease is developed when inhaling aerosolized water droplets that contain the bacteria.

Symptoms include coughing, shortness of breath, fever, headaches and muscle pain. Other symptoms may develop, like loss of appetite, nausea, vomiting or diarrhea.

Smokers, older adults, and anyone with a compromised lung function are at a higher risk for Legionnaires' disease.

The City of Orillia investigated a Legionnaires' outbreak in October with 10 confirmed cases. Each person who contracted the disease was over the age of fifty and had conditions that put them at risk. The severity of symptoms for each person varied, but some were life-threatening. One person died.

The health unit advises anyone with concerns to call Telehealth Ontario at 1-866-797-0000 or seek immediate medical attention if you have difficulty breathing.