Health officials at the Fleurimont Hospital in Sherbrooke have confirmed that a cancer patient has contracted Legionnaires' disease.
The source of the outbreak has been traced to the washroom of the patient's room and that room has been closed.
As a precaution the taps for the sinks and showers have been turned off to the oncology ward, but the toilets are still getting water.
Bottled water, wet wipes and alcohol gel pumps have been distributed to patients and staff.
The process to disinfect the entire water system should be finished later today.
Legionnaire's disease is caused by the bacterium Legionella hemophilia.
It is found in water sources and can only be contracted by inhalation.
People with weakened immune systems are most at risk.