A patient who is being treated for cancer was infected by the dangerous bacteria at a hospital affiliated with the Sherbrooke University Health Centre.
Public health officials say they believe the patient diagnosed with legionnaires' disease was contaminated by the bacteria in her bathroom in the Fleurimont Hospital's oncology wing.
Officials believe the bacteria could have come from the hospital's hot-water system.
Yesterday, hospital staff tested the entire wing for traces of the bacteria and flushed the plumbing system with hot water.
Public health officials say so far, there is no evidence that the disease has spread.
“If the bacteria was in the system for several months it is possible other people caught the disease, and we just didn't make a good diagnosis previously. So we're going to look back in the patient files to examine any cases of pneumonia that were acquired in hospital,” said Mélissa Généreux, director of public health for the Eastern Townships.
Legionnaires' disease is spread through water droplets, not through direct human contact.
Symptoms are similar to pneumonia, causing a high fever, chills, cough, fatigue, muscle pain and loss of appetite.
However, a laboratory test is needed to diagnose the disease.
More than 100 people contracted the disease, and 13 people died during a 2012 outbreak in Quebec City.
Hospital officials in Sherbrooke say the patient who has legionnaires' disease is in intensive care and in stable condition.