Quebec City public health officials say the Legionnaires' Disease outbreak appears to be stabilized and under control.

Now they're trying to find the cause and source.

"This is an exceptional situation," public health director Dr. François Desbiens told a news conference. He said the last major outbreak happened 15 years ago. They believe the problem could be cooling systems of one or two specific high rise buildings, where the bacteria grow in stagnant water and evolving conditions and environment may be a factor.

"We have the same cooling tower (but) the conditions were not there to have the Legionnaire's Disease and the outbreak."

Dr. Isabelle Goupil-Sormany of the public health department said it's taking awhile to locate the source since they are trying to isolate the bacteria.

"We have to treat those samples very carefully in order to let that bacteria grow at its full potential and then we have to analyze those samples," Goupil-Sormany said.

Lab results are expected in mid-October.

Local authorities have cleaned out the systems in over 100 buildings in the Quebec City area.

Eleven people have died of the disease so far with 176 cases reported but no new ones since last Wednesday.