Researchers say two patients at a Canadian hospital likely contracted legionellosis from the facility’s contaminated hot water system.

An investigation launched after the patients were diagnosed showed a large percentage of water taps in two wings of the hospital were infected with Legionella pneumophila bacteria, as was the energy-conserving heat exchanger used to preheat hot water for one of the wings.

Testing of a sample from the hospital’s hot water system showed it may have been contaminated for 20 years.