Ten people have died, out of 165 total cases, after contracting Legionnaires' disease in Quebec City, the provincial government said.
Canadian authorities have not publicly pinpointed the exact source of the outbreak. Results from samples may take until mid-September to come in, said Regional Directorate of Health. The agency said it is focusing on places frequented by those afflicted with the disease.
Health authorities are looking especially into cooling systems in two large buildings in Quebec, CNN affiliates CTV and CBC report. A government order has been issued requiring those who own or manage buildings in an unspecified target area to regulate levels of chlorine in the water so that the legionella bacteria -- which cause the disease -- cannot grow.
Quebecois should not have to change their daily habits due to the outbreak, the health department said, noting that healthy people are generally at low risk.
But those who develop tell-tale symptoms are encouraged to contact their doctor, the department said.
Legionnaires' disease is a severe form of pneumonia and is contracted by breathing in small water droplets, whether from mist or vapor, contaminated with the Legionella bacteria. It is not transmitted from person to person.
The disease usually develops two to 14 days after exposure to the bacteria and often begins with a headache, high fever and chills. By the second to third day, a person may develop symptoms of pneumonia like cough, chest pain, and shortness of breath.
Most victims recover, but between 5% and 30% of people who get the disease die, according to the U.S. Centers for Disease Control.
An outbreak of the disease in Philadelphia in 1976, largely among people attending a convention of the American Legion, led to its name.
On Friday, the JW Marriott Chicago hotel announced it removed its lobby fountain and closed parts of its luxury spa after authorities determined them to be the likely source of a Legionnaires' disease outbreak that killed three people.
Health officials in the city confirmed 10 cases of Legionnaires' disease, involving people who visited or stayed at the hotel.