Quebec City public health authorities are stepping up efforts to determine the source of Legionnaires' disease that has so far claimed 11 lives.
At the same time, officials say they are confident the outbreak is slowing down and under control.
Quebec City's regional public health agency said Sunday it has confirmed 169 cases of legionellosis, of which 11 resulted in death, since the outbreak began in mid-July.
Although there were four more reported cases on Sunday than the day before, François Desbiens – the region's top public health official – said there are clear signs of a slowdown.
"We are seeing a decrease. I'm optimistic about the situation," Dr. Desbiens said in an interview with Radio-Canada's all-news channel.
The Agence de la santé et des services sociaux de la Capitale-Nationale said in a news release Sunday that the most recent cases developed over a period of between 10 and 15 days and are only now appearing because of the delayed incubation period.
The agency said it is moving to expand its inspection and detection efforts in the targeted area, with the outbreak believed to be concentrated in the Quebec City region.
In particular, it said it is launching an epidemiological study in the area using local doctors, nurses and researchers in collaboration with the provincial public health institute.
Authorities have also ordered owners of air-conditioning cooling towers that have so far been inspected – about 30 – to ensure that appropriate levels of chlorine are maintained in the water.
Stagnant water in cooling towers is a common breeding ground for the legionella bacteria, which develops in tiny droplets of water that can then spread into the air.
It has not yet been confirmed that the source of the legionella contamination is in the cooling towers of buildings in the area. Some experts say other potential sources include hot-water systems, where the temperature of pipes can sometimes dip below 50 degrees.
Government inspectors are slated to revisit the 30 towers to make sure full and proper measures are being used. All told, 130 cooling towers are being inspected and cleaned up.
The outbreak is one of the biggest in Quebec's history – the average is two or three cases per year – and politicians stumping for votes in the provincial election campaign have been pointing fingers.
Liberal Health Minister Yves Bolduc criticized the former Parti Québécois government for allegedly failing to implement critical recommendations made in a 1997 report on Legionnaires' disease.
The report proposed that the province's cooling towers and air-conditioning systems be registered and regularly inspected. Last week, Public Security Minister Robert Dutil called for a coroner's inquest into the outbreak.
Meanwhile, Quebec City Mayor Régis Labeaume slammed public health officials for what he said has been a lack of transparency in the management of the crisis.
The Agence de la santé said the average age of the 11 deceased individuals is 77.
Legionellosis can kill up to a third of those infected. Particularly vulnerable are seniors, the very young, smokers and people with fragile immune systems.