OTTAWA, Sept. 3 (Xinhua) -- A deadly seven-week-long outbreak of Legionnaires' disease has claimed 11 lives in Quebec City, the capital of Canada's French-speaking province Quebec, local health authorities announced on Monday.
According to public health officials, the number of infections in Quebec City has also risen to 173 from 158 last Friday. It is believed that the new cases have developed over the last 10 to 15 days due to an incubation period of 2 to 10 days.
The average age of the 11 people who recently died in the outbreak was 77, according to Quebec City's regional public health agency, which hopes to identify the source of the bacteria by mid- September.
The city authorities plan to inspect and disinfect at least 100 rooftop-cooling towers where the deadly bacteria are thought to be passed through air-conditioning systems and be vented outside as mist.
The Quebec provincial government has called for a public inquiry into the outbreak of the non-contagious Legionnaires' disease, which normally affects men, people over the age of 50, smokers, those with a history of heavy drinking, and those with weak immune systems or chronic debilitating illnesses.
Health officials believe that the current outbreak of the disease -- one of the largest in the history of the province that normally sees only two to three cases in an outbreak -- is now under control.
A government-commissioned report released in 2010 found that the number of cases of the disease more than doubled to 51 in 2007 from 24 in 1997, while another report recommended more stringent regulations for building-ventilation maintenance.
Legionnaires' disease is a potentially fatal form of pneumonia known as legionellosis. It acquired its name from the bacterium Legionella pneumophila, which was first identified as the cause of an outbreak of severe pneumonia at an American legionnaires' convention in Philadelphia in July 1976.
Human infection normally occurs through inhaling an aerosol containing Legionella bacteria. Although no vaccine is currently available, the disease can be treated with antibiotics.
According to the World Health Organization, Legionella bacteria are commonly found in lakes, rivers and other bodies of water, and thrive in warm water and warm damp places at between 20 and 50 degrees Celsius. They are also found in man-made facilities such as air-conditioning cooling towers.