TORONTO -- The race to identify a mystery illness that has killed 16 seniors at a Toronto nursing home became a search for its source after public-health officials announced yesterday they are dealing with an outbreak of legionnaires' disease.
 
"A comprehensive environmental investigation has already been begun to identify the source of the bacteria," said David McKeown, Toronto's medical officer of health.
 
"The ventilation system will be shut down for inspection and samples will be taken for analysis."
 
Dr. McKeown said all necessary maintenance and inspections of the ventilation system at Seven Oaks Home for the Aged, which is run by the City of Toronto, had been done as scheduled. He said it is also possible the bacteria originated in the nursing home's water system.
 
"There must have been an environmental contamination, an aerosolization," said Donald Low, medical director of the Ontario Public Health Laboratory. "Aerosolization can occur in showers. We don't know what happened, and that's what, hopefully, the investigation will tell us."
 
Dr. Low added that the bacteria could have been present for quite some time.
 
"What we don't understand is what were the circumstances that allowed this to reach such a critical mass," he said.
 
No residents of the home died yesterday, and for the third day in a row there were no new cases, leading health officials to say they have contained the outbreak. But nearly 40 people remained in hospital.
 
Legionnaires' disease is a rare form of pneumonia that can be fatal in 5 per cent to 30 per cent of cases. It can be contracted only by inhaling water droplets contaminated with legionella bacteria and cannot be spread from person to person.
 
The illness was first identified in 1976, when 34 people died at an American Legion convention in Philadelphia.
 
Symptoms include fever, chills, nausea, muscle ache and malaise, and the disease usually strikes most severely in older people with weakened immune systems. Thirteen cases have been identified in Ontario in the past five years.
 
The breakthrough that allowed officials to identify the sickness yesterday came more than 10 days after the first patient fell ill, and after 40 urine tests for legionnaires' disease came up negative.
 
"In hindsight, it fits," Dr. Low said. "Clinically, it fits. The epidemiology fits. I think we're disappointed the urine test didn't work, and this is something we're going to have to look at and make better. That would have given us the answer [last] Friday. To us, that's unacceptable and we've got to find a better way."
 
Although the illness was not identified until yesterday, Dr. Low said all patients would have been immediately treated with the appropriate antibiotics. The course of treatment will be largely the same now, he said, adding it is just a question of whether the many frail seniors can recover.
 
Although the ventilation and water systems at Seven Oaks nursing home have been shut down, residents not already in hospital will not be removed.
 
Dr. McKeown said moving them would present greater risks and he is confident the measures being put in place will provide sufficient protection.
 
All staff and residents are being given preventive antibiotics and will be monitored through blood tests to identify potential cases of the illness. Many patients improved rapidly when placed on a course of antibiotics.
 
Dr. Low said this may be a new sub-type of the disease, which might explain why it was not identified using the standard urine test.
 
It was only after bacterial cultures taken from autopsy samples were examined in a lab that a positive identification was made.
 
Further tests will be conducted today and tomorrow for confirmation.
 
Toronto Mayor David Miller expressed his condolences to the families affected by the outbreak, and thanked the public-health team for their round-the-clock efforts to identify the illness. He added that a great deal had been learned from the past, but did not refer specifically to Toronto's fatal SARS outbreak in 2003.
 
"The name [legionnaires' disease] might make people nervous, but here's what it means," Mr. Miller said. "This disease cannot be transferred from person to person. There is not, and there never was, a threat to the general population of Toronto."
 
In 2000, a Toronto elementary school was closed after eight teachers and four children fell ill and legionella bacteria were found in the school washroom.
 
One of the deadliest outbreaks occurred in a British hospital in 1985, when 37 people died. Traces of legionella bacteria were found in the air-conditioning system.
 

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