Canada's largest city braced itself yesterday for a new outbreak of SARS, on news that an undiagnosed sufferer may have exposed hundreds to the illness that has already killed 24 people here.
Officials were investigating 33 possible SARS cases and had sent some 500 people into quarantine yesterday, less than two weeks after Canada was taken off the World Health Organization (WHO) list of SARS-affected areas.
Canada is the only country outside Asia to report any deaths from SARS, which has killed more than 680 people worldwide since it first appeared in China in November.
The bulk of Canada's outbreak and all of the deaths have occurred around Toronto. An elderly woman brought the illness from Hong Kong in late February.
In recent weeks, the number of active probable SARS cases in Canada had dropped to single digits from a peak of more than 140. Weary health officials had hoped the disease was under control here.
Toronto had not had a new SARS case since April 19 and was cleared by the WHO as a SARS-affected area 12 days ago.
That prompted Toronto hospitals to relax some of their SARS-preventative measures, such as gloves, gowns and visitor restrictions.
But even as Toronto geared up to revive its trampled tourism industry, health officials delivered news of a possible new outbreak on Thursday.
By Friday, five possible SARS cases were under investigation. Health officials refuse so far to classify them as SARS cases because they have no known epidemiological link to any previous case.
On Saturday, officials upped the number to 33 people, including seven health-care workers. They displayed some SARS symptoms: fever, dry cough and difficulty breathing. Three were in critical condition.
"We're treating them as SARS. We're isolating their contacts. We're isolating them in hospital because we're working to wrestle this one down to the ground," said Ontario's commissioner of health, Doctor Colin D'Cunha.
"We are trying to track down every loose end," he said. He asked anyone who has visited any of three area hospitals since April 22 to isolate themselves.
Officials are investigating whether two recently-deceased people had died of SARS without ever having been diagnosed, unwittingly exposing hundreds, including health-care workers, patients and their family members.
One of them, a 96-year-old man, may have developed SARS, rather than a simple pneumonia, after pelvic surgery.
He may have exposed others at North York General Hospital, including a woman who shared his room.
She was transferred to St. John's Rehabilitation Hospital for recovery and is believed to have been the source of four other suspected SARS cases there.
Another patient was transferred to St. Michael's Hospital's neurosurgery unit. It has now been closed along with the other two hospitals.
"We've yet to identify where the breach has been," said Doctor Donald Low, a microbiologist at Mount Sinai Hospital.
Ontario Premier Ernie Eves stressed there was no danger to the general community from these potential new SARS cases.
Low added: "This virus does not do well outside institutional settings where you have close contact."
Barbara Yaffe, Toronto's associate medical officer of health, said that the public health department "has placed approximately 500 under quarantine" and more were expected.
A World Health Organization spokesman said there was no immediate need to re-issue a travel advisory against Toronto that was lifted on April 30.