Just two weeks ago, Toronto health officials were so convinced they had beaten SARS into submission that they dismantled key elements of their containment team while lead members took off on international tours to describe how the city defeated the disease.
Ontario commissioner of public security James Young, Toronto associate medical officer of health Bonnie Henry and two other medical experts flew to the SARS-embattled regions of Hong Kong, Beijing and Taipei to share the Toronto experience.
Mount Sinai Hospital's chief microbiologist, Donald Low, jetted off to give weekend lectures in Glasgow, New York and Washington, as Andrew Simor, head microbiologist at Sunnybrook and Women's College Health Sciences Centre, left on a much-needed vacation. Toronto's medical officer of health, Sheela Basrur, flew to Jamaica for a rest before West Nile season hits.
Meanwhile, epidemiologist Ian Johnson, who had been seconded by Ontario's Ministry of Health from the University of Toronto to track the disease, returned to the classroom: "I thought it was over," Dr. Johnson said. "Everyone thought it was over."
But on Friday morning, Dr. Low found himself behind a table at North York General Hospital, assessing file after file of previously unrecognized cases, and he realized how wrong they had been.
"Holy Christ," he thought.
Dr. Low and staff from Toronto public health had expected to review patient files and identify the root of a small new cluster within a couple of hours. Instead, they uncovered a trail of deadly and serious cases dating back weeks.
"We were there until midnight," Dr. Low said.
How had they missed it? Was it inevitable that a sneaky disease that looks like so many other pneumonias would go undetected in the midst of a large outbreak? Had a low-grade chain of transmission simply slipped beneath their radar?
Whatever the answers, a nagging suspicion remains that the oversight was compounded by a dire, patriotic urge to prove to the rest of the world that Toronto was free of severe acute respiratory syndrome.
Faced with the World Health Organization's costly declaration on April 23 that Toronto was too dangerous to visit, politicians, health officials and even the news media quickly banded together against a common enemy - and it was not the virus but WHO, the United Nations agency, that had effectively put Canada's largest city under quarantine.
"That week, that advisory definitely changed our psychology and the way we looked at this [outbreak]" Dr. Low said. "I remember . . . we were putting such a positive spin on things, including myself - everybody wanted to be clean of this."
Now Toronto is holding its collective breath through a crucial weekend once again, as health officials cling to hopes of containment even as the numbers of cases and people in quarantine climb.
The WHO lifted its travel advisory on April 30. Two weeks later, after the agency removed Toronto from its list of SARS-affected areas, Ontario lifted the provincial emergency status. Behind the scenes, the province disbanded members of its epidemiology team and scaled back its emergency-operations centre to a routine monitoring function.
With no known new cases after 20 days, the city had laid down its gloves. On May 16, health staff in area hospitals were instructed that they no longer needed to wear full protective gear.
May 16 is emblazoned with regret in Dr. Low's mind: "As soon as the masks and the gloves came off, you can see this dramatic spike in the cases."
He now heads the painstaking task of retracing steps and searching for the specific link that would connect the troubling new cases of SARS to the original outbreak cluster everyone thought had been conquered.
Toronto public-health staff called Dr. Low at his Mount Sinai office on the evening of May 22, just as he was heading home. Earlier that day he had returned from Ottawa, where he had given yet another talk on Toronto's successful battle against SARS.
There was a new cluster, they told him, centring on patients who had spent time at St. John's Rehabilitation Centre in the city's north end before being transferred to four other Toronto area hospitals.
Contact tracing had turned up no epidemiological link to the first outbreak. But a lab test confirmed that one of the four known patients carried the SARS coronavirus deep in his bronchial tract.
It was back.
Dr. Low's head spun with disbelief. "You're hearing it all and you're trying to minimize it. You're thinking, 'No this can't be right, this can't be.' "
Early indications suggested that the cluster originated with a patient transferred from North York General or with a woman who had recently travelled in South China, then visited her ailing son at St. John's.
"When we first heard about this patient and her link to China, we thought, 'Oh, okay, here it is,' " said Dr. Low, thinking back to Kwan Sui-chu, who was infected with the virus at a Hong Kong hotel in late February and who became Canada's first, or index, patient.
But the woman had quarantined herself for 10 days after returning from Asia and emerged disease-free before visiting her son. She "was a fly in the ointment," who turned the original index-case theory inside out, Dr. Low said.
She had not been infected abroad, but here, in a Toronto hospital: "She ended up getting SARS from her son."
That Thursday night, however, health officials knew no such details as they called a hasty news conference to reveal the new cases and to instruct people who had been at St. John's to put themselves into quarantine.
The next day, as Dr. Low and Toronto public health staff plowed through the troubling files at North York General, they counted more than 20 suspect cases and reached a chilling conclusion: The SARS outbreak had not ended.
And so they started from scratch once again, assembling a new command centre in a cramped room at North York General. That hospital looked like ground zero because the St. John's cases could be traced back to April 28, when a woman who turned out to have SARS was transferred to the rehabilitation centre from the orthopedic ward at North York General.
Reviewing the cases in North York General's orthopedic ward back through May and April, public-health workers discovered the earliest known suspicious patient to be a 96-year-old man.
The man had been admitted to North York General in early April after fracturing his pelvis. He did not undergo surgery as was thought, Dr. Low said, but was confined to his bed, first on a floor that would become the hospital's SARS area, then in the orthopedic ward.
On Easter weekend, April 19, the man developed pneumonia. "People - doctors and nurses - did ask at the time," Dr. Low said, 'Could this be SARS?' " But since they could find nothing to link the man to a known case, they chalked it up to a routine hospital-acquired pneumonia. More than half of such infections cannot be traced to a particular pathogen.
As Dr. Low reviewed the man's case, his mind darted back to a possible connection. On April 28, he, Dr. Henry and Mount Sinai microbiologist Tony Mazzulli had visited North York General to assess health workers who had contracted SARS after treating patients with the disease.
On that visit, hospital staff asked the three to review the cases of two psychiatric patients who had been granted Easter-weekend passes, and who returned with mysterious pneumonias on April 21.
"We were puzzled," Dr. Low said. "You don't see people like this getting pneumonia for no reason." But with no known connection to any SARS case, they chose to treat them as SARS patients without reporting them as such.
Yet Dr. Low believes there is a link between the psychiatric patients and the 96-year-old man, through a shared ventilation system, contaminated medical equipment or some other indirect contact.
But his instinct tells him that both cases likely have some connection to the hottest days of the original outbreak. During the week of March 24 - when suspect SARS patients began to turn up at all the city's hospitals - they were scrambling to set up SARS isolation wards.
Dr. Low wonders whether during that week an unrecognized SARS patient was inadvertently admitted to a regular ward, allowing the disease to smoulder just before tight restrictions were imposed.
The 96-year-old at North York General died on May 1. On May 2, his widow, who had visited her husband every day, developed symptoms of pneumonia and died, though she had been wearing a mask at the hospital. Before her death, she passed the disease to two of her children - who have recovered.
The spread of SARS in North York General is concentrated to half a dozen rooms of the orthopedic ward, including patients and health workers. As health workers and their families turned up at emergency wards last weekend, officials again traced contacts and charted new peaks in the outbreak.
Last Saturday, Toronto public health logged 36,000 calls on its SARS hotline in a single day - equalling the number of calls during the entire first leg of the outbreak.
By 2 a.m. Sunday, Dr. Low and his colleagues charted the new cases and they asked, " 'How did this bush fire start burning?' It spread because all of the precautions came down."
Dr. Basrur was boarding her plane to fly home from Montego Bay this week when she saw the headlines screaming that SARS had returned to Toronto.
"Oh no, not again," she thought, "How could this happen?"
Allison McGeer, head of infection control at Mount Sinai Hospital and a key member of the SARS containment team, said, "It is very easy to see with hindsight that we were tired; we wanted to believe it was over. And we thought that the surveillance systems we had in place would function. They didn't."
As well, some on the front lines were only too happy to be free of the tough restrictions SARS had heralded - particularly masks that made it tough to breathe. Others, however, were too frightened to take them off.
Barb Wahl, president of the Ontario Nurses Association, said some nursing homes told nurses to remove their masks because wearing them "frightens" the elderly patients.
The result was a patchwork system, and experts acknowledged that SARS cases could slip easily through the cracks.
"It's like 100 Smarties, and one of them is white chocolate on the inside, and you're supposed to be able to tell which one is white chocolate by looking on the outside," Dr. McGeer said.
The latest outbreak shows the need for "some system of audit within hospitals," Dr. Young said. "We do need some way of looking at every patient who develops a fever and respiratory symptoms.
"We stumbled, and we've got to figure what to do to try and not stumble again. Let's not kid ourselves that this is easy. So long as there's SARS in many parts of the world, the risk of it getting into a hospital anywhere remains. That's the reality."