National lab finds an extra 120 people may have had SARS; experts concerned

Canadian Press ^ | 06-19-03

[Brian S]

TORONTO (CP) - As many as 120 people who aren't on the list of Canada's probable or suspect SARS cases may actually have had the disease, testing done by Health Canada's National Microbiology Laboratory has shown.

And experts say it's crucial to find those individuals and figure out whether they actually had SARS and whether they have spread it to others. "It's a worry. It's an important thing to try to figure out why, (and) what this means," said scientific director Dr. Frank Plummer.

The Winnipeg lab, in conjunction with Ontario officials and public health authorities in the locations where the individuals live, is beginning a study to track down the people, their doctors and their contacts to ensure that other SARS cases aren't simmering, undetected, in Toronto and other southern Ontario communities.

"Look what happened at North York," said leading SARS expert Dr. Donald Low, referring to North York General Hospital, the epicentre of Toronto's second SARS outbreak.

"There was a cluster in a family that wasn't recognized. Maybe there's a cluster in Belleville that we just haven't recognized."

Even if further study shows that no new clusters are simmering, the findings suggest Ontario must have dodged a few SARS bullets, the experts admit.

"Oh, I think there might have been quite a few more from just glancing through the data that we have," said Plummer.

"There probably were several other importations and we've probably been lucky, but that's just really supposition at this point by me. Once this investigation's completed, we'll know a lot better."

Canada has officially recorded 245 probable and 193 suspect cases of severe acute respiratory syndrome since the disease hit these shores in late February, the vast majority in the Toronto area.

One of the puzzling positive test results that Plummer's lab has turned up was for a woman from Belleville, which is why Low referred to that city, about two-hours drive east of Toronto. Another was for a man from the Grey Bruce area, north of Toronto, who had been listed as a suspect SARS case in March.

The man, who had been believed to have contracted SARS in Singapore, was eventually struck from the list when it was found he had influenza B, which could have caused his symptoms.

But Plummer's lab recently informed his local medical officer of health that the man probably had SARS as well.

That case and another like it at North York General suggest it may be time to again rewrite the definitions of probable and suspect SARS, Low said.

A psychiatric patient at North York who appeared to have SARS in April but who was not known to have been in contact with a SARS case was eventually ruled out when lab tests showed he had mycoplasma, a pathogen that causes pneumonia.

Weeks later blood tests revealed the man also had SARS.

The current definitions allow authorities to rule out a case if another reasonable diagnosis is discovered. The North York and Grey Bruce cases suggest that's no longer an option, Low said, noting that 10 to 15 per cent of community acquired pneumonias are caused by more than one agent.

"It's naive to think to think that people only have infection with one organism. It's naive to think that because somebody has influenza B that they couldn't have SARS," he said.

"That's dangerous."

Since the SARS outbreak began, the Winnipeg lab has been working overtime, processing samples submitted from about 2,100 people so far.

Plummer doesn't have enough information on each individual case to determine whether these 120 people are false positives, people who were infected but whose symptoms were so mild they didn't meet case definitions or actual SARS cases who somehow slipped through public health's nets.

He doesn't even know if they all would have been quarantined, though some, like the Grey Bruce man, definitely were.

Dr. Andrew Simor, chief microbiologist at Toronto's Sunnybrook and Women's College Health Sciences Centre, said testing done by their lab corroborates the Winnipeg lab's findings.

"We've also found a handful of these people at our hospital. And it's hard to know how to interpret them," he admitted.

"Of course of most importance is are these people who are potentially infectious? And to this point in time, I'm not aware that any of these people . . . have actually been responsible for transmission of disease. And ultimately that's what's most important."

But public health officials cannot afford to assume that just because they haven't identified that kind of below-the-radar transmission doesn't mean it hasn't happened.

"Well, that's one reason for doing the study, is to make sure we haven't missed it," Low said.

"You'll only know this for sure if you go out, you do the interviews, you draw the blood to see if they really had disease and you ask the question . . . 'Has there been anybody else with illness that has been associated with them?' "

That study will also tell the world's SARS experts a lot more about how reliable a positive test for SARS is, Simor added.

"In most cases, a positive test means that they've got the disease, but that isn't 100 per cent," he said.

"And if we're going to understand this any better, we need to track these 120 or so individuals down and do the interview and get the serology (blood work) to try to better understand the significance of the positive test results."