The incidence of probable SARS cases in Toronto could rise more than fivefold to 60 or 70 as it reclassifies how it counts cases in line with World Health Organisation recommendations, one of the doctors leading the fight against the respiratory disease has said.
"We're talking numbers up in the 60s, 70s," Dr. Donald Low, chief of microbiology at Mount Sinai Hospital in Toronto, told journalists in an interview on today.
Low added he did not expect the WHO to renew an advisory that travellers avoid Toronto because the worst of the outbreak was over and there was no evidence of community transmission.
Toronto currently has 12 cases of Severe Acute Respiratory Syndrome it classifies as probable, some from an earlier outbreak between March and April and some part of a cluster that emerged last week. It is also examining more than 50 "suspect" cases.
Worldwide, there are about 8,300 SARS cases. The virus, which originated in southern China and has spread to 30 countries by travellers, has killed nearly 750 people.
The Toronto area has more than 5,100 people in quarantine, including about 2,000 staff and students at a high school north of the city that was closed yesterday after a student there showed SARS symptoms.
The flu-like illness, whose symptoms include high fever, dry cough and difficulty breathing, has killed 29 people in Toronto, the only place outside Asia where people have died from the disease.
Under a WHO definition, Toronto will now include patients with pneumonia where the cause cannot be adequately explained. The previous Health Canada recommendation on how to define probable SARS cases included only patients with a worsening respiratory illness.
"Health Canada's definition is fine when you are looking back at an outbreak, but when you are in the middle of an outbreak, the WHO definition is more practical," Low said.
He said the classification makes no difference in the long run as all suspect and probable SARS cases are treated the same way, and suspect cases may eventually develop progressive respiratory illness.
The number of cases of SARS is one element examined by both the WHO and the US Centres for Disease Control as they assess the advice they give about an area where SARS is prevalent.
A large and rising number of cases - 60 infectious cases plus five new cases a day - coupled with a spread of SARS outside a hospital setting and the risk it is being exported to other countries could trigger a WHO travel advisory.
"Hopefully, the WHO will not change our status. We have a problem that is identifiable. We can account for all the cases that we find, and I hope the WHO will look at that and give us credit for that," Low said.
The WHO put Toronto back on its list of SARS-affected areas earlier this week, after taking it off for 12 days, but stopped short of issuing an advisory.
A travel advisory could damage Toronto's already bruised economy as the summer tourist season begins. The area accounts for about a fifth of Canada's economic output.