Toronto's probable SARS cases have more than doubled as the city changed how it counts cases in line with World Health Organization (WHO) recommendations.
Doctors warned the number could go as high as 70 in coming days.
Provincial medical officials reported 29 probable cases of Severe Acute Respiratory Syndrome yesterday. The number, revised to conform with WHO guidelines, is up from 12 on Wednesday, when there also were 20 suspect cases. Doctors are monitoring 107 patients for infection, up from 50 people.
Under the WHO definition, Toronto will now include patients with pneumonia whose 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.
Dr Donald Low, chief of microbiology at Mount Sinai Hospital in Toronto, said the city could see probable case "numbers up in the 60s, 70s."
The flu-like illness, whose symptoms include high fever, dry cough and difficulty breathing, has killed 29 people in the Toronto area, the only place outside Asia to report deaths from SARS.
Dr Low said he thinks the current outbreak of the deadly disease seems to have peaked. However, more than 7,000 people are in quarantine and 13 patients are in critical condition.
Canadian and US authorities are investigating reports that visitors from Toronto may have spread the disease to the United States.