TORONTO (AP) – A suburban Toronto high school was closed and its 1,700 students and staff placed under quarantine after a classmate showed symptoms of SARS, health officials said Wednesday.

The move means more than 5,000 people in the Toronto area have been told to stay home for 10 days as authorities sought to control the spread of a new cluster of SARS cases.

The new cases of severe acute respiratory syndrome included two deaths. A third death last weekend, that of a patient who had been sick for months, raised the overall toll in the Toronto area to 27 dead among about 150 cases.

The new cases put Canada’s largest city back on a World Health Organization list of SARS-affected areas. Three more probable cases from the initial Toronto outbreak in March and April also remained hospitalized.

On Wednesday, the WHO told Canada to broaden its definition of SARS cases following concerns that a new definition adopted Monday has led to an incomplete accounting of the situation.

Dr. Donald Low, a microbiologist and key member of the anti-SARS team dealing with the Toronto outbreak, said the number of new probable cases would be well over 20 – rather than the current nine – if officials used the same definition as applied in the initial outbreak in March and April.

Under the new guidelines, only patients showing a severe progressive respiratory ailment are considered probable cases. Previously, a respiratory ailment visible on X-ray was a criterion, but the new definition is more restrictive.

Dr. Denise Werker of the WHO’s communicable diseases section said discussions with Canadian health authorities Wednesday focused on the issue.

Still troubled by the biggest SARS outbreak outside of Asia, Toronto now faces further harm to its crucial convention and tourism industry because of the new cases.

Prime Minister Jean Chretien insisted Wednesday that the city was safe to visit.

“We had a new case that appeared last week and it was confined in the hospital section of the city of Toronto … it is under control,” Chretien told a news conference in Athens, Greece, where he was attending a meeting of European Union leaders. “This is a problem that is serious, but it is not dangerous at all to travel to Toronto.”

The possible SARS case at Father Michael McGivney Catholic Academy in Markham, a northern suburb of Toronto, involved a the son of a health care worker linked to a Toronto-area hospital with known SARS cases.

The student was listed as a suspected SARS case Wednesday, but Dr. Murray McQuigge, a York Region Public Health official, said there was no doubt he had the virus.

“We’re saying this person does have SARS. This is deadly serious business,” McQuigge told a news conference. He read out guidelines for home quarantine, including no visitors, sleeping in a separate room from anyone else and wearing a respirator mask when in contact with others. He said health authorities will deliver the masks to those in quarantine.

Health officials said the school was closed until June 3 as a precaution, but acknowledged they still were learning about the illness that has erupted anew after the initial outbreak appeared.

under control.

“None of us has dealt with a disease that is this infectious in a hospital setting before, other than tuberculosis” and a few others, said Low.

The WHO designation of Toronto as SARS-affected is routine for places with new cases of the illness. However, WHO spokesman Dr. David Heymann said Wednesday there were no plans to re-impose a warning against travel to the city.

In response to the new cases, health authorities re-imposed strict controls on Toronto-area hospitals – closing those where the new cases were found to new patients and limiting access to emergency rooms in all others.

On May 14, Toronto was removed from the WHO list of SARS-affected areas after more than 20 days passed without a new case being reported.

AP-ES-05-28-03 1621EDT

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