Just weeks after Canada declared itself free of SARS (search), officials announced 33 suspected cases of the virus in Toronto Saturday, while hospital workers were scrambling once again to contain a possible outbreak.

At least 500 people possibly exposed to the virus were told to quarantine themselves at home for 10 days, said health officials in Toronto (search).

Dr. Colin D'Cunha, the Ontario commissioner of public health, said 33 people with respiratory illness were being tested for SARS. All were believed to have contracted the illness in hospitals over the past month, he said.

Two of the suspected cases involved elderly patients who died in recent weeks. If confirmed, they would raise the SARS death toll in the Toronto area to 26.

Access to all Toronto-area hospital emergency rooms was restricted, and emergency room workers were ordered to wear protective masks and gowns, repeating steps taken earlier this year in Canada's largest city. Toronto has suffered the largest SARS outbreak outside of Asia.

A formal definition of a probable SARS case requires a link to a known SARS case, and that has yet to be established, D'Cunha said. But the officials were proceeding as if all the possible new cases were SARS.

"Clinically, we think they have it," said Dr. Donald Low, a microbiologist at the forefront of Toronto's anti-SARS efforts.

The new cluster of possible cases of severe acute respiratory syndrome prompted U.S. health officials to issue a new travel alert for Canada's largest city.

The World Health Organization (search), however, did not issue a travel warning, saying more confirmation of an outbreak was needed before advising against travel to Toronto. The WHO did confirm one new positive case.

In Asia, the Taiwan government announced another 12 Taiwanese SARS deaths Sunday, the first time in three days that new SARS deaths were reported in Taiwan. But Taiwan also said the number of new infections continued to fall to only three.

The SARS death toll in Taiwan now stands at 72, the Center for Disease Control said.

In Hong Kong, however, for the first time since late March, no new cases were reported on Saturday. Taiwan has the world's third-highest SARS toll after China and Hong Kong.

Despite the inability to trace the new suspected cases to known cases, officials in Toronto said there was no danger of an uncontrolled outbreak.

"This is not a disease out there in the general community," D'Cunha said.

A WHO spokesman in Geneva said one new case in Toronto tested positive, and results on other cases were expected shortly. Dick Thompson said Canadian officials reported 31 cases of respiratory illness they were checking for possible SARS. The figure he was given excluded the two dead patients.

Canada received the latest bad news in a dismal week after the discovery of mad cow disease in the cattle heartland of Alberta prompted the United States and other countries to ban imports of Canadian beef products. Health officials also recently warned that Canada can expect an increase of West Nile virus in the summer mosquito season.

On Saturday, investigators placed three more Alberta farms under quarantine in search of North America's first case of mad cow disease in a decade.

Alberta Agriculture Minister Shirley McClellan said 16 farms were now under quarantine — 11 in Alberta, where the recent case of bovine spongiform encephalopathy, or BSE, was found; two in Saskatchewan to the east; and three in British Columbia to the west.

An editorial cartoon in Saturday's National Post newspaper showed a family walking outdoors exclaiming, "Aaah ... the weekend," all dressed in protective suits and helmets — even the dog.

SARS has spread to more than 8,000 people around the globe and killed 708, the vast majority of them in Asia. Canada earlier saw about 150 cases and 24 deaths.

Ontario and Toronto health officials said Friday an apparently undiagnosed SARS case at North York General Hospital (search) may have infected health care workers, other patients and their family members in one ward in late April.

A patient transferred from the ward to St. John's Rehabilitation Hospital was considered the likely source of four more cases under investigation, they said. It was not known where the new cases may have come from.

A third hospital, St. Michael's, closed its neurosurgery units until June 2 after learning a potential new SARS patient was treated there recently without respiratory precautions, D'Cunha confirmed Saturday. More than 50 staff members were put into 10-day quarantine.

Toronto was removed from the WHO list of locations with SARS earlier this month when more than 20 days — the length of two SARS incubation periods — had passed since the last known case on April 19.

WHO also had issued a travel advisory for Toronto on April 23, but lifted it a week later. Canada agreed to WHO demands to increase airport screening of international travelers and said it started using fever-detecting scanners at airports in Toronto and Vancouver, British Columbia.

The SARS outbreak that first appeared in March hit Toronto's vital tourism and convention industry hard as travelers canceled plans to visit the city. Ontario and city officials launched aggressive marketing campaigns to lure back business and visitors.

The Associated Press contributed to this report.