The reports of a possible new outbreak in Toronto came on a day of rare good news out of Asia, where severe acute respiratory syndrome originated.
For the first time since late March, no new cases were reported in Hong Kong on Saturday. Taiwan had no new deaths for a second day in a row and Chinese officials said they saw a "notable downward trend."
Singapore was culling stray cats as part of nationwide cleanup campaign sparked by the SARS crisis, a spokesman said Saturday, a day after researchers in Hong Kong said they found the virus in civet cats - a delicacy eaten by some Chinese, and two other small animals.
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.
An editorial cartoon in Saturday's National Post newspaper showed a family of four walking hand-in-hand 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 nearly 700, the vast majority of them in Asia. Canada saw the largest outbreak outside of Asia, with about 150 cases and 24 deaths.
World Health Organization spokesman Dick Thompson said one new case in Toronto tested positive for SARS, and 31 other people with respiratory illness were being tested.
But Thompson said the U.N. body would have to study the situation more closely before deciding whether to place Toronto back on a list of SARS-affected areas or begin considering a travel warning for the city.
Officials of the WHO and Health Canada held a hastily called teleconference Saturday after the Geneva-based organization demanded additional information about the large new cluster of possible SARS cases in Toronto.
Following the brief conference call, Thompson said the organization still wants more information about the possible new outbreak, but for the time being will not change Toronto's status as a city in which local transmission of the disease is deemed not to be occurring.
The two agencies are scheduled to talk again Sunday, he said. "It's a situation we're going to pay a lot of attention to."
Ontario and Toronto health officials said Friday an apparently undiagnosed SARS case at North York General Hospital may have infected health care workers, other patients and their family members on 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.
Hanif Kassam, medical officer of health in York Region north of the city, said Saturday that at least 40 people who had direct contact with the possible new SARS cases have been traced so far.
"The number (of exposed people) is likely to increase over the next 24-48 hours," said Kassam, adding the source of the possible outbreak remained unclear.
Reporter Chris Mavridis of CFRB Radio in Toronoto says city health officials have quarantined 500 people they believe may have come in contact with the virus, and 70 healthcare workers in one hospital have been put in isolation. Units at four hospitals have closed. That includes two emergency rooms.
The possible new cases in Toronto prompted the U.S. Centers for Disease Control and Prevention to issue a new travel alert Friday for Toronto, Canada's largest city. That's a step short of warning against unnecessary travel there.
Toronto health officials ordered restricted access and use of protective masks and gowns for all area hospital emergency rooms, repeating steps taken against SARS earlier this year.
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 after strong lobbying by Canadian officials, who called it unwarranted. 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.
Dr. Donald Low, a microbiologist and major figure in Toronto's anti-SARS efforts, said the new cluster could have included two elderly patients who died in recent weeks. If confirmed, they would increase the SARS deaths in the Toronto area to 26.
Dr. Colin D'Cunha, the province's commissioner of public health, said it was uncertain whether all the possible cases would be confirmed as SARS.
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, including cheap packages for lodging, meals and entertainment, including Toronto Blue Jays baseball games.
Hong Kong rejoiced after the World Health Organization on Friday lifted a SARS advisory against nonessential travel to the territory, which has hit its economy hard. But some cautioned a full recovery could take time with wary tourists slow to return.
"Hong Kong smiles again," the Chinese-language Apple Daily declared on page one. "What a difference a day makes," said the English-language South China Morning Post.
No new SARS cases were reported in Hong Kong for 24 hours for the first time since authorities began releasing figures in March, health officials said Saturday. But two more people died from the disease.
Hong Kong has reported 262 deaths from SARS and 1,724 cases.
In Hong Kong, Health Director Dr. Margaret Chan warned at a news conference that people should not become complacent, because SARS is not yet wiped out in the territory.
"It can go both ways anytime," Chan said.
Chan said Hong Kong has decided to maintain temperature checks of people at border crossings for one year, in hopes SARS will not be spread by travelers.
Hong Kong's neighbor, southern mainland Guangdong province, where SARS is believed to have originated, was also taken off the WHO travel advisory list Friday. WHO still advises against all nonessential travel to Beijing, and four other Chinese regions, as well as to Taiwan, because of continuing new transmission of SARS.
In Beijing, the hardest-hit region in the world, a city spokesman said new cases in the city were on a "notable downward trend," although the Health Ministry later announced a slight uptick in numbers of infections on Saturday.
Taiwan on Saturday said it had no new SARS deaths for the second day in a row and the rate of infection plummeted from highs earlier in the week.
"The situation has stabilized, so people can begin resuming normal lives," said Lee Ming-liang, head of the Taiwan SARS Control Committee.
Taiwan's death toll remained at 60, while the number of infections rose by 10 to reach 548. Daily increases in infections reached as high as 65 on Thursday.
Despite decades of enmity, China offered to send Taiwan medical experts with experience fighting SARS, along with 100,000 surgical masks, 200,000 protective suits and five ambulances customized to prevent air that might be infected with the virus from escaping.
The two sides split amid civil war in 1949, and China still claims Taiwan as its own territory.
Researchers in Hong Kong announced Friday they had have found evidence of the SARS virus in three types of small mammals including the civet cat, which is eaten as a delicacy by some Chinese. But the WHO said it cannot rule out the possibility the animals acquired the virus from humans.