But the U.N. agency cautioned in a report that new outbreaks could still occur.
“The experience in Toronto, where more than 70 new cases have been reported since 26 May, underscores the risk of a resurgence of cases and the constant need for vigilance,” the report said.
The WHO also reported that June 4 was the first time since March 28 that no deaths were reported from the disease anywhere in the world.
China, the hardest-hit nation, had its first day of no new reported cases or deaths since April. WHO officials said evidence over the last two weeks indicates the Chinese are succeeding in bringing their epidemic under control, but that the disease is by no means contained there.
“We are beginning to see the benefits of the scaling up of the Chinese response — the active surveillance, the home quarantine of contacts … the improvements in the hospital infection control, the tightening up of the whole surveillance system,” said Mike Ryan, who heads the global SARS response network for the WHO.
Since the flu-like illness emerged in the southern province of Guangdong in November, SARS has killed at least 334 people on the mainland and infected more than 5,000.
But since the beginning of May, the numbers have been steadily decreasing from the epidemic’s peak of more than 150 cases a day. In the past week, the number of cases per day has remained in the single digits, according to the WHO.
Ryan’s optimism was tempered by a hesitance to draw any firm conclusions from the fact that China detected no new cases or deaths Wednesday.
“We can’t say anything based on one day,” he said. “We are going back now and talking to the Chinese to try to make sure that their surveillance is very sensitive and they are not missing things…”
On Tuesday the WHO cast doubt on China’s tally of SARS cases.
“It may simply be that there has been a dramatic drop off in the number of SARS cases, but clearly because of the way that SARS emerged in China, China has a credibility problem,” WHO spokesman Ian Simpson said.
China would be considered to have controlled its outbreak when the country had gone for 20 days without a new case, Ryan said.
“The trend is very encouraging across the whole of China,” Ryan said, “but all we need is one infectious case to get into one poorly equipped hospital and we’re back in the middle of it.”
Vietnam has remained SARS-free since April 8. In Singapore, the last probable case acquired in the country was isolated May 11. No new cases have since been detected in either place despite a high level of alert and aggressive investigation of all rumored cases, according to the WHO.
The agency said that success underscores the WHO position that SARS can be contained despite the lack of a vaccine, reliable diagnostic tests and specific treatment.
Despite the promising prognosis worldwide, the recent discovery that the virus exists in animals appears to be a complication.
Researchers have found the virus in civet cats at a live food market in China, but it is unclear whether the civets are the source of the human outbreak. If they are, or if another animal is, there is a chance the virus could jump to humans again — just as bird flu did in a few cases this winter in Hong Kong.
“If we were purely dealing with a human disease, with no animal reservoir, then I would really be very confident now that we could eliminate this completely,” Ryan said.