The 27-year-old man was a researcher in a laboratory that is investigating severe acute respiratory syndrome, and Singapore said it believes he caught the virus at work. The World Health Organization said it would not issue any new travel advisories.
"There is no need for panic," Shigeru Omi, the WHO's director for the Western Pacific region, told reporters, adding that there is confidence in the strength of Singapore's SARS surveillance system.
The Health Ministry in Singapore confirmed late Tuesday that the man had SARS. Ministry spokeswoman Bey Mui Leng said the man had tested positive to two SARS examinations in Singapore on Monday and Tuesday.
Samples of the man's blood were sent to the United States for further testing. Singapore would continue to treat the man as a SARS carrier even if the U.S. results contradict the positive results obtained locally, Bey said.
"The single case is an isolated case," Balaji Sadasivan, Singapore's minister of state for health, said on the sidelines of a regional WHO conference in Manila. "There is no person-to-person transmission, so there is no outbreak."
The last case of SARS reported in the world was June 15 in Taiwan.
SARS first emerged in China in November. Over the next eight months, it killed more than 900 people worldwide and infected more than 8,400.
In China on Wednesday, health authorities said Guangdong province, where the illness emerged in November, has agreed to quickly notify neighboring Hong Kong about disease outbreaks in the future.
When the first SARS cases appeared, Guangdong health authorities did not report the outbreak to Hong Kong, and China's central government did not disclose information about the disease until February. By that time, Hong Kong was enveloped in a full-scale epidemic that ultimately killed 299 people in the territory and sickened hundreds more.
Sadasivan said the man with the apparent new case "most likely" was infected in a laboratory he visited Aug. 23. The lab and another facility where the man was doing research on the West Nile Fever virus have been closed as a precaution.
"We will audit them and run through all the safety procedures in the laboratory," he said.
He also said 25 people who had been in contact with the man were quarantined for 10 days and none appears to have the disease.
Omi said the Singapore case does not show typical signs of SARS but that the man, who is already well, may have not been exposed heavily or may have had a strong immune response that suppressed usual symptoms like pneumonia.
He said the man was at the laboratory six days after a visit by people who were dealing with the SARS virus. The man developed a fever three days later.
Asked if the WHO was ready to deal with another SARS outbreak, Omi said it depends on whether the virus remains the same or has mutated.
"I think we can deal (with it) better than before because we have learned a lot already," he said. "But ... if the virus undergoes genetic transformation, the story would be very different."
Bey said the man — the 239th person to have the illness here — was recovering and in isolation at the Communicable Diseases Center at the Tan Tock Seng hospital — the island nation's dedicated SARS facility.
Singapore recorded 33 deaths from the virus, which sent its economy into a tailspin by hitting its vital tourism and services industries.
Singapore Airlines said Wednesday it was awaiting word from officials on whether it should reintroduce its tough SARS measures on all flights. In a statement to The Associated Press, the national carrier said it was ready to provide masks and disinfect all aircraft if requested.