TAIPEI, Taiwan — Taiwan reported its first SARS case in five months on Wednesday — a scientist who allegedly ignored World Health Organization safety rules and worked with spilled virus samples without wearing a protective gown and gloves, officials said.

The news caused Taiwan's jittery stock market to tumble, and the island's top health officials scrambled to ease fears that the highly contagious virus would spread.

"It looks very much like an isolated event," World Health Organization spokeswoman Maria Cheng said. "He was traveling to Singapore but he was asymptomatic while there and, according to data we have, patients are not contagious while asymptomatic."

The 44-year-old man, who wasn't identified, was a senior scientist studying SARS in Taipei at the state-sponsored Institute of Preventive Medicine, officials said. He tested positive for SARS on Wednesday after undergoing WHO-approved tests.

"Right now, he's the only one who's been infected," Health Minister Chen Chien-jen said.

The researcher, who lives in suburban Taipei, developed SARS symptoms on Dec. 10, the same day he returned home from a conference in Singapore. But officials believed he was exposed to the virus in his lab, as early as Dec. 5.

Dr. Shigeru Omi, the WHO's Western Pacific regional director, told reporters in Manila, the Philippines, that the Taiwanese scientist was working without protective gear, such as gloves and a gown.

"What we hope is that all the researchers involved in this kind of work will comply with this recommendation guideline we have already given to them," Omi said.

Omi said that on Dec. 5 the scientist observed some spilled liquid on the surface of a test tube. "So this is most likely how the contaminated liquid infected this scientist," Omi said.

The scientist showed no signs of a fever — a key SARS symptom — when his temperature was checked at Taipei's airport upon returning from Singapore on the afternoon of Dec. 10, the center said. But he became sick in the evening, CDC said.

Chen doubted that the scientist had been a public threat. The official said SARS isn't believed to be contagious until the onset of a fever. The virus has a maximum incubation period of 10 days, according to the WHO.

Chen said that since the scientist was not in the official contagious period during his travels, passengers on his China Airlines flight would not be individually informed about the case. But he urged the passengers to be vigilant for SARS symptoms.

The scientist also quarantined himself at home as soon as he developed SARS symptoms, officials said.

Singapore reported no suspected SARS cases Wednesday, but officials quarantined 70 people who had contact with the Taiwanese patient.

This was the second time in about four months that a researcher in Asia has caught SARS. Singapore reported a similar case in September, and investigators later blamed the infection on "inappropriate safety procedures" in the lab.

Henk Bekedam, WHO representative in China, told reporters in Beijing that Taiwan's new infection is "a clear reminder again that we have to be extremely cautious working with the SARS corona virus."

Taiwan's case brought back memories of the outbreak that began last April and lasted until July when WHO removed the island from a list of SARS-infected areas. Taiwan ranked No. 3 in the world behind China and Hong Kong for SARS deaths and cases.

Many Taiwanese were relieved to hear officials say the SARS case involved a laboratory — not a public place where thousands of people might have been exposed.

But Taipei insurance saleswoman Virginia Su was still worried that SARS would hurt Taiwan's business climate.

"This is terrible. It's very bad news," the 41-year-old woman said.