China has invited UN experts to observe its tests to verify findings by eight Chinese scientists that a man who died in late 2003 contracted the H5N1 bird flu virus, the World Health Organization said on Wednesday.

The man’s case has spurred questions about whether there might have been other human H5N1 infections in China prior to its first reported human case near the end of 2005.

“We’ve got two experts who are currently in Beijing. They are observing and discussing the testing of the samples from the November 2003 case,” said WHO spokesman Roy Wadia.

“I don’t know how long the mission will last, but I don’t anticipate it stretching beyond a few days from now.”

The Chinese researchers published a letter in the New England Journal of Medicine in June. They said the 24-year-old man, who was admitted to hospital in November 2003 for respiratory distress and pneumonia and later died, had been infected with H5N1.

The report was one of the clearest indications yet that the virus might have been brewing for much longer in the vast country than what had been reported.

The H5N1 virus made its first known jump to humans in Hong Kong in late 1997, and then more or less petered out until it re-emerged in parts of Southeast Asia in late 2003, when it killed three people in Vietnam.

The virus is known to have infected 19 people in China since last year, killing 12 of them, according to the WHO.

In Thailand, an official said on Wednesday that a 17-year-old male had died of H5N1, the country’s 15th death from the disease. The youth died on Monday in the northern province of Pichit, where authorities have confirmed the country’s first outbreak of the virus among poultry in eight months.

Still largely a scourge in birds, it has killed 133 people around the world since late 2003. But experts fear the virus could trigger a pandemic if becomes easily transmissible among people.

The 24-year-old Chinese man exhibited clinical symptoms of the respiratory disease SARS when he was admitted to hospital but tested negative for that.

His virus samples genetically resembled H5N1 viruses taken from Chinese chickens in various provinces in 2004, the eight experts said.