China confirmed on Tuesday that the country´s first human case of the H5N1 bird flu virus was in November 2003, two years earlier than originally reported, Xinhua news agency said.

The case had spurred questions about whether there might have been other human H5N1 infections in China prior to what had been its first reported human case, near the end of 2005.

Eight Chinese researchers published a letter in the New England Journal of Medicine in June saying a 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 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.

"The ministry confirmed the case by parallel laboratory tests, which were carried out in cooperation with the World Health Organization," Xinhua said in a brief report.

The scientists´ findings were 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 WHO.