The Chinese Ministry of Health confirmed today that the country's first human case of H5N1 birdflu occurred two years earlier than previously thought, in November 2003.

A letter published by eight Chinese scientists on June 22 in the New England Journal of Medicine said that the bird flu virus had been isolated in a 24-year-old man who died in Beijing in 2003.

The man, surnamed Shi, became ill with pneumonia and respiratory disease in November 2003 and died four days after being hospitalized. China was then in the aftermath of severe acute respiratory syndrome (SARS), and the case was initially thought to be a SARS case. However, lab tests for SARS proved negative.

Parallel laboratory tests, carried out in collaboration with the World Health Organization (WHO), later confirmed that it was a human case of bird flu.

"This is the first human case confirmed on the Chinese mainland and the first human infection confirmed in the world in the current H5N1 virus cycle," said Roy Wadia, WHO Beijing office spokesman.

Before the case was revealed, China's first official human case of bird flu was thought to have occurred in Nov 2005. Nineteen human cases have been confirmed since then, including 12 deaths.

"Although this mainland case occurred two years earlier than other cases, there is no reason to think that China had an outbreak of bird flu in 2003," said Mao Qun'an, spokesman for the Ministry of Health.

"People shouldn't panic," he told Xinhua in an interview. "The country's bird flu surveillance capability is much stronger now than it was two years ago."

Mao said the Ministry was treating the case as a result of individual scientific research, and had no plans to probe more cases from that period.

But Wadia said it was "highly possible" that other cases of bird flu may have occurred during SARS and that they were misdiagnosed as pneumonia or treated as cases with unknown causes.

"There was no outbreak in poultry when this case appeared, which again highlights the importance of strengthening surveillance in the animal sector," Wadia said.

The first human cases of H5N1 bird flu occurred in Hong Kong in1997. Eighteen cases including six deaths were reported at that time. The current cycle of the virus began in late 2003 and felledits first victim in Vietnam in January 2004.

Globally, there have so far been 233 confirmed human cases of bird flu. By Aug. 7, 135 of the people had died, according to WHO figures.