The 19-year-old woman died of the H5N1 virus after coming into contact with poultry in Hebei province, bringing the total death toll in China to date to 21.

In Hebei's Yanjiao, where the dead woman had bought ducks, poultry markets were closed and the sale of live birds stopped as workers in masks and white coats sprayed disinfectant.

The World Health Organisation said it appeared to be an isolated case.

'We are concerned by any case of human H5N1 infection, however, this single case, which appears to have occurred during the slaughtering and preparation of poultry, does not change our risk assessment,' the WHO said in a statement.

'WHO expects the ministry will continue to keep it updated on this case, and is prepared to offer technical assistance if requested,' it added, referring to the Health Ministry.

The virus is generally more active during the cooler months between October and March, although the new Chinese case points to holes in surveillance of the virus in poultry.

No poultry, no outbreak
Paul Chan, microbiologist at the Chinese University in Hong Kong, said it was worrying that this case was not accompanied by the detection of the virus in poultry nearby.

'The source of this infection seems to be poultry or the market (where the girl bought the ducks). If that is true, we need to know why we missed the outbreak of the virus in poultry or in the market,' he said.

'If there was an outbreak in the market, there should have been large numbers of poultry deaths. If people in the markets and the government can't recognise this, then we have a serious problem on our hands,' Mr Chan added.

The H5N1 strain remains largely a disease among birds but experts fear it could change into a form that is easily transmitted from person to person and spark a pandemic that could kill millions of people worldwide.

The last human H5N1 death in China was in February last year when a 44-year-old woman died in the southern province of Guangdong.

With the world's biggest poultry population and hundreds of millions of farmers raising birds in their backyards, China is seen as crucial in the global fight against bird flu.

Since the H5N1 virus resurfaced in Asia in 2003, it has infected 391 people, killing 247 of them, according to WHO figures released in mid-December.

Vietnam's agriculture ministry has confirmed an outbreak of bird flu among poultry in the northern province of Thanh Hoa, where a girl was hospitalised with the deadly disease last week.

Thanh Hoa is the second province in two weeks to report an outbreak of the bird-borne illness among poultry, the other being Thai Nguyen, directly north of the capital.

The health ministry has said an 8-year-old girl from Thanh Hoa was infected with bird flu after eating poultry. -- REUTERS

Read also:
China steps up poultry checks