China issued a bird flu alert on Wednesday and closed poultry markets around Beijing for disinfecting after a woman died of the virus.
It was the first such death reported in China in almost a year and the 21st there to date. However, the World Health Organisation said it appeared to be an isolated case.
The woman, 19, died of the H5N1 virus.
Tests on 15 people who worked in a poultry market in Yanjiao in Hebei province, where she bought the ducks, were negative.
The official Xinhua news agency said more than 100 people who had been in close contact with the patient, and one nurse who treated her, had come down with a fever but had now recovered.
The last human H5N1 death in China was in February last year when a woman, 44, died in southern Guangdong province.
According to WHO figures issued in mid-December, the H5N1 virus has infected 391 people, killing 247 of them, since it resurfaced in Asia in 2003.