HONG KONG — China has reported a second fatality from the deadly H5N1 bird flu, a 31-year-old man who died of organ failure in the south-central Chinese city of Guiyang.

The flu, which is circulated in poultry and birds, has infected only 600 humans in the last decade, but has proven fatal in half the cases, so public health officials closely monitor its transmission. Scientists fear that the flu could mutate into a form that is highly contagious in humans.

In the most recent case, the man died Friday at a hospital in Guiyang. That city is also where a 21-year old woman died on Feb. 13. The official Xinhua news agency said that both victims had been in close contact with birds, the most common means of transmission.

The news agency added that 110 people who had been exposed to the victims had been released from quarantine.