BEIJING - The father of a Chinese man who died of bird flu has been infected with the virus that causes the disease, the World Health Organization confirmed Friday, saying it could not rule out the possibility of human-to-human infection.

Joanna Brent, a Beijing-based WHO spokeswoman, said the father began showing symptoms Monday and was confirmed as having the H5N1 virus on Wednesday. She said he has been hospitalized.

Brent said there was no evidence the man had been infected by his 24-year-old son, who died on Dec. 2, but could not eliminate that possibility.

"Because the possibility of human-to-human transmission cannot be ruled out, we will be monitoring this case closely," Brent told The Associated Press. "If it is found to be easily passed between humans, we would be concerned."

She said it was also possible that the two men were infected by the same source, or that they were infected separately from different sources.

Chinese news reports gave the man"e;s age as 52. Both he and his son, who lived in the eastern province of Jiangsu, were identified only by their surname, Lu.

Jiangsu"e;s Provincial Disease Control and Prevention Center said the son — China"e;s 17th official fatality from bird flu — had not had any known contact with dead poultry, and there were no reported outbreaks of the disease in the province.

Brent said health authorities were monitoring 68 people who had been in close contact with the son, and none have shown symptoms of H5N1 infection.

Sporadic human-to-human transmission of the H5N1 flu strain has been reported in Hong Kong, Vietnam and Indonesia, but none of the cases have been proven.

Dr. David Nabarro, the U.N. official coordinating the global fight against bird flu, has said the risk of a worldwide pandemic remains as great today as it was when H5N1 first gained attention in 2005.