Chinese son likely gave bird flu to father - report

They also tested 91 people the two men had come into close contact with. None of these people became infected.

The young man had a high fever, cough and watery diarrhea and his father nursed him intensively in the hospital.

The younger man died but his father got the flu drugs Tamiflu and rimantadine as well as serum from a woman inoculated with an experimental H5N1 vaccine and recovered.

"With the exception of occasional infection in health workers, all published incidents of possible or probable person-to-person transmission report transmission between genetically related individuals," Nguyen Tran Hien of Vietnam's National Institute of Hygiene and Epidemiology in Hanoi, and colleagues wrote in a commentary.

"Although this finding could be related to the intensity and intimacy of contact between family members, host genetic factors might also play a part in susceptibility to H5N1," they added. So anyone in close, prolonged contact with an H5N1 victim should get flu drugs just in case, they said.

Last week the World Health Organization said some human-to-human spread likely occurred when three brothers in Pakistan became infected with H5N1 last year.

The largest known cluster of human bird flu cases occurred in May 2006 in Indonesia when at least 7 family members died.