Chinese health officials have confirmed earlier speculation that a father contracted bird flu from his son last December.
Researchers from Beijing's Chinese Center for Disease Control said a 24-year-old man spread the disease to his 52-year-old father in China's eastern province of Jiangsu. The son died, but the father survived.
In a report released Tuesday, the researchers said tests showed the two men were infected with almost genetically identical strains of the H5N1 virus. They also found that 91 people who had come into close contact with the men had not been infected with the virus.
Cases of human-to-human transmission of the virus are rare, but another case from December was confirmed in Pakistan last week. Most people who contract the virus have come into contact with infected birds.
On Monday, officials in South Korea and China confirmed fresh outbreaks of the H5N1 strain of bird flu.
South Korean officials said the latest cases of the H5N1 strain of bird flu were found in ducks at a farm in Jeongeup, a city about 250 kilometers south of the capital, Seoul. A separate outbreak was reported earlier at a chicken farm 30 kilometers away.
Also Monday, Chinese officials confirmed an outbreak of the H5N1 strain of bird flu on a farm in the remote region of Tibet has killed about 268 chickens.
Bird flu tends to be more active in lower temperatures and since the start of this year, China has confirmed three human deaths from the disease and several outbreaks among poultry.
The World Health Organization says 238 people around the world have died from bird flu since 2003. Indonesia reported two deaths last week, raising the country's confirmed death toll to 107.
Some information for this report was provided by AP and Reuters.