China has confirmed that a father and son who were stricken with bird flu are the country's first confirmed infections within the same family.

But their cases showed no evidence that the virus has changed into a form that can easily be passed between humans, according to the World Health Organization.

The 24-year-old son from Nanjing, Jiangsu Province, died on December 2, becoming China's 17th fatality from the H5N1 bird flu virus. His 52-year-old father began showing symptoms a day later and was confirmed to have the disease. The father, identified only by his surname of Lu, was released on December 26 after 20 days in a hospital.

"The outbreak was a confirmed family cluster of human infection with H5N1 avian influenza between blood relatives for the first time on China's mainland," Hans Troedsson, WHO's representative in China, said yesterday.

An official at the Ministry of Health's press office confirmed the Nanjing cases were the first family infections but gave no other details.

More than 80 people who came in contact with the two men were monitored, but so far there have been no other reported infections.

Bird flu has killed at least 221 people worldwide, according to the WHO. Scientists have warned that if outbreaks among poultry are not controlled, the virus may mutate, potentially resulting in millions of deaths.

While the Ministry of Health "has not ruled out the possibility that the second case might have acquired infection from the first case, there was no evidence that there were any changes in the genetic sequences that make the virus more efficient in human-to-human transmission,'' Troedsson said.

Six days before the onset of his illness, the son visited a market where live poultry were slaughtered and sold, possibly exposing him to the virus, Troedsson said. While the father had direct contact with his son, the ministry could not rule out the possibility of his separate exposure to the market, he said.

The mainland has not confirmed any cases of human-to-human infection, although the sister of a boy who was diagnosed with H5N1 in 2005 later became sick and died. Authorities were not able to confirm whether the girl had been infected with H5N1.

Possible human-to-human transmission of the H5N1 virus has been reported in China's Hong Kong, Vietnam and Indonesia.

(Shanghai Daily January 26, 2008)