Tow cases of bird flu in humans involving family members in Nanjing, Jiangsu Province, have been effectively contained, China's Ministry of Health announced.

It added all close contacts involved had been released from medical observation.

"None of those in close contact showed unusual symptoms and they were all released from medical observation on December 12," the ministry said.

China announced on December 2 that a 24-year-old man surnamed Lu in the provincial capital Nanjing died of H5N1 infection. On December 7, the man's father was also confirmed to be infected with the virus.

Eighty-two people who had contact with either man were put under close medical observation.

"The father, who has been under intensive medical treatment, is in a stable condition and showing signs of improvement," the ministry said in the statement.

Neither of the men was said to have had contact with sick or dead poultry so the source of the infection remained unknown.

Health Ministry spokesman Mao Qun'an said earlier there were several possibilities for infection in the second case, including close contact between the father and the son.

Joanna Brent, a Beijing-based WHO spokeswoman, told Xinhua that "there is no strong indication of human-to-human transmission. But because this possibility cannot be ruled out, the WHO is monitoring this case closely."

"If this (the second case) was proved to be a case of human-to-human transmission, it seems likely that the transmission is inefficient since, so far, there is just one confirmed case out of 83 close contacts and the two cases were directly related, with no second-generation transmission," she said.

She also said that at this stage a possible common source has not been identified and based on preliminary laboratory results of these two cases, the possibility of infection from two separate sources is least likely.

Brent said that like most H5N1 cases in China, these cases were not foreshadowed by a poultry outbreak reported to the Ministry of Agriculture.

"This suggests that strategies for monitoring H5N1 in poultry need further strengthening," she said.

(Shanghai Daily December 15,2 007)