The ministry said experts made the decision based on the patient's symptoms, epidemiological investigation results and laboratory tests.

All the people who had close contact with her had been tracked down and put under medical observation, with no one feeling unwell, it said.

According to Beijing Municipal Health Bureau, Liu had only contacted with two persons, one is her mother and the other is the taxi driver who carried her to Peking University First Hospital.

Neither of the two had shown flu symptons, said Deng Ying, director of Beijing CDC.

Expressing his appreciation of the 18-year-old Liu for keeping a clear diary about her journey in Beijing, Fang Laiying, director of Beijing Municipal Health Bureau, said, "she even kept the receipt from the taxi driver, otherwise it would be difficult for us to find out the driver,"

"The quarantine hospital had arranged three doctors and three nurses for Liu and took strict medical observation on her," said Mao Yu, president of Beijing Ditan Hospital.

"Liu is in stable condition as her temperature is getting normal and her appetite getting better," Mao said.

The health ministry has reported the case to the World Health Organization, Hong Kong, Macao and Taiwan and relevant countries.

The first two cases in mainland China are Chinese nationals, Bao and Lu, who had been students in the United States and Canada, and were traveling back to their homes in the past days of the month, contracted the flu strain and developed symptoms shortly after they set foot in China.

(Xinhua News Agency May 17, 2009)