The latest human case of bird flu infection in China is in an area where no animal outbreak has been reported and officials are trying to trace how the 10-year-old girl contracted the virus.

The fourth human infection of the deadly H5N1 strain of the virus in the country was in the Guangxi Zhuang Autonomous Region, Xinhua reported late on Tuesday, quoting the Ministry of Health.

The girl was hospitalized on November 23 and local doctors said yesterday that her condition was stable.

The girl in the South China region reportedly had contact with domestic poultry one to two weeks before she fell ill, the World Health Organization (WHO) said yesterday.

But details were sketchy; the WHO does not know where the poultry was, or whether any fowl were ill, or how she contracted the virus, spokesman Roy Wadia told China Daily.

Local experts, as well as those sent by the Ministry of Health, are investigating potential sources of exposure.

Wadia described a few scenarios on how the girl could have been infected:

If only a few domestic birds die in a backyard, it might be difficult to identify the deaths as part of an outbreak but people who come into contact with such birds may get infected.

If poultry are not vaccinated properly they may be harbouring the virus, without getting sick or dying, and spreading infection, possibly to people who come into contact with them.

"Although this is only a guess, there have been some examples in which human cases of bird flu were reported first and then the animal epidemic," Roy said.

The two people in Anhui Province who died after contracting the H5N1 virus were in areas that did not have any reported outbreak in poultry yet both of them had contact with sick or dead birds before they fell ill, he said.

In Hunan where a girl died before tests could be done to determine the cause of death and her brother recovered from bird flu it was only after the children were ill that the authorities found out they had been exposed to sick or dead birds.

While there has been no report of avian influenza outbreaks among poultry in Guangxi this year, the region was the first to report poultry infections last year on January 27, 2004.

However, Ziyuan County, where the latest case was reported, neighbours Hunan Province, which has reported both human cases and animal outbreaks this year.

While it is ideal that animal outbreaks are detected early before they spread the infection to humans, it is difficult to trace isolated outbreaks in small farms, Wadia said.

There have been human cases in other countries where exposure to infected poultry was difficult to identify during the investigation, Roy said.

So far, there is no evidence that the H5N1 virus has acquired the ability to jump effectively or efficiently from human to human, the WHO stressed yesterday.

In another development, Vice-Premier Hui Liangyu said at a conference on bird flu in Asia that closer collaboration between countries is vital to combat the threat. At least 69 people have died of the virus, all in Asia.

(China Daily 12/08/2005 page1)