According to The Standard, the center said the positive sample was found from among 1,500 pigs at the Sheung Shui slaughterhouse during a regular surveillance programme that took place from mid-October until January.

It added that the virus, which caused the 2009 pandemic, does not pose any public health or food safety risk.

The center said 27 samples which contained the swine flu virus had also picked up some genes of the human swine influenza virus.

From these samples two were detected as having the swine influenza H3N2, while the remaining 25 samples had H1N2.

University of Hong Kong microbiologist Malik Peiris is in charge of the surveillance programme.

He said the detection of the pandemic H1N1 virus in pigs is not a surprise, given the wide transmission of the pandemic virus in humans.

Positive findings might continue to appear from time to time in future.

"There have been similar reports from many parts of the world," Dr Peiris said.

"These showed that swine influenza viruses carried the genes of the human swine influenza virus, and are unlikely to pose any major human health risk or cause problems in food safety."

Under the regular influenza virus surveillance programme for pigs, the center has been helping Hong Kong University researchers obtain blood and tracheal and nasal swabs from the slaughterhouse twice a month.

The center will continue to monitor reports of the university programme.

Announcements will be made regularly.

If there is a significant impact on public health, an announcement will be made without delay, a spokesman for the center said.

According to the World Health Organization, the World Organization for Animal Health and the Food and Agriculture Organization of the United Nations, human swine flu cannot be contracted by eating pork and pork products that are handled properly and thoroughly cooked.

The spokesman said that all live pigs imported from the mainland come from registered farms and are accompanied by animal health certificates issued by the mainland authorities.