The result came from a regular influenza virus surveillance in pigs conducted by the University of Hong Kong (HKU) at Sheung Shui Slaughterhouse from February to April.

Under the programme, pigs at the slaughterhouse were tested by blood, tracheal and nasal swabs twice a month.

A CFS spokesman said given the wide transmission of the pandemic H1N1 virus in humans, detection of the virus in pigs would not be a surprise. It was expected that positive findings might appear from time to time in the surveillance programme in future.

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

"The FEHD inspects the certificates and health of the imported pigs at the boundary control points. Pigs also have to go through ante-mortem and post-mortem inspections in the slaughterhouses. Only pigs that pass the inspections can be supplied to the market and sold for consumption," he said.

The CFS has been in close liaison with the Chinese mainland authorities over any abnormal situation concerning mainland farms supplying live pigs to Hong Kong, and farm inspection would be stepped up as necessary, the spokesman added.

He said CFS would continue to monitor reports of the HKU surveillance program and make announcements on a regular basis. Results will be announced immediately if there are significant public health impacts such as genetic reassortment of viruses.