Four people have tested positive for bird flu linked to a low-risk strain found in chickens which died on a farm in north Wales, as samples were being taken Saturday from another farm in the area.

Doctor Christianne Glossop, chief veterinary officer for Wales, has said that the chickens at the first farm died from the H7N2 low pathogenic avian influenza strain, not the most virulent H5N1 strain.

The Health Protection Agency (HPA) "confirmed infections in four" of the samples taken from nine people who were associated with the infected or dead birds and reported flu-like symptoms, its chief executive Pat Troop said.

"These test results confirm that human infection with the avian flu virus has occurred. The cases so far have been associated with the infected birds," Troop said.

She stressed that the H7N2 avian flu remains largely a disease of birds and does not transmit easily to humans.

Three of the nine people were treated in hospital but were later discharged.

The National Public Health Service for Wales and HPA officials are following up all close contacts of the individuals who have been ill as a "precautionary measure."

Meanwhile, experts are taking samples from birds at a farm in the Llyn Peninsula in north Wales which has links to the market where the original birds were bought.

The last case of bird flu in Britain was an outbreak of H5N1 in February at a turkey plant in eastern England.

Nearly 160,000 turkeys were culled as a precaution in the country's first major outbreak of the potentially lethal virus.

The H5N1 strain of bird flu has infected at least 306 people worldwide and killed around 185 of them, mostly in southeast Asia, since the end of 2003, according to World Health Organisation figures.