Eleven of the 36 people, all of whom are in Wales, have symptoms of flu or conjunctivitis, but the National Public Health Service for Wales stressed that no one is seriously ill.

Dr Marion Lyons, lead consultant in communicable disease control with the NPHS said: "We believe the risk to the health of the general public is low."

She described the H7N2 strain identified at a farm in Corwen as "very mild" compared to the more virulent H5N1.

The case was confirmed last week after 15 Rhode Island Red chickens bought by the farm's owners at Chelford Market, Cheshire, died. A further 30 birds have now been slaughtered.

Tests have been carried out at a farm on the Llyn Peninsula but the results are yet to be released.

Dr Lyons said that the possibility of person-to-person contact could not be ruled out.

She said: "Person-to-person spread would be very unusual but limited spread of this type has been seen elsewhere in the past in some cases of bird flu. There is no laboratory confirmation."

The NPHS defined possible contacts of bird flu as those who had been in contact with affected premises or infected poultry. It also includes people who have had close contact with another person with confirmed or suspected bird flu.

Dr Lyons added: "Of the people with conjunctivitis or a flu-like illness, some did not have close contact with infected poultry."