Four people have tested positive for a mild strain of bird flu which was first detected at a north Wales smallholding, the Health Protection Agency has said.
Thirty birds from the smallholding have been slaughtered
A 1km restriction zone remains in place around the farm in Conwy after the "low pathogenic" H7N2 strain of bird flu was found in chickens which died there.
Tests were carried out on nine people associated with the incident, with the five other people testing negative.
Three of the nine were taken to hospital but have now been discharged.
Health officials have stressed the disease found was the H7N2 strain of bird flu, not the more virulent H5N1.
In almost all human cases to date, the H7N2 infection has generally been associated with a mild disease and the risk to the general public is considered to be very low, they added.
The five people who tested negative are being treated as having had the virus as a precaution.
Two of the four who tested positive were from Wales and the other two were from north-west England.
The owners of the smallholding, Tony Williams and Barbara Cowling, have tested negative.
However, officials said this did not mean they had not been exposed to the virus, and further investigations were being carried out on their specimens.
Professor Pat Troop, chief executive of the Health Protection Agency (HPA), said those who were associated with the infected or dead birds and had reported flu-like symptoms were tested "as a precaution".
"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," Prof Troop said.
"It is important to remember that H7N2 avian flu remains largely a disease of birds. The virus does not transmit easily to humans.
"Worldwide, almost all human H7N2 infections documented so far, including those associated with this most recent incident, have been associated with infected poultry."
Dr Marion Lyons from the National Public Health Service for Wales said the source of the outbreak was clearly identified as the chickens on the smallholding, which had all been culled.
"For most of the people we have found with symptoms, the illness has been mild.
"We are contacting everyone who has been in close contact with the people who are ill so people who are not contacted by us should not worry.
"As is usual, we would advise anyone who is concerned about their health to consult their GP."
Chief Medical Officer for Wales, Dr Tony Jewell, said: "I would like to reassure the general public that the risk to their health from this outbreak is very low.
"This particular strain is not highly pathogenic and is normally only contracted following close contact with infected birds. In addition the symptoms are generally mild."
All people known to have been in contact with the infected birds, or to have visited the farm, have been given anti-viral drugs.
The bird flu was confirmed at the farm at Llanfihangel Glyn Myfyr, near Cerrigydrudion on Thursday.
The owners had bought 15 Rhode Island Red chickens two weeks ago, but all the birds had since died.
Samples from the dead birds were first sent for testing on 17 May, and 30 others on the site were later slaughtered.
Wales's chief vet, Dr Christianne Glossop, said it was a "top priority" to find the source of the disease.
This is the first confirmed case of bird flu in Wales.
There are various strains of the bird flu virus, with the H5N1 strain posing a risk to human health.
In February, more than 160,000 birds were slaughtered on a Suffolk farm owned by the Bernard Matthews firm after an outbreak of the H5N1 strain.
Avian flu was found there on 3 February and 2,600 turkeys died from it - a further 159,000 birds were then culled.
The Department for Environment, Food and Rural Affairs (Defra) would like to hear from anyone - who has not already been contacted - who purchased from or supplied to Chelford Market, Cheshire on 7 May, or any poultry keeper who visited Chelford Market on that day whose birds have subsequently become ill.
They are asked to contact their local Animal Health Office, details of which can be found on the Defra website or by phoning the Defra helpline on 08459 33 55 77. Lines are open between 0900 BST - 1700 BST seven days a week.