Health officials say they have identified all the people who came into close contact with an outbreak of avian flu at a smallholding in north Wales.
Teachers and pupils at Ysgol Henllan have been given treatment
The number of people found to have had contact with the disease rose over the weekend to 142, of which 12 are being treated as being positive for bird flu.
The mild H7N2 strain of bird flu was first found last week among chickens at a farm near Corwen, Conwy.
Children at a Denbighshire school are being offered anti-viral medication.
A year five pupil at Ysgol Henllan suspected of contracting the virus has been linked to the smallholding.
A dozen children aged nine and 10 and two teachers at the school are being given tamiflu treatments as a precaution.
The National Public Health Service of Wales has said a total of 142 people have had either direct or indirect contact with the virus, which is not the virulent H5N1 strain of avian flu.
Twelve people are being treated as "positive", but no-one is seriously ill.
Of the 142 to come into contact with the virus, 47 came into contact "in the household setting," 14 in the school and 81 in "the workplace setting".
Health officials held a meeting for concerned parents at the school on Monday evening, in which it was stressed the risk of anyone contracting the virus is very small.
An outbreak was first confirmed at a smallholding in Conwy
Another meeting for those who could not attend is planned for Tuesday evening.
The National Public Health Service of Wales's director for north Wales, Andrew Jones, said it was "reassuring" so few people had reported symptoms.
He said: "We are treating 12 cases as positive.
"We always approach schools in a precautionary way.
"We are advising them that the risk to the population is low and that avian flu is a disease of birds.
"It would be very unusual for it to spread from person to person."
Hugh Pennington, a microbiologist and bird flu expert from Aberdeen University, added: "You have to be in quite close contact with infected birds to get infected.
"It doesn't spread from one infected person to another.
"It's still a bird virus - someone infected isn't going to cause any more human cases."
John Lloyd, who has two children at Ysgol Henllan, said he was satisfied the outbreak has been handled well by officials after attending a meeting with parents on Monday.
He said: "They felt it was all under control which confirmed what I felt to be honest.
"I think they've done enough to keep the public calm."
The first confirmed case involved a smallholding at Llanfihangel Glyn Myfyr, Conwy.
Owners Tony Williams and Barbara Cowling, who have tested negative for the virus, called in a vet after their Rhode Island Red chickens began to die.
They bought the chickens at Chelford Market at Macclesfield, Cheshire, some 70 miles (112 km) away, on 7 May.
A total of 30 chickens from the smallholding have now been slaughtered after 15 birds died.
Officials have stressed that the disease found at the Conwy farm was the H7N2 strain of bird flu, not the more virulent H5N1.
The second possible case emerged on Saturday about 35 miles (56 km) away, at a farm on the outskirts of Efailnewydd, near Pwllheli. It has also been linked to the market.