Bulgaria is facing a nationwide H1N1 pandemic that could potentially affect as much as half the population, according to the Health Ministry.

Medical authorities, however, have refrained from dispatching an all-out warning because the "threshold" needed for that to happen is 200 people infected in every 10 000  although the situation is slowly but irreversibly deteriorating across Bulgaria.

The worst affected regions in the country are Yambol, Shoumen, Pleven, Lovech, Bourgas and Gabrovo, with big cities like Sofia, Plovdiv and Varna also registering increasing cases of the new influenza, according to Dr Angel Kunchev from the contagious diseases department in the Health Ministry, quoted by Dnevnik daily.

An emergency "holiday" was introduced in schools in Tryavna on October 28 with as many as 250 students potentially affected, by either swine flu or its seasonal equivalent.

"Because the town is small, the community is tight and contacts are intense and frequent, we advise people to abstain from any unnecessary interaction at all cost," Kunchev told Dnevnik.

"Six students are confirmed to have contracted the H1N1 virus in Tryavna, which is enough because in such circumstances, it is the dominant virus that usually affects the others in 90 per cent of the cases, and H1N1 is definitely the dominant one in this case".

Meanwhile, in Yambol, the situation was significantly worse in the secondary school of mathematics where 247 "confirmed and tangibly sick children" carried on attending classes and interacting with fellow pupils in spite of their condition.

"We have 247 out of 800 students confirmed sick, and they still came to school. We kept telling people that, should they experience the virus, they should remain at home and avoid contact," Kunchev said.

"We uphold the advice from the World Health Organisation that whenever someone displays symptoms of flu, regardless if its seasonal flu, it should be regarded as swine flu and extreme precautionary measures should be implemented," he said.