HUNDREDS of school children have been struck down by a flu bug.

Symptoms of the seasonal virus include fever, sore throat and headache. Some pupils have also complained of earache, nausea and diarrhoea.

Pupils of all ages in Darlington and the surrounding area have been affected. Some teachers have also gone down with the bug.

Parents have been sent letters asking them to keep their children off school if they are ill to prevent the infection spreading any further.

The Northern Echo understands that over the past few days more than 100 pupils have been absent from Longfield and Hurworth secondary schools and more than 50 have missed school at Heathfield Primary, all in Darlington.

Other schools across the town have been affected, including Abbey Infant and Firthmoor Primary.

Yesterday, the Health Protection Agency (HPA) said it had been made aware of high levels of sickness absence because of flu-like symptoms in a number of schools in County Durham and the Tees Valley.

It said the sickness was thought to be due to the usual mixture of seasonal viruses that circulate this time of the year.

But laboratory tests carried out on three pupils from a secondary school in Darlington were confirmed as influenza B, known to be circulating in several parts of the country at the moment.

Influenza B is less common than influenza A and often affects children. It is not related to pandemic or avian flu.

The HPA said people were not contacting their doctors about the illness, so it was hard to say whether other flu-like illnesses were influenza B, or not.

Dr Deb Wilson, of the County Durham and Tees Valley health protection unit, said: "We have advised schools that people who have been ill with these symptoms should stay away from school until they are well enough to return, unless they have had diarrhoea and vomiting, when they should be excluded from school until 48 hours after their symptoms have stopped."

She added: "As with any flu-like illness, people with symptoms should stay at home, rest, drink plenty of fluids and take paracetamol if necessary."

A spokesman for Darlington Borough Council, said: "The council is monitoring the situation."

Yesterday, Durham County Council and Redcar and Cleveland, Stockton and Hartlepool borough councils said there had not been any sudden increases in illness.

A spokesman for Durham County LEA said: "There are one or two schools where kids have been off with winter vomiting, but that is what we would normally expect at this time of year."

A Hartlepool Council spokesman said: "Like any town we've got children off, but we don't have any mass absence here in Hartlepool."

While a spokeswoman for Stockton council said: "There's a normal amount of kids off with coughs and colds, but nothing that makes us think it's something major."

Middlesbrough Council and North Yorkshire County Council did not comment