Health experts have said Watford has been classified as a swine flu “hot spot” to help stop the spread of the virus.

Pupils at more schools across south west Hertfordshire have this afternoon been sent home with letters informing parents of outbreaks of the bug in classrooms.

Watford, Three Rivers and Hertsmere have all now been classified as epicentres for the virus, joining areas across London, near Birmingham and in Luton as those most severely infected.

A statement from the West Hertfordshire PCT read: “The Department of Health and the Health Protection Agency (HPA) have identified several areas in the UK where there is now widespread community transmission of swine flu - these are sometimes referred to as 'hotspots'.

“These areas now include the Watford, Three Rivers and Hertsmere district council areas in West Hertfordshire.

“In the same way as has already been done in parts of the West Midlands and London, the HPA has issued updated guidance to GPs in West Hertfordshire on how to handle cases of swine flu.

“From now on, GPs in these 'hotspots' will be using clinical assessment to determine who needs to be treated.

“This means that people who have flu-like symptoms may be clinically diagnosed as having swine flu without needing laboratory confirmation in all cases. GPs will then assess whether treatment is appropriate.”

Dr Jane Halpin, director of public health in Hertfordshire, said the decision should help prevent the spread of the bug.

She said: “We have always known that this virus would spread and have been monitoring the situation closely adjusting our approach when necessary.

“The approach we have taken up to now has been vital in slowing the spread of swine flu but as there is now a significant level of transmission within parts of west Hertfordshire, it is appropriate to make these changes.”