Young children and the elderly are particularly vulnerable to E. coli

Five cases of the stomach bug have been confirmed among children at Steps Ahead in Trowbridge, and another two are suspected.

The nursery has closed voluntarily for the rest of the week while the source of the problem is investigated.

All staff, children and their parents will be tested for the illness before it reopens next Monday.

'Cause unknown'

The county's principle environmental health officer David Bardwell said: "We are taking this very seriously because young children are involved.

"But there is no indication at this point that the problem has spread to anywhere in the community outside the nursery."

Mr Bardwell said the cause of the outbreak might never be known.

"We should be able to work out the first person or family where it started, but the likelihood is that we may never know what caused the illness as it could be one of any number of things," he said.

"From our point of view it is more important to help with prevention and protection, stopping the problem spreading."