Up to 90 infant children are being tested for the most serious strain of E.coli after an outbreak at a north Wales nursery school.

Health officials have confirmed two youngsters are suffering from the 0157 strain of the bacteria.

The main symptom is bloody diarrhoea

E.coli expert Dr Davey Jones

They attend the Menai Nursery at the Parc Menai business complex in Bangor.

They did not require hospital treatment and are described as "currently well", but up to 90 other children who have attended the nursery in the past few weeks are to undergo tests.

The parents have been asked not to take their children to any nursery until their children have been screened.

Many strains are harmless, but the more serious ones can cause serious illness, including vomiting, diarrhoea and, in severe cases, intestinal bleeding. Most people recover within two weeks.

Dr Davey Jones, an E.coli researcher at Bangor University, said the 0157 strain seen in the nursery children was especially nasty.

"This particular strain has a very good capacity to cling onto the inside of the intestines, where it releases a toxin into the bloodstream," he said.

Serious strain : Dr Davey Jones

"That causes the intestines to bleed and the main symptom is bloody diarrhoea."

The E.coli bacteria exists everywhere in the environment but are commonly ingested by contaminated food.

Letters have been sent to parents stating that all children who have been at the nursery since the beginning of July are to be screened for infection - even if they have since moved somewhere else.

The nursery manager has declined to comment on the outbreak, saying they had to protect the confidentiality of the children.

North Wales Health Authority was expected to make an official statement on Tuesday, following a meeting of the local Outbreak Control Team.

One fact which has already emerged is that standards of hygiene were satisfactory at the nursery, though it remains closed while inquiries continue.

No comment

The team is made up of members of the health authority and Gwynedd County Council.

The environmental health officer dealing with the case, Gwenan Williams, said she was not in a position to go into great detail.

"Any case of any infectious disease is worrying, but I'm not in a position to confirm anything at the moment".

North Wales was last in the news because of E.coli more than two years ago, when 17 people contracted the bug after visiting a farm tourist attraction at Brynsiencyn on Anglesey.

E.coli exists everywhere in the environment

And in Scotland, a current outbreak of E.coli 0157 at a caravan park in the Highlands has affected a total of 15 people.

Scottish health officials said on Monday the number of probable cases had risen to 12, with three children confirmed as suffering from the bug.

All of those stricken by the bug have been in contact with the Rothiemurchus Caravan Park at Coylumbridge, near Aviemore.

Householders and businesses in the area were advised to use boiled or bottled water while attempts to isolate the outbreak continued.

The outbreak was confirmed on 1 August and experts said they believed a private water supply may have caused it to spread.

It was thought that the downpours which swept across Scotland last week could have washed manure or other substances into what would normally have been a safe water system.