Medical tests carried out on pupils at a south Wales primary school have failed to identify a suspected victim of E.coli.
Glenboi primary in Rhondda Cynon Taf was closed last Friday after the discovery of bloody diarrhoea in the boys' toilets - a symptom of the illness. Parents were given kits to test their children's stool samples at emergency meetings held by health officials last weekend.
However, none of the pupils has fallen ill, although several have tested positive as carriers.
As TES Cymru went to press, 60 of 97 children at the school had provided negative samples. Most of the rest have not yet been tested, with the remainder testing positive as carriers.
A third of people who pick up the infection will display no symptoms and will not fall ill, although they are contagious.
Health officials will now investigate how the pupils came to be carrying the germ. A school spokeperson said: "More of the children will come back as they test positive and are eliminated - until then we are just trying to get on as normal."
As of Wednesday, there had been no new cases of children developing E.coli for 15 days, and the total numbers affected stood at 156. So far the outbreak has caused one death and affected children in 42 schools across four counties in south Wales.
Health officials were criticised for not closing the affected schools after the first cases were reported in mid-September.
However, a spokesperson for the outbreak control team saidsaid: "The risk of an unknown ill child with bloody diarrhoea in Glenboi school was considered sufficient to justify closure."
Five-year-old Mason Jones, a pupil at Deri primary school in Bargoed, died at Bristol Children's Hospital last week from renal failure caused by E.coli. Police have since launched an investigation, and an inquest into Mason's death was opened and adjourned in Bristol on Tuesday.
Meanwhile, the children's commissioner Peter Clarke is to collect evidence on the standard of school dinners across Wales.
Last week it was reported that the strain of E.coli responsible for most of the cases had been found in samples of meat from John Tudor Sons, a Bridgend butcher and meat supplier.
Welsh Assembly members will decide next Tuesday which of them will be represented on a committee to draw up terms of reference for a public inquiry.