School is still shut as tests continue.
Abercynon Infants School remained closed after public health officials decided all 64 children should be tested for the bug.
The checks follow the discovery that four children at the school have contracted food poisoning.
The school was closed at the weekend and will only be reopened when all the youngsters have been cleared of the infection.
The e.coli outbreak - the worst in Welsh history - has now affected 159 people, mostly young children, and led to the death of a five-year-old boy.
The Welsh Assembly Government has promised a 'no-holds-barred inquiry' into the outbreak which is hoped to get underway in January.
Dr Carl Clowes, of the Wales Centre for Health, said the inquiry should follow food from the Bridgend meat firm at the centre of the outbreak to school canteens.