A man whose daughter is one of four E.coli cases at a south Wales valleys infants school said the youngster is "out of sorts" but starting to recover.
Teachers will stay at the school but pupils must be tested to return
The man and his wife were among the first parents to attend Abercynon infants on Sunday to meet public health officials dealing with the outbreak.
He said his daughter was "off colour" but otherwise not particularly unwell.
He said: "If my wife had not picked up on it, we might well have overlooked it."
The couple, who did not want to be identified, said they suspected something was wrong last Wednesday when blood was found after the girl had been to the toilet.
The next day the sample was taken for testing, but none of the girl's samples tested positive for E.coli until last Friday.
Even so, he insisted that his daughter was not as unwell with the bug as he might have thought.
"We thought with it being E.coli there might have been more to look for, but she has just been a bit off colour," he said.
The man's daughter is one of 64 children who are being kept away from school while tests are carried out to see who else might have the bacteria.
Public health officials are convinced the new cases, although part of the outbreak which has affected 159 people, mostly children, are not caused by the primary source of the infection - school dinners.
Julie Lane is confident the outbreak is being handled properly
That is why they are asking for the parents' help in identifying the network of person-to-person contacts which could have led to the infection reaching the school from one of the other 42 infected schools.
The parents who visited the school on Sunday were given plastic pots in which to collect a sample for testing. Youngsters who test "clear" for two tests at least 48 hours apart will be allowed back to school.
Many parents expressed confidence in the way the outbreak had been handled, although some plan to keep their children away for a few days.
Julie Lane, a health authority worker, with a six-year-old daughter at the school, said: "I think the school is doing the right thing and we're all going to work together.
"People panic, but I think if we keep level-headed and work with the health authority we will get there."
Helen Jones, who has a son in Year Two, said she wanted him to return to lessons as soon as possible.
Anthony and Anne Bevan are to keep their daughter home
She said: "I found out about it on Tuesday when he came home from school and said there were only 10 in the class that day. They usually have over 20.
"They have taken the right action, there is anti-bacterial soap in the toilet and the sandpit has been taken away. The school is kept remarkably clean, the caretaker does a very good job.
"When his (my son's) tests come back negative, they will allow him back in to the school.
"If he is being moved from place-to-place, there is an increased risk of him catching it. At school, I know where he is."
Anthony and Anne Bevan have a six-year-old daughter at the school. Mrs Bevan said: "I have been keeping her home. Everyone is panicking a bit - she won't be going in next week at all.
Abercynon Infants School chair of governors, Victor Lloyd-Nesling, said he understood that all four children at the school were "on the mend".
"A lot of the parents are reassured by what they have heard - that everything that could be done is being done," he said.