With 13 kids in hospital and 37 sick after visiting a UK farm, Health Protection Agency chief executive Justin McCracken has phoned parents of the children most seriously affected to apologise to them.
"If this information had been taken into account on 27 August, then the advice given and the steps taken on 3 September would have been introduced earlier and the farm might have been closed earlier.
"I wanted to speak personally to the parents of those children who are most seriously ill in hospital to explain what has happened and, however inadequate under the circumstances, to apologise.
"The position they find themselves in is unbearable and it is of course worse that what has happened might have been avoidable."
The farm was closed on Saturday – although the first E.coli case was reported on 27 August.
A pair of two-year-old twins, from Paddock Wood in Kent, have suffered acute kidney failure.
Initially, the HPA said the first case came to light on 27 August.
It later emerged that the agency had received a report of two cases in the previous week.