One baby has died and fourteen others have developed septicaemia from what is thought to be a batch of contaminated drips.
Dr Paul Cosford, medical director of Public Health England, said he was confident the source of contamination had been identified.
"The good news is that the shelf life of this product is already passed," he added.
Meanwhile the 14 surviving babies are said to be responding well to treatment and are unlikely to suffer long-term consequences.
Video report by ITV News Health Editor Catherine Jones:
Questions have been raised over how a batch of intravenous fluid could potentially have become contaminated, after the death of one baby.
The suspected contaminated batch of a food supplement linked to the blood poisoning of 17 babies, was sent to 22 hospitals.