Frances Blacklock's son Mason had been delivered by Caesarean section in February 2012, and was taken to another hospital to have surgery to correct a bowel problem diagnosed while he was in the womb.
But soon after he was brought back to UCLH (University College London Hospital), he suffered a heart attack, which investigators later found was due to excessive magnesium in his IV feed.
After the incident, hospital staff phoned Frances, 27, who rushed in only to discover her son on a ventilator, looking weak and 'grey' - which nobody could explain.
The mum-of-two was then told that police would investigate the incident because of fears her son was poisoned. It took a year-long probe by police and medical investigators to conclude that the feed had been to blame.
Frances told the Evening Standard: "The investigation was awful, even my partner and I had to be eliminated from suspicion. To be involved in something like that was just heartbreaking, especially when all we cared about was Mason getting better.
"Mason is now two and a half and, while he needs regular appointments at UCLH to check his progress, he is on his way to what we hope will be a full recovery."
She has also called for safety regulations to be overhauled.
She said: "We want to know how these problems happened and what is being done to prevent them from happening again."
David Body, a lawyer at solicitors Irwin Mitchell, who represent Frances and her son, said: "The recent reports linking feed contamination to the death of a child have shone a spotlight on this issue and the products that vulnerable patients are administered during hospital treatment.
"Our work on behalf of Mrs Blacklock means we understand the ordeal undergone by parents when an event like this happens and the uncertainty about the long-term consequences this can have on affected children."
A UCLH spokesman said: "Mason came to us as a very sick baby and when he was six days old his condition deteriorated rapidly.
"Due to the astute intervention of our clinical team, this was discovered to be due to high levels of magnesium in Mason's blood.
"We are pleased that our swift intervention saved his life. We are in regular contact with Mason's family - who have nothing but praise for our care - and are delighted that he has grown into a healthy two-year-old boy."
A Quest Healthcare spokesperson said:
"Quest Healthcare has had no communication from Mr and Mrs Blacklock's solicitors, Irwin Mitchell, of any kind about the issues raised in their press release. Quest Healthcare was not provided with a copy of the MHRA/Police report into this incident and so cannot comment on its content.
"But there was no issue raised at the time of any liability on the part of Quest Healthcare for any medical issues concerning Mason Blacklock; nor was any such issue raised at the time by the Blacklock family or their solicitors who expressed satisfaction with the outcomes.
"Fifty five bags of the same batch of the food was supplied by Quest Healthcare and no problems of any kind were reported, and no subsequent issues have been raised about any of their products."
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