Up to 2000 babies including some in the Lakes and Bay of Plenty regions have been recalled to hospital to have their hearing checked after the Ministry of Health discovered "irregularities" in its national newborn screening programme.
One of the babies recalled, a 10-month-old boy, was found to have a congenital hearing defect.
Officials would not say what the irregularities were, but it is believed the hearing of some newborn babies was not checked.
It's understood some screeners from the six affected district health boards were testing themselves instead of the babies.
Six boards - including Auckland, Waitemata, Bay of Plenty, Lakes, Hutt Valley and Canterbury - were found to have irregular screening results, and two, Waikato and Hawke's Bay, are still providing information.
Associate Health Minister Jo Goodhew said she was "very concerned" when she was told in July of the situation.
Asked if any workers had been dismissed or stood down, she said: "I am aware a number of screeners no longer work at the DHBs."
Two boards told the Health Ministry five months ago they had concerns about their newborn hearing screening programmes.
National Health Board national services purchasing director Jill Lane said that as a result the Ministry initiated a review of all DHB newborn screening activity.
It is not known how long the issues had been going on or how old some of the babies are now.
Ms Lane said a report into the investigation was completed this week, but its recommendations would not be made public until it was sent to affected families early in the New Year.
Ms Lane did not know how many of the 2000 families sent recall letters had responded, but said that of those that had, the 10-month-old was the only delayed diagnosis.
Mrs Goodhew said while that family would be disappointed, they were now getting the support they needed at birth.
"I understand there are no waiting lists for cochlear implants. Children have priority so that child will have cochlear implants if that's what he needs."
The programme is intended to check the hearing of the 60,000 babies born each year.
All babies are supposed to be screened within a month, to complete an audiology assessment in three months and start any required treatment by six months.
"We want to pick up any irregularities in a child's ability to hear as early as possible," Mrs Goodhew said.
About 2000 babies a year need further hearing assessment, and the programme expects to find one baby in 1000 with congenital hearing loss.
Mrs Goodhew said she would not pre-empt the report by giving details.
"It's certainly not what you want. You want a standard of screening and you want everyone to conform to that standard and in this case it hasn't happened."
She said she had more confidence in the programme now a thorough investigation had been made, and she was comfortable with the "comprehensive recommendations".
The country had about 115 technically trained screeners.
- NZ Herald