All contacts of the three Waitākere Hospital nurses with Covid-19 have been offered testing, with one already deemed a probable case.
So far 10 cases have been linked to the hospital in west Auckland including three nurses who had been treating six coronavirus patients from St Margaret's rest home.
The nurses are in isolation and 57 staff members they had contact with have been stood down over the risk of infection.
Director-General of Health Dr Ashley Bloomfield said today all 57 staff members and the nurses' families had been offered testing.
One person, a family member of a nurse, was a probable case, he said.
An audit is under way to investigate what the source of infection was for the three nurses.
Dr Bloomfield said a review due by Friday was being carried out by senior staff within the DHB and Waikato DHB's director of nursing as an independent.
It was hoped the review would offer insight into how all district health boards could strengthen their protocols and reduce the risk to front-line health workers, he said.
Waitematā District Health Board has previously told the Ministry of Health all staff had access to PPE (personal protective equipment) and wore it at all times when caring for the infected patients.
One nurse who works at the DHB said PPE [https://www.rnz.co.nz/news/national/415623/beggars-belief-that-ppe-would-fail-waitemata-dhb-nurse "wouldn't be 100 percent foolproof, but it certainly would be very, very effective", and it was hard to believe the PPE itself would fail.
However, she said the DHB's communication about PPE and its use and fitting of full-filter N95 masks had been poor.
The Ministry of Health said today the St Margaret's cluster has had another five cases newly linked to it.
They were not new cases, but investigations had proven these existing cases were linked to the cluster. They are not patients at Waitākere Hospital.