Waitakere Hospital staff have tested positive for Covid-19.
The three staff were working on a ward with patients who had been transferred from the CHT St Margaret's residential aged care home in Te Atatu.
Three of those residents died after being sent to the hospital. Now, Waitematā DHB has confirmed its own staff have caught coronavirus.
Waitakere Hospital has closed affected wards to further admissions and will undertake contact tracing to try to establish the source of the infections.
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"As soon as we became aware of these cases, we moved quickly to respond and we will take all appropriate actions to minimise any risks," Waitematā DHB Deputy CEO Dr Andrew Brant said.
"It is unclear at this stage whether contact with those patients was the source of the staff contracting Covid-19 or whether any of the cases are linked. Full personal protective equipment (PPE) was made available and worn by staff at all times in this area.
"The DHB has an auditing programme in place on the appropriate use of PPE for all Covid patients. An urgent review is in progress to understand how and where the infection may have occurred."
On April 17 ambulances transferred the first St Margaret's residents to Waitakere Hospital, with the DHB saying this "will ensure the residents receive the support they need while St Margaret's staff are cleared to return to work".
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Waitemata DHB staff continue working inside the facility and caring for remaining residents. The cluster is now linked to 20 cases of Covid-19.
As of yesterday there were 15 St Margaret's residents in Waitakere Hospital, including three who are Covid-positive.
Three residents transferred to Waitakere Hospital have died; the first on April 20, one on April 24 and another on April 26. All had underlying health conditions.
There are 34 cases linked to the St Margaret's cluster, with 11 recovered. The origin of the outbreak is still listed as "unknown".