The Herald understands ED nurses were told they should still go to work, as the person who later tested positive was vigilant and wore personal protective equipment (PPE) when on site.
The staff member said some nurses with vulnerable people or children in their household bubbles were concerned, and wanted more information from authorities.
"From those who I am talking to, they are concerned about their safety."
They understood staff would from now have to wear N95 masks, not the surgical masks they'd previously been using.
Another source understood the person who tested positive was linked to the Māngere church sub-cluster in the ongoing Delta variant outbreak.
The DHB said the emergency department at the hospital in Ōtāhuhu, South Auckland, was still open.
The staff member was asymptomatic and fully vaccinated. As a precaution, the staff member was stood down and public health staff were investigating.
A Ministry of Health spokesman said the case was detected through routine testing.
The New Zealand Nurses Organisation (NZNO) said routine testing meant many healthcare workers had Covid tests more frequently than the general population.
Kerri Nuku, NZNO President and Kaiwhakahaere, said the staff member was understood to have been asymptomatic and vaccinated.
She said N95 coverings were known to provide better protection than other face masks, but supply problems seem to have hampered distribution of N95 masks to workers.
She said a recent NZNO survey found 59 per cent of members were concerned these masks weren't as freely available as they should be.
Nuku this evening said availability of other PPE items for nurses seemed to be adequate.
The union supported members going back to work at Middlemore, she said.
"Healthcare workers will continue to practice in a safe way. It's a safe place to be. It's just that we're all hyper-vigilant."
She said one area where safety might be enhanced was in pod rostering.
This involved specific teams of staff working with specific patients.
Pod rostering meant staff would limit contact with other healthcare workers, so if one team member fell ill, that pod was stood down and another filled the roster gap.
Other healthcare unions, representing thousands of staff, have recently said pod rostering was needed for essential workers.
"All staff have been asked to wear full PPE and all patients have been given masks," another DHB staff member said today.
"They are starting to set up sign-in stations at all entrances."
- Additional reporting: Newstalk ZB
