Aucklanders are being warned of a persisting COVID-19 problem that's worrying New Zealand's health authorities - "mystery cases" - and there are 29 of them, including two patients who presented at Middlemore Hospital.
Leading epidemiologist Michael Baker says he'd like to see "several" days of no mystery cases before Auckland adjusts restrictions.
In full PPE, staff at Middlemore Hospital's emergency department are on high alert.
In less than a week, two patients have walked through their doors with Delta. The most recent arrived on Thursday.
"There's a slight concern if they arrived into a waiting room area and for some reason, anyone wasn't wearing a mask then that would expose them to risk," Otago Uni epidemiologist Prof Michael Baker told Newshub.
The cases came to the ED for a non-COVID-related issue. They told staff they didn't have symptoms and hadn't been to locations of interest.
A test was taken as a precaution but before the positive result was known, the patient left.
Director-General of Health Dr Ashley Bloomfield confirmed any other patients are considered exposed.
"There were 30 other patients in the ED and short stay ward who have been assessed as being contacts. Of those 17 are in the hospital and have been isolated from other patients," he said.
And there's one unfortunate similarity with both the Middlemore cases - both patients spent time in the short stay unit which is part of the ED.
What's concerning health authorities is that neither case has been linked, meaning how they became infected remains a mystery.
Mystery cases are important as they could represent unknown transmission in the community.
There were 11 new cases on Friday, six of those are unlinked or mystery cases and the grand total of unlinked cases is 29.
Auckland University's Associate Dean of Pacific Medical and Health Sciences Dr Collin Tukuitonga said the mystery cases are "why I would be much more reluctant to move down a level".
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Professor Baker agrees saying a run of days without mystery cases is what's needed to dropdown.
"That's what we need to see is several days of no unexpected cases in the community," he said.
And to really know for sure, testing this weekend is critical.
Deputy Prime Minister Grant Robertson says testing rates do form part of the thinking around shifting alert levels.
"If testing numbers stay high and we're still seeing case numbers come down then we have a confidence that we really are capturing what might be out there that we don't know about."
Professor Baker's advice to Aucklanders is unequivocal - even if you have the slightest symptoms - "get tested".
Testing is what Middlemore's staff are doing more frequently now when patients turn up at ED.
The hospital and surrounding community have been at the epicentre of this Delta wave, but they're under extreme pressure.
Hospital beds are full and they're understaffed - a scenario that's considered entirely foreseeable.
Sarah Dalton, Association of Salaried Medical Specialists executive director, said it was "very predictable".
"Hospitals nationally have not been appropriately funded either in terms of facilities or staffing... If we had a more significant outbreak we would not cope."
Dr Tukuitonga said his "heart goes out to the team at Middlemore".
"They're doing the best job they can. I would have thought that they really need additional support and resources."
Middlemore is still 29 staff down, but the number of people arriving for care isn't slowing down.
Figures provided to Newshub by the Health Ministry & Counties Manukau DHB show the number of contacts from the two positive hospital related cases at have ballooned to 214.
So far seven family members of the first case have tested positive for the virus. Crucial day five test results for patients and hospital staff exposed to the first case are due back tomorrow.
