Covid-19 Omicron outbreak: Auckland and Northland Covid case numbers believed to be double what testing shows

Health officials believe testing is only picking up half of the total positive Covid-19 cases in Auckland and Northland.

It comes as the head of one of Auckland's most prominent health and welfare providers suspects as many as two-thirds of positive results aren't being reported.

On Friday, a spokesperson for the Northern Region Health Coordination Centre (NRHCC) told the NZ Herald it was estimated about half of all positive cases were being discovered.

"Estimating the true prevalence of infections versus identified cases is very difficult.

"Our current best estimates, based on our patterns of cases compared to overseas experience and looking at our testing coverage, are that we are accounting for approximately half of all actual cases."

Across Northland and Auckland's four district health boards, it was estimated 96,275 people - or 5 per cent of the total population (1,925,500) - had Covid-19 as at Friday.

The northern region registered 8005 cases on Friday - Auckland: 7240, Northland 765. It was a marked decrease from the 13,767 tests a week prior - Auckland: 13,252, Northland 515.

The NRHCC spokesperson stressed the estimation wasn't confirmation that thousands of people weren't reporting their positive test.

"Unaccounted cases are likely to be asymptomatic, which also means they're less likely to pass it on," the spokesperson said

"We have also heard of people who have not registered their positive test result but are isolating and following the rules regardless."

There would also be those who had symptoms, but would continually test negative through fallible rapid antigen tests - now the most common form of testing.

Rapid anitgen tests aren't always accurate. Photo / Bevan Conley

It was a point raised by director general of health Dr Ashley Bloomfield at yesterday's Covid-19 update when he referenced the limitations of rapid antigen tests in being unable to detect every positive case.

"We are seeing people, even if they are in households with other cases, they can be returning not just one but sometimes several negative tests and then a positive test, or some of them [are] symptomatic and never return a positive test but probably were Covid cases," he said.

"All this does is emphasise that rapid antigen tests are one tool but if people are symptomatic, they should remain home.

"If they've been exposed and particularly if they're a household contact and have symptoms, they should assume that they do have Covid."

Despite the NRHCC data, Bloomfield said he had been impressed and surprised by the number of people reporting their test results.

Director general of health Dr Ashley Bloomfield. Photo / Mark Mitchell

He confirmed the Ministry of Health would be publishing positivity rates for rapid antigen tests by district health board from today, which would indicate what regions were further burdened by the virus.

Last week, Auckland health officials tentatively predicted Tāmaki Makaurau had reached its Omicron peak and daily case numbers wouldn't increase.

NRHCC chief clinical officer Dr Andrew Old accepted this prediction was limited by the level of unknown cases in the community, but he said testing data indicated the peak had been reached.

"Although we don't have a really good sense of the total number of infections out there, we do know that our testing seems to be consistent, so we would be cautiously optimistic that the number of cases we are seeing represents a true flattening."

Old said he would be confident in determining whether Auckland's Omicron outbreak had peaked in a few weeks.

Papakura Marae chief executive Tony Kake, who had co-ordinated health and welfare support for thousands of positive cases in South Auckland, estimated between half and two-thirds of all cases weren't being reported.

Papakura Marae chief executive Tony Kake. Photo / Michael Craig

He guessed contributing factors to this were people weren't sure where to report their test results or they were reluctant to get tested as it would mean time off work.

"That's my gut feeling," he said,

"Whilst we might be able to supplement kai through our food bank, it doesn't pay the rent, it doesn't pay the power."

He was pleased the isolation period for cases and household contacts had been made consistent at seven days, which reduced confusion.

"You've got it or you haven't, or you're a contact or you're not and that's how simple they've got to keep it."

However, he did suspect some people were keeping their infection from their employer, in the fear of losing their job.

On Friday, 25 of Kake's 82 staff were isolating either as positive cases or household contacts.

For any staff impacted by Covid, Kake did not deduct their isolation period from their sick leave.

He hoped the Government and other employers would look at a similar process, so people with little sick leave weren't encouraged to hide their test results or avoid testing.