A special type of blood test could give vital clues as to how an isolation hotel maintenance worker got Covid-19 from a woman he had never met.
A lab technician holding blood tube test. Photo: 123rf.com
Health officials are stumped by the case and are being urged to use serology testing which could reveal if a person has had the disease even if they haven't had a positive Covid test.
It could show if a third person is the missing link between the worker and the infected woman isolating in the hotel.
And some scientists are now pushing for the blood testing to be rolled out to thousands of border workers to more accurately map the spread.
The blood test is more commonly known as a serology or antibody test.
It cannot diagnose someone with an active Covid-19 infection, but it can confirm if they have had the virus in the past - even if the person was asymptomatic or had mild symptoms.
Public health professor Michael Baker said the test would be useful to map how the virus spread from the woman to the maintenance worker at Rydges Hotel two weeks after the infected guest had left - and the pair had no physical contact.
"They appear to have been infected with a Covid-19 virus of the same genetic lineage.
"So it does suggest very strongly that that was source infection for this case, but then you want to reconstruct what happened between the person staying in the hotel and this maintenance worker being infected."
University of Otago epidemiologist Professor Michael Baker Photo: University of Otago Wellington / Luke Pilkinton-Ching
Doing the serology testing on all Rydges Hotel staff would show if other people who had missed out on Covid testing had been exposed to the virus, Baker said.
"You really want to know whether other staff involved who might have been passed the virus on perhaps asymptomatically to this maintenance worker, or were they infected potentially from a contaminated surface there.
"It has real implications for how we manage these facilities.
"So this would be a situation where it would be justifiable I think, to use serological tests and to try and reconstruct that line of transmission."
Prior to the second Covid wave more than 60 percent of border staff had never been tested.
Immunologist Nikki Moreland said the serology testing could paint a broader picture of what was going on at the border and at the Rydges Hotel.
It would give clues about transmission where swab testing had not been able to.
"I think it could help to understand where the virus might have been in people that we haven't detected it with through normal surveillance mechanisms.
"That could be particularly useful in people that may have very mild symptoms and aren't even really necessarily aware that they've been exposed or infected," she said.
The Rydges Hotel, which is being used as a managed isolation facility, in Auckland. Photo: RNZ / Dan Cook
Clinical microbiologist Dr Arlo Upton said health officials might get more clues about the Rydges case and the community cluster if all border staff take the blood test as well as the regular Covid swabs.
"Although it would be perhaps a little bit logistically difficult, it's my belief that it would be worth offering serological testing to people who have been working around the border in recent months to provide us with a little bit more information around what's happened with the recent issues."
Dr Arlo Upton said contacts of the family at the centre of the community cluster should also have the blood test to see if the infection was already circulating before the first known infection on 31 July.
Dr Gary McAuliffe, medical director at the laboratory Labtests agreed.
The tests could play a crucial role in providing answers to the origins of the outbreak, he said.
"Where serology really has its value is outside the first week or two of symptoms where somebody may not be PCR positive anymore, but serology may play a key role in picking up if someone's had exposure in the past and helping to link back to previous cases."
He said the testing should be part of the government's border control plan.
University of Auckland microbiologist Siouxsie Wiles said Rydes Hotel case was a real mystery and showed not only the importance of testing, but that daily health and symptom checks were not infallible.
"This virus is so tricky, some of the symptoms are very much like like lots of things, they can mimic asthma and all sorts of things.
"It's a real mystery" - Auckland University microbiologist Siouxsie Wiles
"So the question is, is it possible to stand down people every time they have one little symptom that matches ... and ensure they still got paid?
"Or are there quicker tests that are coming on line that would allow that rapid, at the point of a person turning up, can you do a quick test... It may be those are not as sensitive but you might pick up a case like this one."
The serology test, though not showing whether a person had a particular strain of the virus, could provide a place to start, where CCTV footage could be looked at again and interviews carried out to try and determine whether there had been an overlap.