Coronavirus Covid-19: Three things that could give us more certainty

What are the signs that could give more certainty health officials managing the latest flare-up? Science reporter Jamie Morton explains three of them.

More zeroes – or key cases

Further negative test results outside MIQ would obviously prove encouraging.

Already, there’s cause for optimism: 12 of 42 close contacts of the family at the centre of the scare have returned negative results.

Test results of seven of nine close colleagues of the mother – who works at airline food and laundry provider LSG Sky Chefs – have also come back clear.

Director-General of Health Dr Ashley Bloomfield said negative test results of all of those close contacts would “reduce the likelihood” that New Zealand had a community outbreak on its hands.

But wider testing at Papatoetoe High School, where the daughter attended for a day, and in the community, where 3000 tests were carried out yesterday, was just as important.

Few – if any – cases in the community would decrease the risk that the virus had been silently transmitting, and had spread outside Auckland.

Health officials were tomorrow expecting results from ESR wastewater testing in Auckland and New Plymouth, which could similarly show whether or not there was widespread transmission.

Covid-19 modeller Professor Shaun Hendy said any new positive cases detected in the community wouldn’t necessarily be bad, if that helped establish a chain of transmission that had led to the family’s infection.

Contact tracers would then be able to follow that chain both backward and forward to find more close contacts and isolate any spread.

“But also, a weak positive test, and maybe some follow-up serology testing that perhaps shows someone had a historic infection, could be really helpful in establishing a link,” he said.

“Even if we can’t follow it all the way back to the border, it might give us a plausible path.

“So we need to see this as being slightly more nuanced than hoping for a whole bunch of negative tests.”

Otago University epidemiologist Professor Michael Baker added that timing mattered here.

The incubation period of the SARS-CoV-2 virus – that’s the time between exposure to the virus and symptom onset – is on average five to six days, but could sometimes be as long as 14 days.

Given the family’s positive test results had come through on Saturday, and the mother and daughter had been symptomatic for some time before that, Baker suspected there would have been enough time for any other connected cases to show up.

“If they were infected as part of a longer chain of transmission that is ongoing, you would be expecting to see other cases coming forward at this point,” he said.

“It could be an outbreak that’s not going anywhere – and has essentially been extinguished.”

What could be read into the fact that no close contacts had tested positive, even with the much more transmissible UK variant involved?

Baker said that, while it was true the B.1.1.7 variant could spread faster and more easily, the circumstances of the family’s infection had to be considered.

“It perhaps reflects how these individuals have responded to the infection, what their viral load was, but particularly, what patterns of contact they had when they were most infectious,” he said.

“Because there is a relatively narrow window people have when they are particularly infectious – and if an infected person isn’t out socialising much during it, in many cases they won’t infect anyone.”

Health experts have already pointed to the encouraging fact that none of the family members attended any potential “super spreader” events like large gatherings – while the daughter was only at school for five hours.

A link to the border

Baker thought it critical to continue focusing on the mother’s workplace, given some of her co-workers were sometimes air-side.

He said it was important to ask whether any of the co-workers had been ill at any point recently – and similarly crucial to carry out serology or anti-body testing which might reveal a historic infection among them.

“There’s been very little about this aspect of the investigation – how many staff in the mother’s workplace also work air-side? How many of them were originally tested, and what were the results?

“It could be that there’s a big hole there – and that they weren’t being regularly tested?”

Baker believed a border breach occurring outside the MIQ system remained the most plausible explanation.

“I think we’ve had people who infected staff working air-side, and they in turn infected other people outside that environment.”

Otago University epidemiologist Professor Nick Wilson said confirming a border breach directly linked to the family would be “pretty reassuring”.

“If we can’t find any signs of an infected border worker, then we might just be left with the idea that it came from a transit passenger or, under an extremely low probability, that it came from laundry associated with an infected person.”

ESR and Otago University virologist Dr Jemma Geoghegan said an open mind had to be kept to the possibility that the virus may have actually been picked up in the community.

She pointed to the fact the mother hadn’t been at work since February 5 – more than a week before the positive test result came through.

“Given she hadn’t been at work for some time, then it’s really hard to trace down that line of inquiry,” she said.

“We’ve just got to be aware that it might be a red herring, and be careful that we don’t close any doors to other areas.”

Bloomfield stressed officials were keeping an open mind about the source of the infection because the daughter developed symptoms before the mother.

“The important thing about a source is keeping an open mind and not to jump to conclusions, just because the mother works around the airport precinct is not to say ‘oh that’s where it’s come from’,” he said.

“One of the interesting things here is that the daughter reported onset of symptoms before the mother.

“So we have to be open-minded that she could be the first case, and could have got it somewhere else. And that’s what we’re trying to track down.”

A genetic match

One of the most worrying aspects of this scare – and a key reason why Auckland moved to lockdown – was that scientists hadn’t been able to find a genomic match to any cases detected in MIQ.

That suggested that the virus could have leaked out elsewhere in the border, or was part of a hidden chain of community transmission.

If a historic case was found among the mother’s co-workers through serology testing, that might suggest a strong explanation for the cases – but nonetheless wouldn’t give scientists the clear sample they needed to genetically link the two together to get a conclusive answer.

“The scenario in which we’d get a genetic match would be if we found more people in the community that had a link to the border,” Geoghegan said.

“That might be someone who had just left MIQ, or who was living with someone who’d just left MIQ.

“That’s the kind of scenario that we might actually quite link, because it means we know exactly how many people were probably in this chain of transmission, and we could find those answers we’re looking for.

“And we know, for instance, that we’ve had 10 or so leaks from MIQ in the past.

“Again, it’s about focusing a lot more broadly than just the workplace.”

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