Coronavirus Covid-19: 'False-negative' test threat prompts need for border beef-up - experts

Health experts are warning "false-negative" Covid-19 test results continue to threaten New Zealand - and have renewed calls for an urgent border review.

In an editorial published in the New Zealand Medical Journal today, a group of Otago University researchers suggest our border system should take a risk-based approach, imposing tougher requirements for travellers from mass-infected countries.

The researchers said while recent outbreaks have been swiftly controlled by well co-ordinated public health responses, every case of the virus slipping into our community was an "extremely high-risk event".

They singled out the danger posed by false-negative tests, where someone with Covid-19 could return a negative result, leaving them unaware they could be spreading the virus.

And there were indications our border system may be seeing many such false-negative results, the researchers said.

In New Zealand's first wave, just 19 per cent of those cases that were genomically sequenced led to further infections.

That suggested the number of true introductions was likely much larger than the number of observed outbreaks.

But the researchers argued weaknesses around testing shouldn't be seen as flaws involving single cases - but our whole border system.

They set out a range of ways New Zealand could prevent false-negative cases from starting community outbreaks.

One was moving to a "traffic light" system where travellers coming from "red zone" places with high levels of transmission would be required to take tests and spend time in quarantine before flying here.

They said measures taken by airlines to stop spread on flights should be reviewed, as should testing regimes and how risk of infection in managed isolation and quarantine (MIQ) facilities were managed.

Those facilities could even be moved outside cities to a re-purposed centre, such as at Air Base Ohakea, and airports could consider using Covid-19 detection dogs.

Border workers could be equipped with personal protective equipment and contact tracing tech, have their own testing schedules timed to their work shifts and even be screened where possible with wastewater sampling.

"A high standard of strategic risk management is required because impacts on population wellbeing from breaches in control of this highly transmissible infection are substantial, and should never be underestimated."

This week, one of the new paper's authors, Professor Michael Baker, told TVNZ's Breakfast programme the current danger to New Zealand may be the "highest it's ever been".

While Kiwis were preparing to take their summer breaks, the virus was raging overseas.

There were currently 74.1m cases worldwide, and travellers from many of the worst-hit countries would continue arriving at New Zealand's borders over coming months.

Health Minister Chris Hipkins last month ordered a raft of border improvements, and has just released the Government's plans to deal with a "worst case scenario" outbreak over summer.

Meanwhile, another study published today has shown how unplanned admissions to Wellington's main intensive care unit (ICU) dropped off dramatically over lockdown.

The paper, led by Wellington Hospital ICU co-clinical leader Dr Paul Young, raised the concerning possibility that patients with potentially life-threatening diseases may have avoided hospital.

The study looked at unplanned ICU admissions over the first 35 weeks of the year and compared them with the five previous years, to find rates fell by just over a third.

The analysis found admissions for heart, gastrointestinal, sepsis and trauma cases were lower than any of the preceding five years - and that the drop-off started when New Zealand moved to alert level 4.

"One potential concern with the lockdown is that patients with potentially life-threatening diseases may not have presented to hospital," they said.

While their data couldn't rule that out, they added that trends across case types were still broadly similar to past years.

The authors said their findings generally aligned with other studies - including one that reported a 43 per cent drop in injuries turning up at one trauma centre over lockdown.

It also raised implications for dealing with future outbreaks.

If the same rates were seen at other ICUs, they noted, it meant capacity freed up as a result of lockdown was actually far greater than that which came from cancelling elective surgeries.