Quarantined traveller who tested negative TWICE before leaving isolation infected six people and potentially 31 more with COVID-19 - as epidemiologist warns new cluster is a 'major concern'
Mystery surrounds how a man who tested negative for COVID-19 twice, later went on to infect six others.
A quarantined traveller who underwent managed isolation for 14 days in New Zealand's Christchurch, had no symptoms and did not return a positive reading.
But experts are now certain he has sparked a cluster of new infections after he left hotel quarantine.
At least 31 more people, who are close contacts of the confirmed cases, could also have contracted the virus.
New Zealand Prime Minister Jacinda Ardern speaks to the media on September 24 following reports a new coronavirus cluster has emerged
One theory is that the man may have had an unusually long incubation period.
'We are still not sure whether this is a case of a long incubation period, but that's a possibility,' Covid-19 modeller Shaun Hendy told RNZ.
'We have seen evidence of this overseas that there are some people who have a much longer incubation period.'
Another potential explanation is that 'something went wrong' at the isolation facility causing a breach in quarantine controls.
Genomic testing has confirmed all the six cases are part of the one cluster, but COVID-tracers are still not sure when the man became infected.
Mr Hendy said there should be some concern about the strange case, but added New Zealand health officials are confident all close contacts have been identified and that there are few undetected cases in the community.
One theory is that the man may have had an unusually long incubation period. (Pictured: a health worker carries out coronavirus testing in Auckland on April 2)
Two members of a family of three, who later tested positive, were on the same flight from Christchurch to Auckland as the infected man after leaving quarantine.
They later met another family member on a trip to Taupō and mingled with 18 others from various locations including the Bay of Plenty, Wellington, Christchurch and Hamilton.
Mr Hendy admitted the fact that the outbreak is not confined to one part of the country is a worry for contact tracers.
Epidemiologist Professor Sir David Skegg said the emerging cluster needs to be taken 'very seriously'.
'We shouldn't think that we've beaten this thing, we haven't. It's raging around the world and it's going to keep cropping up in New Zealand from time to time,' he said.
There are currently 65 active coronavirus cases in New Zealand with the vast majority of infections stemming from travellers in managed quarantine facilities.
On Wednesday, Auckland eased restrictions to COVID Alert Level Two after a second lockdown was ordered by Prime Minister Jacinda Ardern on August 31.
Aucklanders can now host and attend gatherings of up to 100 people.
Shoppers wearing face masks are pictured visiting a supermarket in Auckland on August 15