Returnees who spent their managed isolation in the Pullman Hotel and were recently released are being urged to self-isolate and get tested "immediately".
Covid-19 Response Minister Chris Hipkins today released more details about the latest community case, a 56-year-old woman who lives south of Whangarei.
The woman arrived back in New Zealand from Europe on December 30 and spent 14 days at the Pullman after getting negative tests on January 2 and 10.
She left the Pullman on January 13 and was tested again on Friday January 22.
Between leaving the Pullman and Covid being confirmed on Saturday, she visited 28 places around Northland and anyone there at the same time has been asked to get a test and to self-isolate until the results are known.
The woman's husband has tested negative, Hipkins said earlier today, as had another close contact - her hairdresser.
Hipkins urged travellers who stayed in MIQ at the Pullman Hotel from January 9-24 asked to self-isolate "immediately".
He said genome sequencing had confirmed the strain was the more infectious South African strain.
Further investigations had also revealed the strain was a direct match and likely from a person who went into MIQ on January 9.
CCTV footage is being examined for any interaction but Hipkins confirmed the woman and the person with Covid were on the same floor in "close proximity".
"The source of infection is likely to be a fellow returnee during the person's stay at the Pullman Hotel.
"The two people occupied rooms in close proximity to each other on the same floor of the Pullman Hotel and I have been advised by officials that the source of infection was a direct one.
"We don't know exactly how the infection took place at this point."
Hipkins said the leading theory was cross-contamination in isolation.
He said there was currently no evidence of the returnees mingling at any point.
"This person appears to have done everything right and maintaining distances and wearing a mask."
Hipkins said given the latest case, the decision had been made to delay the release of the 46 people that were due to leave the Pullman today.
As for testing of staff, of approximately 220 people, 114 had been tested so far this week, he said.
The remainder of tests will be completed by 4pm.
Dr Ashley Bloomfield said the woman reported chills but not a runny nose or a cough.
"Some people are infected and don't display any symptoms at all."
Bloomfield said contact tracing on the case has identified 15 people as close contacts
Thirteen of them worked in retail stores and it is not immediately clear who served the case, he said.
"All have been contacted."