Auckland could have as many as 24 coronavirus cases, some which still have to be detected, a leading scientist said.
Professor Shaun Hendy, who leads the research group Te Pūnaha Matatini, says computer modelling work began soon after it emerged the Auckland family had contracted COVID-19 from an unknown source.
“The fact that we’ve found it first in a family where there’s no immediate, obvious connection to the border tells us that actually the epidemic is probably larger than it would be if we’d found it in someone who was working at the border.
“The later you detect it, the larger the epidemic you’re potentially looking at.”
The source of the outbreak has baffled health officials, who said they were confident there were no local transmissions of the virus for 102 days and that the family had not travelled overseas.
“We are working hard to put together pieces of the puzzle on how this family got infected,” said Director General of Health Ashley Bloomfield.
Investigations were focussing on the potential the virus was imported by freight. Bloomfield said surface testing was underway in an Auckland cool store where a man from the infected family worked. News website Stuff named the company as Americold, in Mount Wellington.
“We are very confident we didn’t have any community transmission for a very long period,” Bloomfield said during a televised media conference. “We know the virus can survive within refrigerated environments for quite some time.”
The cool storage facility has been closed down along with three other sites the company had around the city, he said. The 160 staff across all the facilities would be tested for COVID-19.
China has reported instances of the coronavirus being detected on the packaging of imported frozen seafood.
In July China claimed that it had detected the virus in the outer packaging of frozen shrimp from Ecuador, as well as the container walls housing the seafood. However, subsequent tests cleared the food itself of carrying the virus.
The World Health Organisation website states there is currently no confirmed case of COVID-19 transmitted through food or food packaging. However, it also notes that studies have shown that the virus can survive for up to 72 hours on plastic.
Prime Minister Jacinda Ardern said the surfaces would be tested because, “while we primarily look for human-to-human transmission” they needed to be sure freight wasn’t involved.
Professor Michael Baker, an epidemiologist, said it was an “intriguing idea” that the virus might survive on a surface across the border.
He was unaware of this being documented in research.
“In general the role of surfaces for transmitting the virus has probably been over emphasised in the past,” he said.
“There’s much more focus now on transmission in indoor environments, and respiratory droplets and aerosols.”
It was poorly ventilated, indoor environments where people incubating the illness came into contact with others that posed the greatest risk, he said.
The first of four cases identified on Tuesday evening was a person in their 50s living in south Auckland. This person worked at a finance company with 130 others, and three people working there were now symptomatic.
The second case, the partner of the first case, was the cool storage worker. A third case, a woman in her 20s, travelled to Rotorua on Saturday with four others on the weekend of August 9.
The fourth case was a pre-schooler who also travelled to Rotorua.
Residents of Auckland, home to around 1.7 million people, returned to level 3 restrictions at midday on Wednesday, requiring people to stay at home unless for essential trips.
The rest of the country was placed back into slightly looser level 2 restrictions. The restrictions will initially remain in place until Friday.
“I have huge sympathy … this is unsettling,” Ardern said. “Stay kind, look after one another.”
Police set up roadblocks around the city and supermarkets began rationing the sale of some staple products amid a rush to the shelves. Access to aged care nursing homes was restricted to staff and essential deliveries.
Bloomfield said three people at the finance company were showing symptoms of the virus. The business has been closed, with testing underway on other workers.
Health officials were prepared to test tens of thousands of people in the coming days, Bloomfield said.
Ardern also delayed a key step towards the September 19 general election, suspending the dissolution of Parliament until Monday. No decision had yet been made on delaying the actual poll, she added, noting there was a window to defer until November 21.
The major opposition party called for the election to be delayed until November as it cancelled its campaign launch scheduled for the weekend.