Questions raised after source of New Zealand’s COVID-19 outbreak traced to a cold storage facility
Vendors wait for customers at their stall selling frozen meat and seafood balls at a market in Beijing on June 20, 2020. (NICOLAS ASFOURI / AFP)
Can the COVID-19 virus be carried on the packaging of refrigerated food?
It is a question scientists around the world are debating as more cases appear to come from frozen food packaging such as cardboard and plastic. While the incidence is low, it nevertheless poses serious questions for global supply chains.
And despite the very limited likelihood of catching COVID-19 from packaged refrigerated food, an element of risk remains, scientists say.
The recent outbreak in New Zealand, which had been COVID-free for 102 days until fresh cases were recorded on Aug 11, came as a complete surprise to the nation of 5 million. The locally acquired cases of coronavirus were confirmed in New Zealand’s biggest city, Auckland, which prompted the government to introduce strict level three lockdown measures on Aug 12.
The rest of the country was put into level two lockdown, with both lockdown periods extended until at least Aug 26 as further cases of coronavirus were confirmed.
Prime Minister Jacinda Ardern also announced she was delaying the country’s parliamentary election by four weeks to October 17.
On Aug 19, the country recorded five new cases in the community, and one in managed isolation facilities, prompting Ardern to say the drop indicated New Zealand was not seeing a surge of COVID-19 in the community. There were 13 cases reported on Aug 18.
“The roll out of our resurgence plan is working as we intended,” Ardern said, adding there was no intention to raise the level of restrictions in Auckland.
The source of the outbreak was traced to a cold storage facility which handled imported frozen foods.
Studying source
It was first thought the virus had been brought in on the packaging of frozen food — a theory now under investigation in China, which has had similar cases in recent weeks.
On Aug 18, New Zealand’s health department said the virus did not originate from frozen food shipments.
“It seems clear now that the possibility is being ruled out from that investigation,” said Director-General of Health Ashley Bloomfield, according to Reuters, without supplying details of the investigation.
Officials in Shenzhen, Guangdong province, recently found traces of the virus on chicken wing shipments imported from Brazil.
On Aug 16, authorities in Guangzhou, the provincial capital, suspended imports of frozen meat and seafood from global COVID-19 hotspots such as Brazil over concerns of virus transmission.
Dr Sacha Stelzer-Braid, a virologist in Australia at the University of New South Wales, said the COVID-19 virus can remain infectious at low temperatures. “We store the virus in freezers,” she told China Daily.
“While the virus can survive in low temperatures, its infectivity will diminish over time,” she said.
However, she doubts that refrigeration is a primary source for infection.
“The evidence we have so far is that the virus is transmitted via droplets in the air, not on the wrapping of food products.
“If you work in cold storage and have the virus, you are excreting it as you cough or sneeze. The droplets while airborne will eventually land on the coating, such as plastic.”
She said the coating will remain infectious during transport. When the products arrive, they are unpacked, but the probability of getting the virus is “very low”, she said.
Complex issue
Associate Professor Tim Newsome, a virologist at the University of Sydney, said there are “no simple answers, as transmission is a complex chain of events”.
What we do know is that the virus can survive better at low temperatures than at room temperature, he told China Daily.
“You still need to consider other factors such as humidity and temperature to get closer to the truth. Dried virus behaves differently to virus in solution, for example.
“How long it can last on packaging in the real world will depend on all of these parameters,” Newsome said.
“Another question that needs more work is how do you get the virus from packaging to causing disease in your lungs, and what quantities are needed. We know the virus is mostly transmitted via sustained and close contact, so current advice on face masks and social distancing should be followed.”
Donald Schaffner, a professor and director of Rutgers’ food science graduate program in the United States, said the virus can survive for long periods of time under frozen conditions. “The primary risk is with the packaging,” Schaffner told NJ Advance Media on July 31.
Associate Professor Rowland Cobbold from the University of Queensland, an expert in zoonotic diseases, as well as food safety in meat and microbiology, said: “Like many viruses, COVID-19 survives better in colder temperatures.”
But how long it can survive depends on the specific environmental conditions, he told China Daily.
Can it survive on wrappings such as cardboard and plastic? Cobbold said the answer is yes, but added: “How this might relate to infectivity is not clear.”
“There are a few publications that have examined COVID-19’s survival under different environmental conditions and on various surfaces.”
He said from these papers, the virus can survive anywhere from a few hours to a few days, with better survival on “less-porous materials such as plastic and stainless steel, as compared to cardboard.
“There needs to be sufficient numbers of viable viral particles present on the surface to constitute an infectious dose,” Cobbold said.
