New Zealand officials are scrambling to halt a growing cluster of COVID-19 cases that has baffled health investigators trying to understand how the pandemic coronavirus regained a foothold on the island nation.
Officials on Tuesday announced four cases in one family in Auckland, the largest city in New Zealand. Before that, the country had gone 102 days without any local transmission. Throughout the pandemic, New Zealand has been among the most successful countries in the world at responding to and holding back the pandemic coronavirus, relying on swift and thorough testing and tracing as well as rigorous social distancing and lockdown orders.
But the new cluster has stumped investigators, who are now exploring all the possible ways the coronavirus may have slipped back in—including that it arrived on the packaging of frozen-food shipments and infected a worker unpacking them.
Meanwhile, the cluster has grown to at least 17 as of Thursday. Auckland has been wrenched back into lockdown measures, and officials have raised the alert level for the rest of country, reinstating some restrictions.
Cold Case
The first person in the cluster to test positive was a woman in her 50s who had been symptomatic for five days. Of the woman’s six family contacts, three also tested positive Tuesday: a baby boy, a woman in her 20s, and her husband, who is thought to be the first to become infected and developed symptoms approximately July 31, according to the The New Zealand Herald. One of the family members works at the lending company Finance Now, and the man works at a facility operated by Americold, an Atlanta, Georgia-based company that transports and stores goods at controlled temperatures. Americold operates in the United States, Canada, Australia, and Argentina, as well as New Zealand.
The infected Americold employee’s job involved handling frozen foods destined for grocery stores and food service companies. He had been on sick leave for nine days at the time that he tested positive, according to Americold NZ Managing Director Richard Winnall, who spoke to the Herald.
Winnall stressed that the chance of the virus spreading to consumers from frozen foods the infected employee handled appeared “improbable.” He noted that the frozen-food shipments come in several layers of packaging, and the infected employee likely did not touch the packaging layers that are eventually touched by consumers or food service employees. Winnall also noted that the infected employee would have been wearing personal protective gear, including gloves, decreasing the likelihood that he transferred infectious virus onto the food packages.
“Looking at all the options”
Still, without a clear explanation of how the employee and his family were infected in the first place, health investigators are exploring the possibility that he was infected by virus particles shipped on the frozen goods. Health officials and experts suggest that this seems unlikely but not impossible. There have been several reports from China of health officials detecting genetic material of the coronavirus, SARS-CoV-2, on frozen goods. In an example this week, authorities in the eastern Chinese port city of Yantai detected traces of the virus on imported frozen seafood. The genetic traces suggest contamination with the coronavirus but not necessarily whole infectious virus particles.
New Zealand’s Director-General of Health Ashley Bloomfield said this week that surfaces at the Americold facility will be tested to see if frozen freight or something else may have been the source of the new infections. “We do know from studies overseas that, actually, the virus can survive in some refrigerated environments for quite some time,” he said. For the investigation, “we start by looking at all the options and ruling them out, and that's the position we’re in at the moment.”
Unlikely, but not impossible
The possibility that SARS-CoV-2 could survive on shipments of frozen goods isn’t wild. Studies have suggested that some virus particles can remain infectious for three days on plastic surfaces at room temperature. And the virus is more stable at lower temperatures, like those in a refrigerated warehouse.
This means that the virus could remain viable for even longer, infectious disease and food safety researcher Hamada Aboubakr tells Ars. Aboubakr is a researcher at the University of Minnesota and was recently the first author of a scientific review on the stability of SARS-CoV-2 on surfaces in different conditions.
Aboubakr suggests it’s theoretically possible that SARS-CoV-2 could spread through contaminated food or food packaging. In addition to the cold survival, there is early laboratory data suggesting that the virus can survive highly acidic conditions, similar to the environment of the human stomach. But he notes that experts are skeptical of this. Overall, he says, “there is no sharp answer” to the risk of food and food packaging because no studies have confirmed such as link.
The point is echoed by the World Health Organization, which notes that there is “currently no evidence that people can catch COVID-19 from food or food packaging.”
Aboubakr says that investigators in New Zealand will need a lot more data and information to assess the risk of spread from freight and pin the new cases to contaminated packages.
Bad luck
Infectious-disease researcher Amandine Gamble agrees. Gamble is a researcher at the University of California, Los Angeles, who recently led a study on treatments to inactivate SARS-CoV-2. “It is very plausible that SARS-CoV-2 can remain viable on frozen surfaces for several days,” she tells Ars. “However, it is not clear whether the virus can easily be transmitted via contaminated surfaces.”
There are many unknowns about the situation and basic transmission of SARS-CoV-2, she adds. For instance, we don’t know how many viral particles is enough to trigger an infection. But, she says, walking through the scenario in which a worker would be infected through a contaminated package, “it may seem an unlikely route of transmission.”
In such a scenario, let’s imagine an infected person coughs on a frozen bag, excreting X number of viral particles onto the bag, she says. Several people might then handle the bag, and the bag is likely in contact with other bags and containers, all leading to some of the particles getting rubbed off. Then during shipping, some virus is naturally degraded—even if it’s a slower rate than would be seen in warmer temperatures. Then a worker touches the bag, transferring some virus particles from the bag to their hands. The worker touches their face, transferring yet fewer particles from their hands to their face, then inhales just some of those particles. And only some of those will even encounter susceptible cells. In the end, the worker would encounter a much, much smaller number of virus particles than the initial X quantity on the bag.
Being “purely speculative,” such a transmission might be possible, Gamble says, if there was a very large number of virus particles on a bag to begin with—through a large, direct sneeze or contamination from several infected people—and the bag shipped quickly, didn’t have much handling, and a receiving worker had no protective equipment and quickly touched their nose. “It is unlikely that all these events aligned—although not impossible,” she says. “But it would be very bad luck.”
As for consumers, Gamble suggests that if frozen foods were an important risk, it’s unlikely New Zealand would have been able to go more than 100 days without seeing other cases. For anyone worried about getting SARS-CoV-2 from frozen foods, she recommends making sure to frequently wash hands and common surfaces.
Cluster continues
While the source of the cluster remains unknown, health officials have announced 13 additional cases Thursday. All of those cases are linked in some way to the original four, including three other Americold employees and seven of their family members. An employee at Finance Now and a family member of that employee also tested positive. Last, there was one community case linked to the cluster.
One of the new cases is a student at a local grammar school, and another had recently visited an elderly care home. Officials are racing to identify, test, and quarantine the mushrooming number of contacts.
According to a new report by the Herald, genetic testing suggests that the new cluster of cases is not linked to earlier cases isolated in quarantine facilities. Deputy Prime Minister Winston Peters has suggested that the cluster may be the result of a breach of the country’s quarantine system, but a spokesperson for the prime minister’s office said there was no evidence of such a breach.
8/14/2020: This story has been updated to correct misreported information about the original four cases in the cluster.
reader comments
315