Scientists are seriously investigating the possibility that refrigerated and frozen meat could be contaminated with the coronavirus that causes covid-19. Officials in New Zealand and China have even speculated that imported frozen foods could be behind recent local cases, but, for now, there’s no good evidence that anyone has been infected from handling food.
On Tuesday, health officials in New Zealand ruled out that frozen foods sparked a recent resurgence of covid-19 cases there. A new study released this week, however, found that the coronavirus can survive and remain infectious on the surface of refrigerated and frozen meat for at least 21 days. Even so, just because the virus can survive in certain circumstances doesn’t mean that it’s necessarily transmitted that way.
The novel coronavirus, called SARS-CoV-2, is primarily spread through infectious droplets and/or aerosols that are emitted from an infected person’s mouth and nose and are then breathed in by another person. But early on in the pandemic, fomite exposure (touching a recently contaminated surface then your mouth, eyes, or nose) was also thought to be an important route of transmission. Nowadays, however, the risk of catching covid-19 through fomites is considered relatively low, compared to close contact with infected people. The World Health Organisation has specifically said that there’s no evidence of food having been a source of infection during the pandemic, either through eating or touching contaminated food.
At the same time, however, health officials in China have reported finding traces of the virus on frozen food packages, and they’ve theorised that frozen imported food from Europe may have been the initial spark of transmission that led to new cases in Beijing emerging recently, nearly two months after the last documented outbreak in the city. Countries such as Vietnam and New Zealand have also experienced small new clusters of covid-19 as of late, after even longer periods of no reported local transmission, raising the question of how they started.
The case for frozen food being a conduit of covid-19 spread is entirely circumstantial at this point, and it’s very possible that all these recent outbreaks were caused by breaches in the strict restrictions and isolation measures for travellers enacted by countries like New Zealand. In China, for example, officials might be politically motivated to blame outside parties, like meat imported from Europe, for their recent outbreaks. But this new study, released on the preprint website biorxiv, seems to show that it’s at least theoretically possible.
Researchers in Singapore and Ireland conducted a relatively simple experiment in the lab. They added viable, infectious levels of the virus to frozen pieces of salmon, chicken, and pork taken from a local supermarket in Singapore. Then they stored the meat in a fridge or freezer, periodically taking samples to test for infectious virus for the next 21 days. The meat was stored at temperatures of 4 degrees Celsius, -20 degrees Celsius, and -80 degrees Celsius.
Across all of the conditions, the researchers found, levels of the virus stayed roughly the same throughout the study period. They concluded that the virus remained capable of infecting people in both the refrigerated and frozen food during that time as well, if a person were to handle the meat and then touch their mouth or nose. (No case of covid-19 has been linked to consuming contaminated food.)
“Our laboratory work has shown that SARS-CoV-2 can survive the time and temperatures associated with transportation and storage conditions associated with international food trade,” they wrote.
Preprint research like this hasn’t gone through the traditional peer-review process. That doesn’t mean that the findings aren’t accurate (nor does something being peer-reviewed mean it’s definitely correct), but it does warrant some cautious scepticism for now. And as even the authors acknowledge, the results don’t suggest that lots of people are getting covid-19 from touching frozen food.
But even a rare transmission event could spell trouble for containing the virus, if the potential for it happens often enough. We know already that food processing factories have been hotspots for covid-19 outbreaks, in part because of their working conditions and because many of the people employed there live in communities where exposure to the virus is more common already. So the potential for food workers to become infected and then contaminate food products is certainly there. Because food is shipped internationally, the possibility of contaminated food reaching people in more isolated countries is also real.
“The international food market is massive and even a very unlikely event could be expected to occur from time to time,” the authors note.
This theoretical transmission risk of covid-19 needs to be further studied before we can be sure it exists. If it does, though, it highlights the need to keep vulnerable food workers as safe as possible from the virus. For consumers, the authors wrote, the same precautions that we should already be taking might apply even more now: Wash your hands after touching uncooked food and throughly cook everything you eat.