The research, which has not been peer reviewed, called ‘Seeding of outbreaks of COVID-19 by contaminated fresh and frozen food’ concluded that it was possible for contaminated imported food to transfer virus to workers as well as the environment. It has been published on BioRxiv, the preprint server for biology (Researchers: Dale Fisher, Alan Reilly, Adrian Kang Eng Zheng, Alex R Cook, Danielle E. Anderson (https://doi.org/10.1101/2020.08.17.255166).
The study stated: "While it can be confidently argued that transmission via contaminated food is not a major infection route, the potential for movement of contaminated items to a region with no COVID-19 and initiate an outbreak is an important hypothesis.
"It is necessary to understand the risk of an item becoming contaminated and remaining so at the time of export, and of the virus surviving the transport and storage conditions."
Infection remained in all samples
The researchers took individual pieces of salmon, chicken and pork sourced from supermarkets in Singapore that were sliced into cubes and added 200 μl of 3 × 106) TCID50/ml SARS-CoV-2 to each cube. Infection was found to remain for three weeks in the refrigerated (4°C) and frozen (–20°C and –80°C) samples.
The study concluded: "Contamination of food is possible, and virus survival during transport and storage is likely.
"We believe it is possible that contaminated imported food can transfer virus to workers as well as the environment. An infected food handler has the potential to become an index case of a new outbreak. The international food market is massive and even a very unlikely event could be expected to occur from time to time.
The scientists claimed that this might provide an explanation for the re-emergence of COVID-19 outbreaks in regions with apparent local eradication such as New Zealand.
The Beijing Xinfadi wholesale food market outbreak led to concerns that imported contaminated food could seed new clusters.
The research also said that a well-recognised feature of the COVID-19 pandemic was the number of clusters within meat and seafood processing facilities.
The UK Food Standards Agency has consistently said that the probability of receiving potentially infectious exposures via consumption or handling of food was “negligible”.
Richard Harrow the chief executive of the British Frozen Food Federation (BFFF) said: “BFFF is aware of reports circulating in the media regarding New Zealand investigating freight as the possible transmission route for a recent COVID-19 outbreak. We are monitoring the situation closely and as always, we will be led by the scientific evidence as and when it is published.
“According to the World Health Organisation, there are currently no confirmed cases of coronavirus being transmitted through food or packaging.
“Latest UK research from the Food Standards Agency has shown that the probability that UK consumers will receive potentially infectious exposures of SARS-CoV-2 via the consumption of food is ‘Negligible’ or [via] the handling of food contact materials or packaging is “Very Low.”
Who conducted the research?
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- National University Health System, Singapore
- Division of Infectious Diseases, National University Hospital, Singapore
- Centre for Food Safety, University College Dublin, Ireland
- Programme in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore
- Saw Swee Hock School of Public Health, National University of Singapore