Beijing: Studies into clusters of Covid-19 cases show that contaminated cold-chain food products are the major cause of the outbreaks, highlighting the need for protection of workers within the industry, experts said.
“Research has indicated that the virus can survive on cold-chain food and packaging during long distance shipping and may cause human infection, in particular to high-risk people such as dockworkers, ” said Liu Zhaoping, a researcher at the China National Centre for Food Safety Risk Assessment.
“But the likelihood of food-to-human transmission is lower than other routes of transmission.”
Investigations into the source of the outbreaks in cities across China, including Beijing and the port cities of Dalian, Liaoning province, and Qingdao, Shandong province, found many of them could be traced to workers at cold storage areas, seafood processing plants and markets selling imported frozen food products, he said.
In many areas, the RNA of the Covid-19 virus was detected on the surface of frozen food such as salmon, shrimp, beef and chicken, as well as their packaging.
Most of them were imported from countries where the pandemic is still wreaking havoc, Liu said.
Meat and poultry processing facilities are more prone to outbreaks due to the cold and humid environment, where it is easier for workers to catch and transmit respiratory diseases.
Food products and their packaging are likely to be contaminated by droplets exhaled from virus carriers.
Studies have shown that the virus remains highly stable under freezing conditions, so it may survive cold-chain transportation.
“There is growing knowledge to suggest that the novel coronavirus could have a longer survival time at lower temperatures, ” said Christopher Elliott, professor of food safety at Queen’s University in the United Kingdom.
Covid-19 outbreaks in port cities such as Dalian and Tianjin were caused by harbour workers who were infected after coming into contact with frozen food and packaging, he said.
“The isolation of a live virus in the Qingdao case study has confirmed the transmissibility from food packaging to humans, ” he said.
The investigation into the Covid-19 outbreak in Qingdao for the first time isolated live samples of novel coronavirus taken from imported frozen seafood packaging, proving the possibility of virus transmission via frozen food, according to a study published by the Chinese Centre for Disease Control and Prevention in October.
The possibility of the virus being transmitted via frozen food was first raised after a Covid-19 outbreak at a wholesale market in Beijing in June.
Cutting boards used to handle imported salmon in the market tested positive for the virus.
Before the outbreak, Beijing had reported no new domestically transmitted cases for about two months, and the virus was effectively under control in the rest of the country. — China Daily/ANN