Cold chain products are the main cause of infections, according to studies

Disease prevention and control workers collect samples of frozen products in Tianjin's Nankai District on November 9, 2020.

Studies on clusters of COVID-19 cases in recent months show that contaminated cold chain food products are the leading cause of outbreaks, highlighting the need for protection of workers associated with the industry, they said. The experts.

“Research has indicated that the novel coronavirus can survive in cold chain food and food packaging during long-distance shipping and can cause human infection, particularly to high-risk individuals such as port workers,” said Liu Zhaoping, researcher at the China National Center for Risk Assessment for Food Safety.

"However, the probability of transmission from food to humans is considered lower than with other routes of transmission."

Investigations into the origin of the outbreaks in Chinese cities, including Beijing and the port cities of Dalian, Liaoning Province, and Qingdao, Shandong Province, found that many of them could be traced to workers in cold storage areas, plants seafood processing and sales markets. imported frozen food products, he said.

In many areas, RNA from the new coronavirus has been detected on the surface of frozen foods, including salmon, shrimp, beef, and chicken, as well as on their packaging. Most of them were imported from countries where the pandemic is still raging, 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 contract and transmit respiratory diseases. Food products and their packaging are likely to be contaminated by droplets exhaled by virus carriers through actions such as breathing, coughing, and talking.

Studies have shown that the new coronavirus is very stable in freezing conditions, so it can survive cold chain transport.

Christopher Elliott, professor of food safety at Queen's University in the UK, said: "There was growing knowledge to suggest that the novel coronavirus could have a longer survival time at lower temperatures."

The COVID-19 outbreaks in port cities such as Dalian and Tianjin were caused by dock workers, who became infected after coming into contact with frozen food and packaging, he said.

“The isolation of a live virus in the Qingdao case study has further confirmed the transmissibility of food packaging to humans,” he said.

Research into the COVID-19 outbreak in Qingdao isolated live samples of the new coronavirus taken from imported frozen seafood containers for the first time, demonstrating the possibility of transmission of the virus through frozen food, according to a study published by the Center. Chinese for Disease Control Prevention in October.

The possibility of the virus being transmitted through 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 on the market tested positive for the virus.

Before the outbreak, Beijing had reported no new cases of domestic transmission for about two months, and the virus was effectively under control in the rest of the country.

A research article published jointly in October by Tsinghua University, the Beijing Center for Disease Control and Prevention, and the Chinese Academy of Medical Sciences and other institutes said the outbreak was most likely caused by imported contaminated frozen food. .

During an outbreak in Dalian between December 15 and January 11, involving 51 confirmed COVID-19 patients and 32 asymptomatic carriers, epidemiologists identified imported frozen foods as the source of the outbreak.

Five longshoremen were infected in early December while unloading frozen food from a foreign cargo ship. They later spread the disease through person-to-person transmission, according to the Dalian government.

Recent studies have also found that shipping containers can also harbor live coronavirus in cold winter temperatures.

In November, Shanghai health authorities said that two non-mask workers became infected while cleaning a sealed container arriving from North America.

All of China's major clusters of infections since December were caused by incoming travelers or contaminated goods from the cold chain, Health Minister Ma Xiaowei said last month.

Intensified supervision

China has stepped up monitoring of imported frozen foods since the June outbreak in Beijing, to cover the cold food chain industry across the country. Strict epidemic prevention and control measures have been applied in the sector, and frontline dockworkers have been included in the list of priority occupations for COVID-19 vaccination.

Liu from the Food Safety Center said that as COVID-19 continues to spread around the world, relevant departments should strengthen inspection of incoming cold chain products, especially from countries or regions with severe outbreaks.

Meanwhile, measures to protect cold chain workers should be increased to minimize the risk of infection, he said. “Keeping all workers in the food supply chain healthy and safe is vital to their personal well-being, to their families, and to ensuring that consumer needs are met.”

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