Authorities in the eastern Chinese port city of Yantai said the new coronavirus was detected on packaging of imported frozen seafood.
The confirmation on Tuesday comes as administrations around the country step up monitoring of frozen food processing in response to outbreaks linked to the industry in the capital Beijing and the northeastern city of Dalian in Liaoning province.
The most recent contamination was detected at the Yantai Economic and Technological Development Zone in Shandong province on Sunday during blanket tests on frozen food and processing workers, the official Dazhong Daily reported.
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The test results were reconfirmed by the city’s centre for disease control and prevention on Monday, the report added, citing Yantai’s Covid-19 steering group.
None of the people who had close contact with the seafood batch tested positive but they have been placed under quarantine, the report said.
Yantai officials said the affected seafood came in one batch from a foreign vessel that entered the country via Dalian port.
The officials did not specify what kind of seafood was involved or where it came from, saying only that a “small quantity” of the seafood had been reprocessed and exported, while the remainder was still in cold storage and had not entered the domestic market.
Dalian health officials said earlier this month that the Covid-19 outbreak in the city in July centred on a cluster linked to a chilled seafood processing firm, with a high degree of similarity in the coronavirus strain found in the patients.
Sixty workers and managers, accounting for about two-thirds of the processing firm’s staff, were infected by the novel coronavirus and in turn transmitted it to other people outside Liaoning.
Wu Zunyou, chief epidemiologist of the Chinese Centre for Disease Control and Prevention, said on state television late last month that the outbreaks in Dalian, Beijing and even the initial epicentre of the pandemic in Wuhan “shared certain similarities” and were all related to seafood processing or sales.
He said researchers had simulated the spread of the virus using fluorescent powder at Beijing’s Xinfadi market, where the capital’s outbreak emerged in June, and found once the environment was contaminated, people could be infected through aerosols and then infect others through human-to-human transmission.
“These markets have common environments that are damp and have relatively low temperatures, which are suitable for the virus to survive,” Wu told state television.
The CDC also issued a guideline on July 30 about strengthening Covid-19 monitoring in regional wholesale wet markets, stressing the need for surveillance of chilled and frozen meat and seafood stalls, as well as markets with closed and damp areas.
The guideline specified a wide range of sites and equipment for testing, including tools, sewage systems, freezers and food. Workers in these markets should also have swab tests as well as having their clothes and hands tested.
But the US CDC says the risk of getting Covid-19 from food packaging “is thought to be very low”, according to its website.
Professor Jin Dong-yan, a molecular virologist at the University of Hong Kong, said the public should stay vigilant although no Covid-19 cases in Hong Kong and mainland China had yet been caused by touching food or food packaging. He suggested people cook meals thoroughly and avoid eating high-risk food such as sushi.
He added that the chances of being infected by the virus on packaging would be low if the frozen food was shipped in over a long distance.
“After long-distance shipping, the activity of the virus will just go down and will not go up,” Jin said. “Shrimp and fish cannot support the growth of the virus. The virus cannot grow, replicate or multiply in those foods or packages, it will just stay there and die out.”
Yet the virus could still be detected because of the high sensitivity of the nucleic acid detection methods, according to Jin.
China found traces of the novel coronavirus on packaging and the inner wall of a container of frozen shrimp imported from Ecuador in early July, but the shrimp were not contaminated with the virus.
Andrea Britton, convenor of the Public Health Association of Australia’s One Health Special Interest Group, said that while coronaviruses could remain stable at low and sub-zero temperatures for a certain period, the Sars-CoV-2 coronavirus was susceptible to common cleaning and disinfection methods.
People should wipe down packaging of frozen food and regularly used food areas with suitable disinfectant and wash their hands properly, she said.
The Yantai government cautioned all imported food processing firms to strictly implement preventive and control measures against Covid-19.
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