China has linked seven COVID-19 outbreaks and almost 700 cases to contaminated imported frozen food packaging materials.
Scientists said the work supports speculation that cold-chain foods act as a pathway for SARS-CoV-2 and might present a risk for virus transmission between countries and regions.
They added handlers and processors of imported frozen foods should be effectively protected, monitored daily for symptoms of COVID-19, and tested for SARS-CoV-2 nucleic acid at regular intervals.
Seven outbreaks and 689 cases were linked to imported cold-chain foods from June 2020 to mid-July 2021, according to the study in China CDC Weekly.
Sampling findings
Investigations of an outbreak at Xinfadi Market in Beijing June 2020 found five samples from salmon in the original sealed package in the company’s cold storage were positive for SARS-CoV-2.
An outbreak in Dalian, in July 2020, was associated with imported cold-chain foods. The porter was infected through contact with the outer packaging of frozen cod contaminated with SARS-CoV-2. Active and infectious viruses were not isolated from the samples of food in Beijing and Dalian.
Two infected dock workers who transported imported frozen cod for 10 hours in two separate storage warehouses on the same freighter in Qingdao, were reported to be infected with the virus. An active SARS-CoV-2 sample was isolated from a contaminated outer packaging sample of the frozen cod.
The first infected cases of two outbreaks in Tianjin Municipality in November 2020 were porters who were in close contact with contaminated outer packaging of imported frozen food, or exposed to the virus-contaminated environment during handling of frozen foods.
The virus sequence that led to the Yingkou City, Liaoning Province, and Liuan City, Anhui Province, COVID-19 outbreaks in May 2021 was linked to the Dalian COVID-19 outbreak in July 2020.
SARS-CoV-2 contaminated frozen cod were kept in cold storage for 11 months in Dalian since July 2020, but still infected workers during handling. Researchers said this shows SARS-CoV-2 can maintain its infectivity for at least 11 months at a low temperature of minus 18 degrees C (minus 0.4 F).
The study supports speculation that the infected COVID-19 cases among cold-chain food handling and operating groups are likely related to occupational risk.
Surveillance results
Another survey, published in the same journal, analyzed almost 56 million frozen food-related samples between July 2020 and 2021.
From the 56 million samples, 1,455 were positive for SARS-CoV-2 nucleic acid. Out of 1,398 SARS-CoV-2-positive food and packaging materials, all but seven were imported.
Researchers said findings support speculation that cold-chain foods might act as the SARS-CoV-2 carrier, and food handlers or operators were at high risk of exposure to the virus.
The Coronavirus pandemic has impacted the global food system with direct and indirect consequences, causing widespread concern and economic hardship for consumers, businesses, and communities, although it is neither a food safety issue nor a foodborne disease.
In Hong Kong, more than 34,000 samples of foods and their packaging have been tested for the virus and less than 10 have been positive.
China launched a nationwide program to screen for SARS-CoV-2 contamination on packaged frozen food produced, either domestically or abroad, in July 2020.
Positive swabs came from seafood, poultry meat, and other foods. Outer packaging contamination by SARS-CoV-2 nucleic acid was much more common than inner packaging or the food itself.
Positive samples came from 11 European countries, six South American nations, nine Asian countries, two North American ones, and two African countries.
“The survival and recovery of SARS-CoV-2 in certain foods highlighted the importance of safe food handling practices in mitigating any public health concerns related to SARS-CoV-2-contaminated foods,” said researchers.
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