Seafood in a Qingdao market Photo:

The Chinese city of Qingdao will test all imported refrigerated food after its government claimed to have proved that the Covid-19 virus can survive on frozen food packaging.

Microbiologists found that the virus could could survive for a long time under freezing conditions, Luan Xin, vice-mayor of Qingdao, said on Tuesday. They also found that the virus could be transmitted from objects to human.

For these reasons, Qingdao would increase its efforts in the next step of epidemic prevention and control, she said.

Earlier this month, 13 new confirmed cases emerged in Qingdao, which has a population of more than 11 million. Two health officials have been punished after the outbreak was traced to an inadequately disinfected hospital room.

The Qingdao Health Commission has identified nine patients out of all 532 close contacts of those infected as of Tuesday. These cases have already been reported.

The Chinese Center for Disease Control and Prevention recently identified and isolated the virus on the outer packaging of some imported frozen cod handled by logistic workers in Qingdao. The findings suggested that the packaging of refrigerated or cold chain products could spread the virus.

Qingdao would strengthen the control of imported cold chain food in three ways, Chen Wansheng, deputy director of Qingdao Municipal Government Office, said.

Those in direct contact with imported cold chain food in ports will be tested every three to five days while other workers in contact with the food will be tested once a week, Chen said. Wholesalers must report to the market supervision department a day before their purchased food arrives in the urban area. The government will also increase its monitoring of cold chain food production.

Whether the virus can be isolated from the frozen food depends on many factors, including the level of contamination and environmental temperature, Liu Peipei, deputy director of P3 Laboratory, Chinese Center for Disease Control and Prevention, wrote in a recent article. Viruses usually can live longer on frozen food during transport in the autumn than summer, Liu said.

The coronavirus can be spread with cold chain food across countries while those who contact the outer packaging of the food can be infected, according to Liu’s article.

Prior to this, Shenzhen Headquarters Office for Covid-19 Prevention and Control said in August that a sample collected from the surface of a pack of frozen chicken wings imported from Brazil tested positive. Those who had contacted the products tested negative but were required to undergo medical observation.

The office said it had checked all Brazilian frozen products in the city but had not found another contaminated sample. It urged the public to remain cautious when handling frozen meat and aquaculture products.

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Xu Yuenai is a Beijing-based columnist specializing in international relations.