Since last year, the cold chain has been regarded as an important part of the prevention and control of the new crown epidemic. The source of the Qingdao epidemic in October 2020 also points to the two dock workers who entered the cold chain site for transportation.

It is worth noting that 3 of the 71 dockers in the same batch did not wear masks for smoking, and 2 of them were infected. None of those wearing masks in accordance with the protection requirements were infected.

An article published in the latest issue of “China CDC Weekly” (China CDC Weekly) by the China CDC, Qingdao CDC and other teams Research articles have confirmed the possibility of the new coronavirus spreading to humans from the cold chain. In September 2020, two dock workers in Qingdao, China, were tested for asymptomatic infection with the new crown virus after routine screening of throat swabs. Genome sequencing results confirmed that the two were infected due to exposure to the outer packaging of cold chain products carrying the new coronavirus. Corresponding authors of the study include Gao Fu, academician of the Chinese Academy of Sciences and director of the Chinese Center for Disease Control and Prevention. Since the outbreak of the new crown, some have been imported from abroad New coronavirus nucleic acid was detected in the outer packaging of cold chain seafood products. Several waves of local outbreaks, especially the two outbreaks in Beijing’s Xinfa District and Dalian City, are all considered to be related to the first patient’s exposure to cold chain overseas products. Previous epidemiological investigations have proved this. However, because researchers have not been able to isolate live viruses, the spread of cold chain product viruses to humans cannot be confirmed.

The research team said that the investigation in this study isolated live viruses from cold chain products, which further confirmed that cold chain products spread to humans through long-distance transportation Possible.

Actually, on October 17th last year, the official website of the Chinese Center for Disease Control and Prevention announced that recently, the Chinese Center for Disease Control and Prevention was investigating the source of the new crown pneumonia in Qingdao. , Live virus was detected and isolated from positive samples of imported frozen cod carried by workers. This is the first time that the live new coronavirus has been isolated on the outer packaging of cold-chain food, and it has been confirmed that contact with the outer packaging contaminated by the new coronavirus can cause infection.

Starting from August 11, 2020, Qingdao will conduct nucleic acid testing every 14 days for high-risk groups, including those working in the processing, sales and shipment of frozen seafood . Two dockers belonging to the same company were screened on September 22 and September 24, 2020The new coronavirus is positive, and these cases are the source reports of Qingdao City for 151 days.

From September 8 (the last nucleic acid test) to 23, 2020, the two asymptomatic infected dock workers did not live in the high-risk area of ​​the epidemic, and did not live with Contact with patients in high-risk areas who are infected with the new coronavirus or have fever for unknown reasons. There were no imported cases in the communities where the two lived, and neither of them had contact with overseas returnees. During the period of suspected virus exposure, the two dockers both came into contact with frozen cod from abroad unloaded from Ship K: they were handled in two different storage warehouses between 20:00 on September 19, 2020 and 6:00 on September 20, 2020. Frozen cod. Through retrospective research, the researchers analyzed 71 Investigate the contact history of dockers transporting K-ship cold chain products and their behavior when loading frozen cod. The investigation found that the two infected dock workers had risky behaviors including smoking, wearing masks and exposing their noses. It is worth noting that both infected persons took off their masks and smoked, while none of the non-smokers were infected.

From July 2020, about 90 crew members have boarded the fishing trawler V (Trawler V). On September 3, 2020, the packaged frozen cod was transferred from the trawler V to the K ship. The crew of the V trawler took out the cod from their cold storage, transferred the cod to the K ship by a crane, and frozen the cod on the K ship (-18°C). The study believes that since the crew of the V ship has not received the new coronavirus nucleic acid test and there is no evidence that the crew of the K ship is infected with the new crown virus, the source of the new crown virus contamination on the frozen food packaging is most likely to come from the crew of the trawler V. However, due to the unknown infection status of the crew of V, the transmission chain cannot be clearly established at present.

The researchers performed a whole genome sequencing study on 2 case samples and 11 frozen cod samples with positive nucleic acid results. Compared with the Wuhan reference strain sequence, these 11 whole genomes have 12-14 nucleotide mutation sites, among which there are the same 12 nucleotide mutation sites. The researchers preliminary judged that the two dock workers were infected with the new coronavirus by loading and unloading frozen cod with contaminated outer packaging.

Six high viral load samples collected in frozen cod trays were used to further isolate the virus. The research team observed typical coronavirus particles under a cryo-electron microscope, which indicated that a live, infectious new coronavirus was isolated from the sample. The sequencing results also show that the virusThe positive result of the culture is not due to contamination. The research team believes that this research confirms the new crown The virus can spread to countries and regions over long distances through the international marine fishery trade, and the mode of transmission is similar to the spread of the new coronavirus among close contacts in the environment of polluted families and medical institutions. This poses a major public health challenge for countries and regions that have blocked the local spread of the new coronavirus.

The researchers proposed that first, the study found that when the contaminated packaging has a high virus load, the virus can survive at low temperatures for several weeks to several months (currently the longest The record is from July to September), the virus may still infect employees after several months or years of storage in the cold storage. Secondly, studies have shown that SARS-CoV-2 can survive in humid, low temperature and high salt environments. Therefore, it is necessary to further study the impact of environmental factors such as pH, salinity, temperature and humidity on the survival of the virus.

Researchers suggest that the management of the cold chain process should be strengthened globally to prevent new coronavirus contamination in the production of fish and meat. It is necessary to carry out regular nucleic acid screening of high-risk groups in order to detect infected persons at an early stage.

They also called on the international community to pay close attention to the cold chain spread of the new crown virus and establish an international response mechanism to prevent the new crown virus from being used in cold chain food production, marine fishing and processing. , Transportation and other links. At the same time, it is necessary to strengthen the sanitation and epidemic prevention knowledge training for practitioners and related professionals engaged in the outer packaging of imported seafood cold chain products, and further improve the formulation of standards for equipment and facilities related to the working environment of imported cold chain foods and the formulation of personal protection standards. In addition, the study also recommends that port workers be included in the high-risk groups for emergency vaccination.