Objective: To investigate a SARS-CoV-2 epidemic reported in Rongcheng City, Weihai, Shandong Province. Methods: The SARS-CoV-2 nucleic acid positive patients and their close contacts were investigated, and the whole genome sequencing and genetic evolution analysis of 9 variant viruses were carried out. An infection source investigation and analysis were carried out from two sources of home and abroad, and three aspects of human, material and environment. Results: A total of 15 asymptomatic infections were reported in this epidemic, including 13 cases as employees of workshop of aquatic products processing company, with an infection rate of 21.67% (13/60). Two cases were infected people's neighbors in the same village (conjugal relation). The first six positive persons were processing workers engaged in the first process of removing squid viscera in the workshop of the company. The nucleic acid Ct value of the first time were concentrated between 15 and 29, suggesting that the virus load was high, which was suspected to be caused by one-time homologous exposure. The whole genome sequence of 9 SARS-CoV-2 strains was highly homologous, belonging to VOC/Gamma (Lineage P.1.15). No highly homologous sequences were found from previous native and imported cases in China. It was highly homologous with the six virus sequences sampled from May 5 to 26, 2021 uploaded by Chile. The infection source investigation showed that the company had used the squid raw materials captured in the ocean near Chile and Argentina from May to June 2021 over the last 14 days. Many samples of raw materials, products and their outer packages in the inventory were tested positive for nucleic acid. Conclusion: This epidemic is the first local epidemic caused by the VOC/Gamma of SARS-CoV-2 in China. It is speculated that the VOC/Gamma, which was prevalent in South America from May to June 2021, could be imported into China through frozen squid.
目的： 对山东省威海荣成市报告一起新型冠状病毒肺炎疫情进行溯源调查。 方法： 对新型冠状病毒（SARS-CoV-2）核酸检测阳性者及其密切接触者进行调查，对9株病毒毒株进行全基因组测序及遗传进化分析；从国内外两个源头，人、物和环境三个方面开展溯源调查。 结果： 本次疫情累计报告15例无症状感染者，包括某水产品加工公司车间13例，感染率为21.67%（13/60）；感染者的同村邻居2例（夫妻关系）。初次检出的6例感染者为从事清除鱿鱼内脏首道工序工人，首次咽拭子核酸检测Ct值为15~29，病毒载量高，疑为同源一次性暴露所致。9株病毒毒株全基因组序列高度同源，属于VOC/Gamma（P.1.15进化分支），与我国既往本土和输入病例均不同源；与智利上传的2021年5月5—26日采样的6条病毒序列高度同源。溯源结果显示，该公司近14日内使用过2021年5—6月在智利、阿根廷附近海域捕获的鱿鱼原材料；库存原材料、产品及其外包装多处采样核酸检测呈阳性。 结论： 本次疫情是我国首起由SARS-CoV-2 VOC/Gamma引起的本土聚集性疫情，可能为南美洲地区2021年5—6月期间流行的VOC/Gamma通过冷冻鱿鱼传入我国。.