Objectives: With the continuous generation of new variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the pressure of epidemic prevention and control continues to increase in China. Omicron with stronger infectiousness, immune escape ability and repeated infection ability spread to many countries and regions around the world in a short period of time. China has also successively reported cases of imported Omicron infections. This study aims to understand the epidemiological characteristics of Omicron variant via analyzing the epidemiological characteristics of imported patients with Omicron in Hunan Province, and to provide reference for preventing and controlling the imported epidemics.
Methods: The clinical data of imported patients with coronavirus disease 2019 admitted to Hunan Province from December 16 to December 31, 2021 were retrospectively collected. The epidemiological information, general information, clinical classification, clinical symptoms, vaccination status, and lung CT were analyzed. Nasopharyngeal swabs and blood samples were collected. Virus nucleic acid was detected by magnetic beads method using SARS-CoV-2 detection kit. Ct values of ORF1ab gene and N gene were compared between asymptomatic infected patients and confirmed patients. The specific IgM and IgG antibodies were detected by chemiluminescence assay using SARS-CoV-2 IgM test kit and SARS-CoV-2 IgG test kit, respectively. Ct values of IgM and IgG antibodies were compared between asymptomatic infected patients and confirmed patients.
Results: Seventeen patients with Omicron variant infection were treated in Hunan, including 15 confirmed patients (5 common type and 10 mild type) and 2 asymptomatic infection patients. The 17 patients were all Chinese, they were generally young, and 16 were male. There were 9 patients with diseases. Of them 3 patients had respiratory diseases. All 17 patients had completed the whole process of vaccination, but only one person received a booster shot of SARS-CoV-2 vaccine. The clinical manifestations of the patients were mild, mainly including dry/painful/itchy throat, cough, and fatigue. The total protein and creatine in the asymptomatic infection and confirmed cases infected with Omicron variant were all within the normal range, but other biochemical indicators were abnormal. There were the significant differences in C-reactive protein and fibrinogen between asymptomatic infection and confirmed patients (both P<0.05). There were more patients with elevated C-reactive protein in confirmed patients than without confirmed ones. The detection rate of specific IgM and IgG antibodies on admission was 100%, and there was no significant difference in the specific antibody levels between asymptomatic infection and confirmed patients (P>0.05). There were no significant differences in Ct values of ORF1ab gene and N gene (21.35 and 18.39 vs 19.22 and 15.67) between the asymptomatic infection and the confirmed patients (both P>0.05). Only 3 patients had abnormal lung CT, showing a small amount of patchy and cord-like shadows. One of them had no abnormality on admission but had pulmonary lesions and migratory phenomenon after admission.
Conclusions: The patients with Omicron variant tend to be young people and have milder clinical symptoms, but the viral load is high and the infectiveness is strong. Therefore, the timely identification and effective isolation and control for asymptomatic infections and confirmed patients with mild symptoms are extremely important. In terms of epidemic prevention and control, the government still needs to strengthen the risk control of overseas input, adhere to normalized epidemic prevention and control measures, to effectively control the source of infection, cut off the route of transmission, and protect vulnerable people.
目的: 严重急性呼吸综合征冠状病毒2(severe acute respiratory syndrome coronavirus 2，SARS-CoV-2)又称新型冠状病毒，其新变异株不断产生，中国疫情防控压力持续增加。具有更强传染性、免疫逃逸能力和重复感染能力的Omicron变异株在短时间内传播至全球多个国家和地区，中国也陆续报道境外输入的Omicron变异株感染病例。本研究旨在通过分析湖南省Omicron变异株境外输入感染者的流行病学特征，更好地了解Omicron变异株的流行特点，为有效预防、控制境外输入疫情提供科学依据。方法: 回顾性收集2021年12月16日至31日湖南省长沙市收治的新型冠状病毒肺炎境外输入病例的临床资料，分析病例的流行病学史、一般情况、临床分型、临床症状、SARS-CoV-2疫苗接种情况及肺部CT影像等资料。采集鼻咽拭子及血液标本，利用SARS-CoV-2检测试剂盒通过磁珠法进行病毒核酸检测，比较无症状感染者和确诊患者ORF1ab基因和N基因的Ct值差异；特异性IgM、IgG抗体分别采用SARS-CoV-2 IgM检测试剂盒和SARS-CoV-2 IgG检测试剂盒通过化学发光法检测，比较无症状感染者和确诊患者特异性抗体IgM抗体和IgG抗体的差异。结果: 共收治17例Omicron变异株境外输入感染者，其中确诊15例(普通型5例、轻型10例)、无症状感染者2例。17例Omicron变异株感染者均为中国籍，年龄总体偏年轻，男性16例。9例患者有基础疾病，其中3例患者为呼吸系统疾病。17例感染者均已完成SARS-CoV-2疫苗全流程接种，但仅有1人接种了SARS-CoV-2疫苗加强针。患者临床表现较轻，主要表现为咽喉干/痛/痒、咳嗽、乏力。Omicron变异株感染的无症状感染者和确诊患者的总蛋白质和肌酸均在正常参考值范围内，但其他生化指标均出现异常，无症状感染者与确诊患者间仅C反应蛋白和纤维蛋白原差异具有统计学意义(均P<0.05)，确诊患者中C反应蛋白升高者较多。入院时特异性IgM、IgG抗体检出率为100%，无症状感染者与确诊患者间特异性抗体水平差异无统计学意义(P>0.05)。无症状感染者和确诊患者ORF1ab基因的Ct值分别为21.35和18.39，N基因的Ct值分别为19.22和15.67，核酸Ct值差异无统计学意义(P>0.05)。仅3例患者肺部CT存在异常，表现为少量斑片状、条索状影，其中1例入院时未见异常，入院后出现肺部病变并呈现游走性现象。结论: Omicron变异株感染者有年轻化趋势且临床症状较轻，但病毒载量高、传染性强，因此对无症状感染者和表现轻微症状感染者的及时识别和有效隔离、管控极其重要；在疫情防控上，政府仍需加强境外输入的风险管控，坚持常态化疫情防控措施，以有效控制传染源、切断传播途径、保护易感人群。.
Keywords: Omicron variant; coronavirus disease 2019; epidemiological characteristics; imported case; severe acute respiratory syndrome coronavirus 2.