基于PCR循环阈值的SARS-CoV-2奥密克戎变异株的实验室分析

Laboratory analysis of the SARS-CoV-2 Omicron variant based on PCR cycle threshold

目的分析新型冠状病毒感染人群的鼻拭子和咽拭子标本的循环阈(Ct)值,为流行病学调查和临床预测等提供一定的理论依据。方法对2022年4月1日至7月31日本实验室接收的SARS-CoV-2核酸阳性人群的鼻拭子和咽拭子标本,运用磁珠法进行核酸提取,用实时荧光定量PCR检测SARS-CoV-2核酸的ORF1ab基因和N基因两个靶标,分析两类标本中两个靶标的Ct值。Ct值差异用独立样本t检验,以P<0.05为差异有统计学意义。结果SARS-CoV-2核酸阳性标本401例,男性243例、女性158例(男女比例1.54∶1);SARS-CoV-2核酸阳性人员年龄分布为7个月~91岁,中位数为39岁;临床分型为普通型31例,轻型281例,无症状感染者89例。同时采鼻拭子和咽拭子的106例,两类标本ORF1ab基因(t=7.728,P<0.001)和N基因(t=7.504,P<0.001)Ct值差异均有统计学意义。在同一人不同时间送检鼻拭子或咽拭子的73例标本中,采样时间间隔≤48h的标本26例,两次Ct值差值的绝对值>2的标本占61.54%(16/26),末次Ct值≤30的标本占61.5%(16/26);采样时间间隔>48h的标本56件,两次Ct值差值的绝对值>2的标本占82.1%(46/56),末次Ct值>30的标本占98.2%(55/56)。结论SARS-CoV-2奥密克戎变异株感染者的临床分型以轻型为主;鼻拭子标本的病毒载量高于咽拭子;采样时间间隔≤48h的标本,若Ct值快速下降且末次Ct值≤30,大多为新发感染人员;若末次Ct值>30则大多为复阳人员。Ct值仅有一定的提示作用,对于COVID-19人群的临床情况预测、感染者当下状态及何时参与社会活动,要根据其临床情况连同实验室结果进行评估。

Objective To analyze the cycle threshold(Ct)values of nasal swab and throat swab specimens from a population with COVID-19 infection,and to provide a certain theoretical basis for epidemiological investigation and clinical prediction.Methods Nasal swab and throat swab specimens received from the populations with positive nucleic acid of SARS-CoV-2 received in this laboratory from April 1 to July 31,2022,were subjected to nucleic acid extraction using the magnetic bead method,and the ORF1ab gene and the N gene as the two targets of SARS-CoV-2 nucleic acid were detected by real-time fluorescence quantitative PCR.The Ct values for the two targets were analyzed in the two types of specimens.The difference in Ct values was tested by independent sample t test,and the difference was considered statistically significant at P<0.05.Results A total of 401 cases of positive nucleic acid specimens of SARS-CoV-2 were found,including 243 males and 158 females(male to female ratio of 1.54∶1).The age distribution of persons with positive nucleic acid for SARS-CoV-2 ranged from 7 months to 91 years old,with a median age of 39 years.The clinical types were 31 cases of general type,281 cases of mild type,and 89 cases of asymptomatic infections.In the 106 cases of both nasal and throat swabs taken,the difference in Ct values for the ORF1ab gene(t=7.728,P<0.001)and the N gene(t=7.504,P<0.001)between the two types of specimens was statistically significant.In the 73 cases of nasal or throat swab specimens from the same person sent for testing at different times,a total of 26 specimens with sampling intervals≤48h,61.54%(16/26)of the specimens with the absolute value of the difference between the two Ct values>2 and 61.5%(16/26)of the specimens with the final Ct value≤30.A total of 56 specimens were collected at intervals>48h.The absolute value of the difference between the two Ct values was>2 in 82.1%(46/56)the specimens,and the final Ct value was>30 in 98.2%(55/56)of the specimens.Conclusion The clinical type of SARS-CoV-2 Omicron variant infected persons is mainly mild.Nasal swab specimens has higher viral loads than throat swabs.Specimens with a sampling interval of≤48h are mostly newly infected if the Ct value decreases rapidly and the final Ct value is≤30.If the final Ct value is>30,most people are again positive.Ct value has only a certain suggestive role.The prediction of clinical conditions of the population with COVID-19,the current status of the infected person and when to participate in social activities is assessed on the basis of the clinical situation together with laboratory results.