Objective To establish SARS-CoV-2 nucleic acid detection method,and compare the difference of nucleic acid detection results between the upper and lower respiratory tract specimens of COVID-19 patients,so as to provide reference for clinical diagnosis of SARS-CoV-2 infection,selection of specimen types and improvement of nucleic acid positive detection rate. Methods The respiratory tract specimens of 31 patients with suspected COVID-19 were collected,and the real-time fluorescence quantitative RT-PCR method was used to detect the double-target (ORF1ab gene and N gene) nucleic acid of pharyngeal swabs and sputum specimens of those patients.The SARS-CoV-2 positive rate of different types of specimens was analyzed by chi square test. Results Of the 31 pharyngeal swab specimens of COVID-19 cases,26 were positive and 5 were negative,with a positive rate of 83.8%.Of the 31 sputum samples,29 were positive and 2 were negative,with a positive rate of 93.5%.There was no statistically significant difference in specimen test results (χ2=1.449,P＞0.05).There was no significant difference in the positive rate of pharyngeal swabs and sputum samples in patients with different onset time (P=0.669).The mean CT value of ORF1ab gene in pharynx swabs and sputum samples were compared (the number of cycles experienced when the fluorescence signal reached the set threshold).The mean CT value in pharynx swabs was 3.04 higher than that in sputum samples.The value of CT in N gene was 3.33 higher than that in sputum samples.One patient was negative in respiratory tract and positive in anal swab. Conclusion Pharyngeal swabs and sputum samples could be used for the detection of SARS-CoV-2 nucleic acid.The mean CT value of ORF1ab gene and N gene in sputum samples were lower than that in pharynx swabs,which was easier to detect,and was more advantageous for detecting SARS-CoV-2.In addition,for patients with negative nucleic acid test of respiratory tract specimens,further testing of gastrointestinal specimens was of great significance to patients' clinical judgment and disease prevention and control.
Key words
SARS-CoV-2 /
Real-time fluorescence quantitative RT-PCR /
CT value /
New infectious disease
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