An article published on the medRxiv preprint platform by Wuhan University Central South Hospital and Wuhan Jinyintan Hospital on February 23 points out that 2019-nCoV testing by sputum samples is more accurate and convenient compared with pharyngeal swab samples.
Real-time reverse transcription polymerase chain reaction analysis (qRT-PCR)-based detection of viral nucleic acid sequences is the primary means of confirming the diagnosis of neo-CoV pneumonia, and the test samples are primarily pharyngeal swabs, which can easily lead to missed diagnoses if not collected properly, and the collection process is extremely risky for medical personnel. Appropriate sample selection is important for the diagnosis of respiratory viral infections, so it is necessary to find sample types with higher detection efficiency and precision.
This study obtained paired samples of pharyngeal swabs and sputum from 54 cases, extracted RNA and detected 2019-nCoV by qRT-PCR to compare the positivity rate between pharyngeal swabs and sputum specimens. The results revealed that the positive rates of 2019-nCoV in sputum specimens and pharyngeal swabs were 76.9% and 44.2%, respectively, and most patients (51.9%) had the same test results for pharyngeal and sputum specimens; however, a considerable number of patients (40.4%) had positive sputum specimens and negative pharyngeal swabs, and only a very small number of patients (7.7%) had negative sputum specimens and positive pharyngeal swabs, with sputum samples showing significantly higher positive rate of pharyngeal swab samples (P=0.001).
Distribution of qRT-PCR results of pharyngeal swabs and sputum samples from patients with suspected COVID-19
The detection rate of 2019-nCoV in sputum specimens was higher than that in pharyngeal swabs, which may be related to the fact that the novel coronavirus mainly invades and infects lower respiratory tract cells leading to clinical manifestations such as cough and pneumonia. Although the number of cases is small and additional discussion of bronchoalveolar lavage fluid and blood specimens is needed in the future, this study suggests the value of sputum for the detection of new coronaviruses, which may facilitate specimen selection and improve the accuracy of COVID-19 diagnosis.
