Korean J Fam Pract.  2021 Jun;11(3):164-169. 10.21215/kjfp.2021.11.3.164.

Usefulness of Sputum and Pharyngeal Swab Specimens for Diagnosis of Coronavirus Disease 2019

• Yun HS
• Jang DS
• Lee SH

• KMID: 2516772
• DOI: http://doi.org/10.21215/kjfp.2021.11.3.164

Abstract

Background
Various specimens are possible for the diagnosis of COVID-19, but previous studies comparing samples were small studies with hospitalized patients. The purpose of this study is to help diagnose COVID-19 in the future by comparing the sputum and nasopharyngeal swabs from a COVID-19 screening clinic and accordingly analyzing the clinical characteristics.
Methods
A total of 3,390 people from a COVID-19 screening clinic at a hospital in Daegu were included in the study. McNemar’s test and Cohen’s Kappa statistics were performed to compare sputum and nasopharyngeal swabs and to evaluate the degree of agreement. After classifying participants into groups based on the duration of their symptoms (within one week vs. more than one week), the Mann-Whitney U test was used to compare the Ct values of each gene of the two specimens.
Results
The sensitivity of the sputum specimen was 91.6%, which was lower than that of nasopharyngeal swabs, 94.4%, but there was no significant difference. In addition, Cohen’s Kappa coefficient was 0.917, showing very high agreement. The Ct value of each gene in the two specimens was significantly higher in the group whose symptom duration was longer than 1 week regardless of the type of specimen.
Conclusion
The sensitivity of nasopharyngeal swabs was not significant but higher compared to that of sputum, so they are recommended as the preferred specimens for the diagnosis of COVID-19. In addition, the result of self-collected sputum also showed very high agreement with result of nasopharyngeal swabs, so self-collected sputum can be recommended as a secondary alternative specimen for COVID-19 diagnosis.

Keyword

COVID-19; Sputum; Nasopharyngeal Swab; SARS-CoV-2; Sensitivity; Reverse Transcriptase Polymerase Chain Reaction