Comparison between nasopharyngeal swabs and saliva as reliable specimens for the diagnosis of SARS-CoV-2

Abstract

Introduction: The SARS-CoV-2 virus is a positive-strand RNA virus. The virus can also be detected in many different specimens as throat swabs, nasal swabs, sputum, saliva, blood, etc. Objective: The aim of this paper is to compare the reliability of different types of specimen collection, saliva and swabs samples for the detection of SARS-CoV-2. Material and Methods: A sample of 22 COVID-19 positive patients was selected. Paired samples from saliva, nasopharyngeal, oropharyngeal and nasopharyngeal + oropharyngeal swabs were collected on the 7th day after diagnosis. The hyssops and medium employed was IMPROSWAB and IMPROVIRAL NAT Medium, Germany. The sample evaluation was conducted through RT-PCR. The results were compared using Fisher’s exact test and ROC curve. The gold standard proposed in this paper was the nasopharyngeal + oropharyngeal swabs specimen. Results: The gold standard method detected 10 true positive cases, of which oropharyngeal swabs, nasopharyngeal swabs and saliva only detected three positive cases. Significant differences (Fisher’s exact test p = 0.003) were detected in the comparison between saliva and the gold standart proposed. The ROC curve analysis showed that saliva had an area under the curve of 0.650, with a 30% of sensibility. However, the nasopharyngeal and nasopharyngeal + oropharyngeal samples had an area under curve of 0.950 and 1.000, respectively, with a sensibility of 90% and 100%, respectively. Conclusion: Saliva samples are not a reliable specimen for SARS-CoV-2 RNA detection. In turn, the most reliable specimens are nasopharyngeal and nasopharyngeal + oropharyngeal samples collected by swabbing.

Keywords

• saliva, covid-19, sars-cov-2, sensibility, rt-pcr, nasopharyngeal swab, oropharyngeal swab