Evaluation of Using Direct Viral Transport Medium Samples without Nucleic Acid Isolation for SARS-CoV-2 Diagnosis by RT-PCR.

Background: Diagnosis with reverse transcriptase polymerase chain reaction (RT-PCR) test is a very important step for the control of the COVID-19 pandemic. The aim of this study is to compare the RT-PCR results of the samples taken directly from the viral transport medium (VTM) without extraction with the RT-PCR results of two different extraction methods, one automated and the other manual, in the diagnosis of COVID-19.

Methods: Among the respiratory tract samples sent to Sakarya Training and Research Hospital Microbiology Laboratory for COVID-PCR study, 20 negative and 43 positive samples with different cycle threshold (CT) values were included in the study. Both manual nucleic acid isolation with the vNAT isolation kit (Bioeksen, Turkey) and automatic nucleic acid isolation with the EZ1 Virus Mini Kit v2.0 in the isolation device were performed simulta-neously from the patient samples included in the study and the results were compared.

Results: The mean Ct values of the samples were found to be 21.58 using manual vNAT as the extraction method, 17.63 using the automated magnetic bead method, and 21.45 in PCR from direct VTM without extraction. When the automatic magnetic beads extraction method was taken as the reference method, the sensitivity of direct PCR was 97.3%, the specificity was 95%, the positive predictive value was 97.3%, and the negative predictive value was 95%. Phi coefficients were found to be 0.927 between vNAT and direct PCR, 1 between vNAT and EZ1, and 0.922 between direct PCR and EZ1.

Conclusions: Direct PCR has advantages such as eliminating RNA extraction and purification steps, providing a shorter detection time, and using less labor and less consumables without reducing the diagnostic accuracy. It is thought that this method can help as a useful process management for the control of the epidemic in countries with limited resources.