Detection of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Is Comparable in Clinical Samples Preserved in Saline or Viral Transport Medium

Abstract

As the coronavirus disease 2019 (COVID-19) pandemic sweeps across the world, the availability of viral transport medium (VTM) has become severely limited, contributing to delays in diagnosis and rationing of diagnostic testing. Given that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA has demonstrated stability, we posited that phosphate-buffered saline (PBS) may be a viable transport medium, as an alternative to VTM, for clinical real-time quantitative PCR (qPCR) testing. The intra-individual reliability and interindividual reliability of SARS-CoV-2 qPCR were assessed in clinical endotracheal secretion samples transported in VTM or PBS to evaluate the stability of the qPCR signal for three viral targets (N gene, ORF1ab, and S gene) when samples were stored in these media at room temperature for up to 18 hours. We report that the use of PBS as a transport medium allows high intra-individual and interindividual reliability, maintains viral stability, and compares with VTM in the detection of the three SARS-CoV-2 genes through 18 hours of storage. This study establishes PBS as a clinically useful medium that can be readily deployed for transporting and short-term preservation of specimens containing SARS-CoV-2. Use of PBS as a transport medium has the potential to increase testing capacity for SARS-CoV-2, aiding more widespread screening and early diagnosis of COVID-19.

Figure 1

Ct counts from replicate samples from two individuals. Black/gray points are from Subject 1, and dark blue/light blue points are from Subject 2. Dark points and light points indicate the two types of transport media, phosphate-buffered saline (PBS) and viral transport medium (VTM), respectively. The horizontal axis, comparative pair, refers to replicate samples (ie, same individual, same length of storage time).

Figure 2

Comparison of Ct values in real-time quantitative PCR assays for three severe acute respiratory syndrome coronavirus 2 genes for samples transported in viral transport medium (VTM) or phosphate-buffered saline (PBS). A total of 26 samples that were transported in the two media are shown: N (A), ORF1ab (B), and S (C). The correlations are 0.93 for the N, 0.83 for ORF1ab, and 0.91 for the S, and all are significant (P < 0.05).