Evaluation of Commercially Available Viral Transport Medium (VTM) for SARS-CoV-2 Inactivation and Use in Point-of-Care (POC) Testing

Abstract

Critical to facilitating SARS-CoV-2 point-of-care (POC) testing is assurance that viruses present in specimens are inactivated onsite prior to processing. Here, we conducted experiments to determine the virucidal activity of commercially available Viral Transport Mediums (VTMs) to inactivate SARS-CoV-2. Independent testing methods for viral inactivation testing were applied, including a previously described World Health Organization (WHO) protocol, in addition to a buffer exchange method where the virus is physically separated from the VTM post exposure. The latter method enables sensitive detection of viral viability at higher viral titre when incubated with VTM. We demonstrate that VTM formulations, Primestore^® Molecular Transport Medium (MTM) and COPAN eNAT™ completely inactivate high-titre SARS-CoV-2 virus (>1 × 10⁷ copies/mL) and are compatible with POC processing. Furthermore, full viral inactivation was rapidly achieved in as little as 2 min of VTM exposure. We conclude that adding certain VTM formulations as a first step post specimen collection will render SARS-CoV-2 non-infectious for transport, or for further in-field POC molecular testing using rapid turnaround GeneXpert platforms or equivalent.

Keywords: SARS-CoV-2; diagnostic; inactivation; virucidal.

Figure 1

Normalized viable cell count (per 1000) at Day 5 of culture following neutralization of SARS-CoV-2 in viral transport media at serial dilution. Count of viable Vero E6 cells is using NucBlue stain (normalized to a count of 1000 cells), when using the WHO method at low viral load (A,B), and high viral load (C–E), diluted in 10-fold series. Viable cell count at Day 5 culture following neutralization and recovery of SARS-CoV-2 using the BEx method is indicated at low viral load (F–H), and high viral load (I–K), diluted in five-fold series. Incubation in media is indicated by colour (grey hexagon: negative control; red square/triangle(up)/triangle (down): positive [control(triplicate)], circle (pink): Primestore^® MTM, (purple) COPAN™ eNAT, (blue) Qiagen AVL, square (khaki) COPAN™ UTM, (maroon) HCY-CV-19UTM, diamond (green) Sterigene^®, diamond (gold) heat-inactivation). Incubation in media only for the WHO method is indicated by the dotted line connecting data points. Significant differences in median cell count (of quadruplicate measurements) above cell counts observed for control wells positive for SARS-CoV-2 are represented by asterisks corresponding to the colour of each medium at each point of serial dilution (faded asterisks indicate incubation in media alone; ND, test not done).