Value of in-house viral transport medium in breaking the bottlenecks for viral testing in Pakistan

Background: Maintenance of a steady supply of viral transport medium (VTM) for transporting clinical samples to the laboratory for viral testing is critical amid periods of viral outbreak. Hence, we prepared an in-house VTM and validated its capacity to preserve viral nucleic acids. Material and Methods: We used Phosphate-buffered saline (PBS) supplemented with sterile glycerol and a combination of antibiotics viz. vancomycin, colistin sulphate, amphotericin B and trimethoprim lactate, for our VTM formulation. For stability, antimicrobial efficacy and sterility evaluation, representative samples from each batch were selected. To validate our VTM, we tested clinical nasal swab samples transported in commercially available (Copan Italia S.p.A.) and in-house VTM, and compared both the media for viral nucleic acid recovery using Reverse transcriptase-polymerase chain reaction (RT-PCR). Results: A satisfactory evaluation of in-house VTM in terms of stability, antimicrobial efficacy and sterility was obtained. A total of 239 nasal swab samples were processed in both commercial and PBS VTM, of which 61 (25.5%) transported in commercial VTM were positive compared to 63 (26.4%) transported in PBS VTM. A comparison of Ct values in RT-PCR positive samples from both groups (n=61), showed Ct values of less than 25 in 14.7% samples from PBS VTM compared to 21.3% from commercial VTM. Whereas, more samples from PBS VTM (78.7%) compared to commercial VTM (73.8%) exhibited Ct values of more than 30. Our results showed that PBS VTM exhibited 100% sensitivity, 98.9% specificity, 96.8% positive predictive value and 100% negative predictive value. Conclusion: Our in-house prepared VTM was successfully validated and offers a readily available, cost-effective, and simpler to prepare alternative for diagnostic laboratories in low resource settings. Keywords: Viral transport medium, VTM, Viruses, RT-PCR