Viral Transport Medium: Can PBS Step Up in a Pinch?
The COVID-19 pandemic led to an unprecedented need for widespread testing globally. An essential component of testing is the viral transport medium (VTM) used to collect and transport nasal/throat swabs to labs for analysis. But global supply chain disruptions left many regions scrambling for VTM availability. Researchers in Kenya asked: Could common saline solutions effectively replace standard VTM for COVID-19 testing? Their findings highlight intriguing options for resource-limited settings.
What Exactly is Viral Transport Media and Why is it Needed?
VTM contains nutrients and stabilizers to maintain intact virus particles for reliable COVID-19 detection. Quality VTM ensures the sample integrity from collection through transport and analysis. Without VTM, the virus degrades over time, especially if unrefrigerated, leading to inaccurate or false negative results.
What Common Solutions Did Researchers Evaluate as Alternatives?
Facing shortages, the researchers systematically compared four media: standard commercial VTM, locally-produced VTM, phosphate buffered saline (PBS), and simple saline solution (0.9% sodium chloride). PBS and saline are attractive options due to wide availability, but some studies question their virus preservation ability.
How Did the Study Rigorously Assess and Compare these Media?
In a robust head-to-head test, standardized laboratory cultured SARS-CoV-2 virus was inoculated into each medium and stored for 7 days at freezing, refrigeration, room, and body temperatures. Every 24 hours, viral RNA was extracted and analyzed by PCR to precisely quantify the viral levels over time across conditions, providing an objective measure of each medium’s stability and preservation capacity.
What Were the Key Results of this Head-to-Head Media Comparison?
Excitingly, the study found little significant difference between commercial VTM gold standards and the common PBS and saline solutions in maintaining detectable viral RNA across storage times and temperatures tested. Additionally, locally-produced VTM performed on par with commercial VTM, offering a more sustainable option for expanded testing capacity in resource-limited settings.
What are the Practical Implications for COVID-19 Testing Globally?
This rigorous analysis demonstrates saline and PBS can effectively replace standard VTM for COVID-19 molecular testing after sample collection if needed. Especially promising, viral RNA remained reliably detectable for 7 days even at tropical room and body temperatures in all media. This suggests refrigerated transport may not be essential in warm climates lacking transport infrastructure, potentially expanding testing access.
However, the cultured viral samples used may exceed patient sample concentrations. Further real-world evaluations are warranted. For now, cold chain transport and rapid testing remain best practice whenever feasible to avoid false negatives.
This study reveals saline and PBS solutions as viable alternatives to standard VTM for COVID-19 molecular testing. The capacity to utilize readily available transport media enhances resilience against supply shortages and empowers expanded testing globally, especially in low-resource settings.
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References
Ngetsa C, Osoti V, Okanda D, Marura F, Shah K, Karanja H, Mugo D, Gitonga J, Mutunga M, Lewa C, Orindi B, Bejon P, Ochola-Oyier LI. Validation of saline, PBS and a locally produced VTM at varying storage conditions to detect the SARS-CoV-2 virus by qRT-PCR. PLoS One. 2023 Feb 13;18(2):e0280685. doi: 10.1371/journal.pone.0280685. PMID: 36780469; PMCID: PMC9924993.
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