Abstract
Background
As per the guidelines of the Indian Council of Medical Research, nasopharyngeal and oropharyngeal swabs in viral transport medium (VTM) are to be stored at 4 °C for less than 5 days and for more than 5 days at -70 °C. Samples are not transported or stored as per prescribed conditions because of the limitations, resulting in an apprehensive diagnosis. The aim of the study was to test the stability of the SARS-CoV-2 sample stored in VTM at different temperatures.
Methods
In this study, the stability of 21 positive and 9 negative samples for SARS-CoV-2 was evaluated in commercial VTM at different temperatures (-80 °C, -20 °C, 4 °C, and 25 to 30 °C). Stability was checked for up to 50 days in the above storage conditions at different intervals. PathoDetect™ and Hi-PCR® kits were used for the detection of the four genes of SARS-CoV-2. The Cycle Threshold (Ct) value for determining the positivity of samples for PathoDetect™ was < 40 and for Hi-PCR® was < 38.
Results
The SARS-CoV-2 confirmatory genes (RdRp and E genes) and the internal housekeeping gene remained detectable even on the 50th day of the study. The Ct of the RdRp and E genes were found to increase with storage duration, but all positive samples remained positive till the end of the study, or the Ct value remained below the cut-off level. The negative samples gave consistent results until the end of the study. When the differences in Ct values were compared between the days in a set of experiments, they were not significantly different except in a few samples.
Conclusion
The SARS-CoV-2 genetic materials in commercial VTM were stable at room temperature to -80 °C for 50 days.
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Data Availability
All relevant data are within the manuscript and its supplementary files.
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Acknowledgements
Authors are thankful to Dr. Chetram Meena, Technical Officer, Dr. Rajnish Gupta, Technical Assistant, Sh. Rajkumar, MTS for assisting in the experimental works the study.
Funding
This study was funded by Indian Council of Medical Research in the form of intramural grant and was awarded to Dr. S. S. Mohanty.
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SSM conceived and designed the study. SSM, RKS, AKS and MT wrote the protocol. RKS and SSM generated and analysed the data. SSM, RKS, AKS and MT wrote the report, and all authors contributed to the drafts before submission.
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The study was reviewed and approved by the Institutional Ethics Committee–Biomedical and Health Research, ICMR-NIIRNCD, Jodhpur, Rajasthan (Ref No. IEC-NIIRNCD-2021/trainee/8). Consent of all the participants were taken for the study.
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Swain, R.K., Mohanty, S.S., Thakor, M. et al. Assessment of thermal and temporal stability of SARS-CoV-2 samples using real-time qRT-PCR. Mol Biol Rep 50, 8565–8573 (2023). https://doi.org/10.1007/s11033-023-08740-7
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DOI: https://doi.org/10.1007/s11033-023-08740-7