Assessment of thermal and temporal stability of SARS-CoV-2 samples using real-time qRT-PCR

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 degrees C for less than 5 days and for more than 5 days at -70 degrees 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 degrees C, -20 degrees C, 4 degrees C, and 25 to 30 degrees C). Stability was checked for up to 50 days in the above storage conditions at different intervals. PathoDetect (TM) and Hi-PCR (R) 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 PathoDetectT was < 40 and for Hi-PCR (R) 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 degrees C for 50 days.

Automated summary

This study evaluated the stability of SARS-CoV-2 samples stored in commercial VTM at different temperatures. The results showed that the genetic materials of SARS-CoV-2 remained stable for up to 50 days at room temperature to -80 degrees C.