Stability of SARS-CoV-2 in phosphate-buffered saline for molecular detection. (Special Issue: Diagnostic testing for severe acute respiratory syndrome coronavirus 2 and lessons from this pandemic.)

ABSTRACT

This study evaluated the stability of differing viral loads of SARS-CoV-2 over 28 days stored at room temperature, 4 degrees Celsius, -20 Celsius, or -80 Celsius. For the high concentration of SARS-CoV-2, regardless of storage conditions, 100% of samples were detected by qRT-PCR through day 28. At room temperature, median cycle threshold (CT) values for lower titers for both N1 and N2 targets remained consistent through day 28, fluctuating less than 1 median CT. For lower concentrations of virus, storage at room temperature was associated with reductions of positivity beginning at day 7, and by day 28, 0% of samples were detected for N1. Storage at room temperature was the least stable of all environmental conditions tested, with 54.2% of negative PCR results. At 4 degrees Celsius, there was minimal change in CTs over time at the higher viral concentration. For lower titers, CTs increased by 2.1 CTs for N1 and 2.6 CTs for N2 over the 28 days. At -20 degrees Celsius, lower titers of virus fluctuated slightly more, increasing by 3 CTs. Storage of SARS-CoV-2 in PBS at -20 degrees Celsius was the second least stable condition, accounting for 37.5% of negative PCR results. Storage at -80 degrees Celsius showed the greatest stability, with all samples detected throughout the 28 days and 1.5 median CTs for both N1 and N2 targets. Here, this study shows that the stability of SARS-CoV-2 can be maintained at 4 degrees Celsius for up to a month when -80 degrees Celsius storage is not available. At viral loads of >5,000 copies/ml corresponding to >75% of positive samples recovered in the clinical lab to date-different storage temperatures did not have a substantial impact on the ability to detect SARS-CoV-2 when stored in PBS.