SARS-CoV-2 live virus culture and sample freeze-thaw stability

Abstract

AbstractThe COVID-19 pandemic has presented unique diagnostic challenges including the need to store and test large number of samples for clinical and research studies. While SARS CoV-2 diagnosis relies on RT-qPCR and antigen testing, live virus culture remains an important surrogate for viral “infectiousness”, as we previously described in “SARS-CoV-2 Antigen Tests Predict Infectivity Based on Viral Culture: Comparison of Antigen, PCR Viral Load and Viral Culture Testing on a Large Sample Cohort” (Clin Microbiol Infect, 2022,PMC9293398). Live virus isolation and characterization has also been important to the SARS CoV-2 research community, to assess viral fitness, cellular tropism, and live virus neutralization, particularly with the emergence of new variants. Many clinical and research studies make use of samples that are frozen in transport media and investigated at later dates. The effect of freezing on RT-qPCR results is well established. However, the effect of freeze-thaw on viral viability has not been. Here, we therefore examined the effect of freeze-thaw on viral culture isolation from a large number of clinical samples that were split, and then cultured either fresh or after being frozen for 7 or 17-18 days. Samples represented the range of viral loads (genome copies/mL) observed in our patient population. We found that freeze-thaw did not significantly affect viral culture isolation. Therefore, the ability to assess infectiousness of samples previously frozen in transport medium appears to be maintained.