Influence of Storage Conditions on SARS-CoV-2 Nucleic Acid Detection in Throat Swabs

Abstract

The detection of SARS-CoV-2 infection is the premise of quarantine. In many countries or areas, samples need to be shipped or inactivated before SARS-CoV-2 testing. In this study, we checked the influence of sample storage conditions on SARS-CoV-2 nucleic acid testing results, including sample inactivation time, storage temperature, and storage time. All of these conditions caused an increase in the cycle threshold values of the nucleic acid tests and led to the misclassification of at least 10.2% of positive cases as negative or suspected. The results highlight the importance of immediate testing of samples for SARS-CoV-2 nucleic acid detection.

Keywords: influence; SARS-CoV-2; nucleic acid detection; storage; throat swab.

Figure 1.

Distribution of cycle threshold (Ct) values for SARS-CoV-2 target genes ORF1ab and N before and after different treatments. Distribution of Ct values measured in 88 SARS-CoV-2–positive throat swab samples before and after (A) storage at room temperature for 1 or 2 days; (B) storage at 2°C–8°C for 1 or 2 days; (C) 1 or 2 freeze-thaw cycles; and (D) inactivation at 56°C for 30 or 60 minutes. Bars indicates mean ± SD. Abbreviations: BF, analysis before test conditions; IS, internal standard (human RNase P gene); NF, no fluorescence signal at the maximum number of cycles (45).