To explore the role of guanidine salt-containing virus inactivated storage tubes in improving the safety and accuracy of COVID-19 nucleic acid assay.

Ten samples that were positive for nucleic acid of 4 COVID-19 cases diagnosed in Guangzhou Women and Children's Medical Center in February, 2020 were studied. The samples were eluted and aliquoted using the storage solution of guanidine salt--containing inactivated storage tube and a certain brand of pathogen delivery tube, and then stored at room temperature for 12 h, 24 h and 48 h, respectively and transfered to the refrigerator at -80 ℃ before testing. The results of qPCR were compared between the two groups, and the differences were statistically analyzed.

The same amount of virus was put into two different sampling tubes and immediately subjected to qPCR, with higher detection of nucleic acid in inactivated tubes containing guanidine salt. In the high viral load samples, the correlation between the detection results of the two types of tubes at different time periods was higher. The CT values of the inactivated storage tubes were smaller, and the results are statistically significant (P<0.05) after 24 h at room temperature. In the samples with medium viral load, the measurement results of the two kinds of sampling tubes are not statistically significant (P>0.05), but the measured results varied with time, and the amplification curve of inactivated storage tube group appeared earlier and the CT values were smaller. When detecting the low viral load samples, there was a large difference (P<0.01 after 24 h) between the amplification results of the two groups and the inactivated tubes were able to obtain positive results within 24 h of placement time, while the results of pathogen delivery tubes were unstable and only within a short storage time could they obtain the positive results. The detection rate of inactivated storage tube group was higher than that of pathogen delivery tube group, with better reproducibility of the target three gene assays, indicating a stronger ability of viral nucleic acid.

In the COVID-19 nucleic acid sampling process, the use of virus inactivation storge tubes containing guanidine salt, on the one hand, can immediately inactivate the virus after sampling, greatly reduce the risk of laboratory exposure to infection and can achieve room temperature preservation and transportation of samples, reduce the cost of transshipment, conducive to the delivery of the grassroots unit. On the other hand, it can maintain the stability of viral nucleic acid, make it easier to detect low copy number viruses, and reduce false negatives which has a positive significance for ensuring the accuracy of COVID-19 nucleic acid detection.