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Influence of storage conditions on SARS-CoV-2 nucleic acid detection in throat swabs.

Author(s): Li L, Li X, Guo Z, Wang Z, Zhang K, Li C, Wang C, Zhang S

Publication: J Infect Dis, 2020, Vol. , Page

PubMed ID: 32427340 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   This study investigated the effects of storage, freeze-thaw cycling, and deactivation on CT values and SARS-CoV-2 positivity in throat swab specimens. Eighty-eight throat swabs from patients with SARS-CoV-2 were placed in 3 mL transport media. Specimens were tested within 2 h of collection and the remainder was aliquoted into 96 well plates and then stored at 2-8°C or room temperature for 1-2 days, subjected to one or two freeze-thaw cycles (temperatures unspecified), and deactivated at 56°C for 30 or 60 min. RNA was extracted using a KingFisher Flex Purification System and amplified using the real-time RT-PCR 2019 Novel Coronavirus Detection Kit. Specimens were considered positive if amplification of both the ORF1ab and N-gene were observed with a CT≤40. Specimens were considered suspect if only one gene was amplified with CT≤40 and negative if neither gene had CT≤40.

   Summary of Findings:

   After storage at 2–8°C for 1 day, the mean CT increased by 0.66 and 13 specimens were no longer considered to be positive with seven specimens no longer showing amplification of either gene (negative) and six having amplification of only one gene (suspect). After 2 days at 2–8°C, the mean CT increased by 1.37 and 20 specimens were no longer considered to be positive (6 negative and 14 suspect). Similarly, storage for 1 or 2 days at room temperature resulted in an increase in the mean CT value of 0.78 and 1.30, respectively; and loss of positivity in 14 and 22 specimens, respectively. Of the specimens that were no longer considered positive, five were considered negative and 9 considered suspect after 1 day and eight considered negative and 14 suspect after 2 days. Freeze-thaw cycling once resulted in an increase in the mean CT value of 0.41 and a loss of positive status in 9 specimens (4 negative and 5 suspect) and freeze-thaw cycling twice resulted in a mean CT value increase of 0.81 and loss of positive status in 17 specimens (5 negative and 12 suspect). Inactivation at 56°C for 30 min resulted in an increase in the mean CT of 0.71 after 30 min and an increase of 0.64 after 60 min and loss of positive status in 15 (4 negative and 11 suspect) and 16 specimens (6 negative and 10 suspect) after 30 and 60 min, respectively.

   Biospecimens

   • Cell - Oral Cavity

   Preservative Types

   • None (Fresh)
   • Frozen

   Diagnoses:

   • Pneumonia/Respiratory Infection

   Platform:

   Analyte	Technology Platform
   RNA	Real-time qRT-PCR

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Storage	Storage temperature	2-8°C Room temperature
   Analyte Extraction and Purification	Incubation duration/condition	30 min at 56°C 60 min at 56°C
   Storage	Freeze/thaw cycling	0 cycles 1 cycle 2 cycles
   Storage	Storage duration	0 days 1 day 2 days

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