DNA remains stable in a freezer for extended periods
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SUPPORTED
the evidence backs this
refutedsupported
the weight of evidence
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Peer-reviewed studies establish that viral and cellular DNA remains stable and shows little to no degradation when stored in freezers for extended periods ranging from several months to over two years.
Wastewater-based monitoring has been widely implemented worldwide for the tracking of SARS-CoV-2 outbreaks and other viral diseases. In many surveillance programmes, unprocessed and processed wastewater samples are often frozen and stored for long periods of time in case the identification and tracing of an emerging health threat becomes necessary. However, extensive sample bioarchives may be difficult to maintain due to limitations in ultra-freezer capacity and associated cost. Furthermore, the stability of viruses in such samples has not been systematically investigated and hence the usefulness of bioarchives is unknown. In this study, we assessed the stability of SARS-CoV-2, influenza viruses, noroviruses and the faecal indicator virus, crAssphage, in raw wastewater and purified nucleic aacid extracts stored at -80 °C for 6-24 months. We found that the isolated viral RNA and DNA showed little signs of degradation in storage over 8-24 months, whereas extensive decay viral and loss of qPCR signal was observed during the storage of raw unprocessed wastewater. The most stable viruses were noroviruses and crAssphage, followed by SARS-CoV-2 and influenza A virus. Based on our findings, we conclude that bioarchives comprised of nucleic acid extracts derived from concentrated wastewater samples may be archived long-term, for at least two years, whereas raw wastewater samples may be discarded after one year.
Background/Objectives: The surveillance of viral strain evolution is needed during prophylactic HPV vaccination programs against cervical cancer and necessitates safely archiving and storing cervical samples while maintaining the long-term stability of HPV DNA to carry out molecular diagnosis. The present proof-of-concept study aimed to assess DNA stability for HPV molecular detection from veils resuspended in a universal transport medium (UTM) and conserved at different temperatures after long-term storage. Methods: The detection and quantification of HPV DNA were evaluated in female genital secretions self-collected using veils and conserved in Cyt-All® UTM at −30 °C, +4 °C, and +25 °C after long-term 27-month storage. Results: A slight degradation of the ubiquitous single-copy cellular DNA TOP3 gene was assessed using multiplex real-time PCR (BMRT Human Papillomavirus Genotyping Real Time PCR Kit, Bioperfectus Technologies Co., Ltd., Taizhou, Jiangsu, China) at positive temperatures (+4 °C and +25 °C) but not at a frozen temperature (−30 °C) after 27 months of storage. Nevertheless, HPV DNA preservation was sufficient at the three storage temperatures to detect and quantify HPV DNA, with a similar rate of HPV detection, a similar level of cumulative HPV viral loads, high sensitivity and specificity, and perfect concordance in HPV genotype detection after the long period of 27 months of storage. Finally, the conservation of genital samples for a prolonged period in the Cyt-All® medium, even at room temperature, allows for the detection and quantification of any HPV and HR-HPV with high accuracy. Conclusions: The combination of veil-based self-sampling of female genital secretions and their elution and conservation in UTM may be used in the field to carry out longitudinal molecular epidemiology surveys of circulating HPV.
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