Title : Are your nasopharyngeal swabs stored in good condition?
Abstract:
Background: Every year, Influenza A (FluA), Influenza B (FluB) and Respiratory Syncytial Virus (RSV) affect our communities and increase the number of patients in our health systems. Symptoms are similar to those of SARS-CoV-2, so diagnosis is essential to initiate an appropriate treatment and surveillance. Also, epidemiological studies can help to understand the progress of the infection. To achieve this, molecular techniques, such as real-time PCR, have become essential. High amounts of samples or retrospective studies may need the use of samples stored at different conditions and inadequate storage conditions may have a negative impact. This work provides information about the stability of nasopharyngeal swabs (NP) in Viral Transport Medium (VTM) for FluA, FluB and RSV stored at different conditions.
Methods: Twenty-eight negative FluA, FluB and RSV NP samples in VTM (Vircell, Spain) were used in this study. All samples were mixed into one pool and divided into 7 aliquots. One of them served as a negative control. The others were enriched (each) with different concentrations of viral cultures from ATCC (Table 1) to obtain two positive samples for each pathogen.
Table 1. Positive samples and virus concentration used in the study
|
Target virus |
ATCC culture |
Copies/µL |
|
Influenza A (FluA) |
VR-95PQ™ A/Puerto Rico/8/34 |
Low Positive: 1.25 Positive: 5 |
|
Influenza B (FluB) |
VR1804PQ™ B/Florida/4/2006 |
Low Positive: 6 Positive: 20 |
|
Human Respiratory Syncytial Virus (RSV) |
VR26PQ™ |
Low Positive: 3 Positive: 10 |
Table 2. Time and temperature conditions used for storage conditions
|
Temperature |
Time |
|
25ºC |
1 day |
|
2 days |
|
|
4ºC |
3 days |
|
6 days |
|
|
-20ºC |
8 days |
|
30 days |
|
|
6 months |
Each condition was extracted in triplicate with the MagDEA Dx SV kit, using the magLEAD® 12gC instrument (Precision System Science Co.) and analysed with VIASURE SARS-CoV-2, Flu & RSV Real Time PCR Detection Kit (Certest Biotec S.L) in triplicate on CFX96™ Real-Time PCR Detection System (Bio-Rad). The results were compared with the data obtained on the first day (0 hours).
Results: All positive samples were detected in all conditions and matrices. No amplifications were observed in negative samples. There were no major differences compared with the data obtained on the first day. However, a Cq delay of around 1 unit was observed in all pathogens when samples were stored 2 days at 25ºC. For this reason, this storage condition would not be recommended.
Conclusions: Positive FluA, FluB and RSV nasopharyngeal swabs collected in VTM can be stored at 25°C for up to 1 day, 4°C for up to 6 days, or frozen at -20°C for up to 6 months, without impacting on their detection by real-time PCR. Samples stored at 25ºC for longer than one day could get degraded.
Audience take away:
- Audience will know about the impact of different storage conditions for nasopharyngeal swabs to detect respiratory virus such us Influenza, RSV and SARS-CoV-2.
- Biological samples storage should be a matter of concern. Inadequate storage conditions can impact on the results of later analysis.
- This study can help the audience to improve their storage conditions for biological samples. This can help to optimize the storage space, allowing to adopt a systematic work routine according to the laboratory needs.
