VIROLOGY Virus
Influenza A Influenza A RSV A RSV B
RT 3+
3+ 2+ 3+
Week 1
37°C 3+
3+ 2+ 3+
RT 2+
2+ 1+ 2+
Week 9 37°C
Negative Negative Negative Negative
RT 2+
2+ 1+ 2+
Week 10 37°C
Negative Negative Negative Negative
Table 1. Results from the lateral-flow tests for each of the specimens from weeks 1, 9 and 10, for influenza A, influenza B, RSV A and RSV B at RT and 37°C. Scoring: 3+ (very strong band), 2+ (strong band), 1+ (weak band), ± (very weak band), negative (no visible band).
This small study aims to determine i) if a POC scheme is required and will be beneficial to healthcare providers testing for influenza viruses, RSV and SARS- CoV-2 in a POC setting, ii) the stability of the selected viruses over a period of 10 weeks in VTM, and iii) the efficacy of antigen and molecular testing methods for these viruses.
Methodology
n Questionnaire The questionnaire posed five questions, as follows:
1. What respiratory viruses does your laboratory test for?
2. What sample volume is required to run all respiratory virus assays in your laboratory?
3. Does your laboratory type Influenza virus (Influenza A and Influenza B)?
4. Does your laboratory sub-type Influenza A virus?
A
5. Does your laboratory type respiratory syncytial virus (RSV A and RSV B)?
The questionnaire was sent to participants enrolled in the ‘SARS-CoV-2 Point of Care’ and ‘Molecular Detection of SARS-CoV-2’ EQA schemes, in addition to those testing for influenza viruses, RSV and enteroviruses enrolled in the ‘Molecular Detection of Respiratory Viruses’ EQA scheme.
n Feedback Responses from the questionnaire in the three EQA schemes shows that the majority of laboratories test for all three of the respiratory tract infection viruses (Fig 1). This shows that there is a clinical need for a POC test that incorporates SARS-CoV-2, influenza (A and B) and RSV (A and B) testing in the same panel.
n Stability testing study Specimens positive for influenza virus, B
RSV and SARS-CoV-2 were made in VTM at various concentrations. Specimens were incubated at room temperature (RT) and at 37°C, and were tested at one week intervals for 10 weeks. Antigen testing as well as molecular testing was carried out on each sample.
The intensity of the bands on the lateral-flow tests were graded based on their strength.
The influenza A strain was the A/ Slovenia/2903/2015 (H1N1) strain. The influenza B was the B/Phuket/3073/2013 (B/Yamagata lineage) strain. The RSV A and B strains were taken from clinical isolates circulating within the last five years. The SARS-CoV-2 strain was Omicron BA.2.
Results
n Antigen testing The lateral-flow tests were able to correctly identify the viruses for the duration of the stability testing. Specimens stored at ambient RT demonstrated greater viral stability over 10 weeks compared to those kept at 37°C (Table 1).
The SARS-CoV-2 test produced the same intensity (3+) of results throughout the duration of stability testing (Fig 2A). The RSV B test for the RSV B-positive sample decreased in intensity from week one (3+) compared to week nine (2+) (Fig 2B).
n Molecular testing
The nucleic acid concentration remained unaffected over the course of the stability
Fig 2. A) Lateral-flow results for SARS-CoV-2 at week 5 and week 8; B) Lateral-flow results for RSV B at week 1 and week 9. 46 MAY 2024
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