ABSTRACT
Birmingham University Turnkey laboratory is part of the Lighthouse network responsible for testing clinical samples under the UK government ‘ Test & Trace’ scheme. Samples are analysed for the presence of SARS-CoV-2 in respiratory samples using the Thermofisher TaqPath RT-QPCR test, which is designed to co-amplify sections of three SARS-CoV-2 viral genes. Since more recent information became available regarding the presence of SARS-CoV-2 variants of concern (S-VoC), which can show a suboptimal profile in RT-QPCR tests such as the ThermoFisher TaqPath used at the majority of Lighthouse laboratories, we analysed recently published data for trends and significance of the S-gene ‘dropout’ variant. Results: showed that: the population of S-gene dropout samples had significantly lower median Ct values of ORF and N-gene targets compared to samples where S-gene was detected on a population basis, S-gene dropout samples clustered around very low Ct values for ORF and N targets linked Ct values for individual samples showed that a low Ct for ORF and N were clearly associated with an S-dropout characteristic when conservatively inferring relative viral load from Ct values, approximately 35% of S-dropout samples had high viral loads between 10 and 10,000-fold greater than 1 × 10 6 , compared to 10% of S-positive samples. This analysis suggests that patients whose samples exhibit the S-dropout profile in the TaqPath test are more likely to have high viral loads at the time of sampling. The relevance of this to epidemiological reports of fast spread of the SARS-CoV-2 in regions of the UK is discussed.
ABSTRACT
Lateral flow devices are quickly being implemented for use in large scale population surveillance programs for SARS-CoV-2 infection in the United Kingdom. These programs have been piloted in city wide screening in the city of Liverpool, and are now being rolled out to support care home visits and the return home of University students for the Christmas break. Very little data exists comparing the performance of the UK lateral flow tests with gold standard PCR diagnostics, especially against comparable test populations such as the national Pillar 2 testing program in the United Kingdom. Here we utilise thousands of pillar 2 test data from our University of Birmingham test lab, and by extrapolation against the validate limit-of-detection of the lateral flow assay, provide a potential sensitivity for the test in a comparable low prevalence population captured in the pillar 2 program. Our data suggests the lateral flow assay should successfully capture around 85% of all PCR positive tests performed in our pillar 2 laboratory, and that a fully designed comparative study of lateral flow versus PCR testing is merited in a real life testing environment