Lack of sensitivity of an IVD/CE-labelled kit targeting the S gene for detection of SARS-CoV-2

Abstract

Objectives: New molecular tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are being rapidly launched in response to the coronavirus disease 2019 (COVID-19) pandemic. The aim of this study was to evaluate the analytical and clinical performance of the VIASURE SARS-CoV-2 S gene RT-PCR Kit on the BD Max™ system and to compare results with those obtained with the cobas® SARS-CoV-2 test on the cobas® 6800 system.

Methods: For testing the analytical performance, reference material was used. Clinical samples (n = 101) obtained from individuals with symptoms compatible with COVID-19 were studied. Oropharyngeal and nasopharyngeal swabs were collected by using either ESwab™ or UTM™ collection systems.

Results: When the analytical performance was evaluated, the sample containing the lowest SARS-CoV-2 concentration tested negative with the VIASURE test whereas results obtained with the cobas® test were found to be concordant with the results expected. Six out of the 101 clinical samples (5.9%) showed an inhibition with the VIASURE test. When analysing the remaining 95 clinical samples, 27 were found to be negative with both assays. Of 68 samples that were positive with the cobas® test, the VIASURE test missed 21 (30.9 %) samples. All of those 21 samples had shown Ct values ≥ 31 with the cobas® 6800 system. None of the samples tested positive with the VIASURE test and negative with the cobas® test.

Conclusions: The VIASURE test was impaired by a lack of sensitivity and a relatively high number of invalid results. When using the VIASURE test for routine testing, a significant number of COVID-19-positive samples would have been missed.

Keywords: COVID-19; Cobas; Diagnostics; Real-time RT-PCR; VIASURE.

Fig. 1

VIASURE SARS-CoV-2 S gene RT-PCR test results of COVID-19 samples diagnosed with the cobas® SARS-CoV-2 RT-PCR test. In three independent analyses, a total of 101 cobas® SARS-CoV-2 test-positive and -negative throat samples were tested with the VIASURE SARS-CoV-2 S gene test. Each dot represents a cobas® test-positive sample with the corresponding Ct value of target 1 (if target 1 was negative, target 2 is depicted). Both cobas® and VIASURE test-negative samples as well as inhibited samples in the VIASURE test are not depicted. The numbers of VIASURE test positives from cobas® test positives are shown below the corresponding dots above the abscissa. In the right upper corner of the figure an example of an amplification curve of the cobas® system of a sample that was negative in the VIASURE test is shown. The respective sample in the first analysis from Graz is marked with an asterisk. The horizontal line marks a Ct value of 31. It indicates the lowest Ct value at which conflicting test results between the VIASURE test and the cobas® test started to appear.

Fig. 2

Distribution of Ct values of SARS-CoV-2 RNA-positive pharyngeal swabs diagnosed with the cobas® 6800 system during 1 week of daily testing in Graz. The total number of quantitative PCR-positive samples detected during 1 week in the Graz laboratory is depicted below the corresponding dots above the abscissa. The horizontal line marks a Ct value of 31. It indicates the lowest Ct value, at which conflicting test results between the VIASURE test and the cobas® test started to appear (Fig. 1).