key: cord-0955880-j6w49f18
authors: Dierks, Sascha; Bader, Oliver; Schwanbeck, Julian; Groß, Uwe; Weig, Michael S.; Mese, Kemal; Lugert, Raimond; Bohne, Wolfgang; Hahn, Andreas; Feltgen, Nicolas; Torkieh, Setare; Denker, Fenja R.; Lauermann, Peer; Storch, Marcus W.; Frickmann, Hagen; Zautner, Andreas Erich
title: Diagnosing SARS-CoV-2 with Antigen Testing, Transcription-Mediated Amplification and Real-Time PCR
date: 2021-05-29
journal: J Clin Med
DOI: 10.3390/jcm10112404
sha: 59704bce3477482841f848ab8dc4ea2979311cea
doc_id: 955880
cord_uid: j6w49f18

This study was performed as a head-to-head comparison of the performance characteristics of (1) two SARS-CoV-2-specific rapid antigen assays with real-time PCR as gold standard as well as (2) a fully automated high-throughput transcription-mediated amplification (TMA) assay and real-time PCR in a latent class analysis-based test comparison without a gold standard with several hundred samples in a low prevalence “real world” setting. Recorded sensitivity and specificity of the NADAL and the LumiraDx antigen assays and the Hologic Aptima SARS-CoV-2 TMA assay were 0.1429 (0.0194, 0.5835), 0.7644 (0.7016, 0.8174), and 0.7157 (0, 1) as well as 0.4545 (0.2022, 0.7326), 0.9954 (0.9817, 0.9988), and 0.9997 (not estimable), respectively. Agreement kappa between the positive results of the two antigen-based assays was 0.060 (0.002, 0.167) and 0.659 (0.492, 0.825) for TMA and real-time PCR. Samples with low viral load as indicated by cycle threshold (Ct) values > 30 were generally missed by both antigen assays, while 1:10 pooling suggested higher sensitivity of TMA compared to real-time PCR. In conclusion, both sensitivity and specificity speak in favor of the use of the LumiraDx rather than the NADAL antigen assay, while TMA results are comparably as accurate as PCR, when applied in a low prevalence setting.

The Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2), causing the Corona Virus Disease 2019 (COVID- 19) pandemic, was first reported in Wuhan, China, in 2019 [1] . Due to the subsequent rapid global spread, the availability of both rapid and reliable diagnostic approaches became an issue of concern. To match this need, the first in-house real-time PCR protocols were soon provided [2] .

However, as traditional real-time PCR requires sophisticated laboratory infrastructure and skilled technical laboratory assistance, there was considerable demand for cartridgebased or otherwise fully-automated, point-of-care-testing (POCT) like devices for the molecular detection of SARS-CoV-2 RNA. Cepheid's (Sunnyvale, CA, USA) GeneXpert system and Abbott's (Chicago, IL, USA) ID Now system were the first broadly available assays showing good performance characteristics in a Cochrane analysis published as early as in August 2020 [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] . Additionally, Luminex's (Austin, TX, USA) cartridge-based ARIES PCR system allowed fully automated testing comparably early [14, 15] . Another fully automated CE certified and FDA cleared approach for the detection of SARS-CoV-2 nucleic acids from upper respiratory tract specimens is the Hologic Aptima SARS-CoV-2 TMA assay on the Hologic Panther platform [16] [17] [18] [19] [20] [21] [22] [23] [24] . The "Panther" assay is based on transcription-mediated amplification (TMA) of two targets and provides qualitative results only, without the possibility to gain further information on the virus load of positive samples, unlike with standard real-time PCR-based SARS-CoV2 assays based on Ct (cycle threshold) value assessment.

Although easy to apply with little training effort for laboratory personnel, such fullyautomated POCT-like molecular approaches still have considerable limitations. Firstly, many of them [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] are poorly suited for large scale assessments. Secondly, there has been a shortage of consumables from the beginning of the SARS-CoV-2 pandemic. Thirdly, traditional immunochromatographic antigen-based rapid tests were less expensive, and finally, highly sensitive molecular assays tend to detect prolonged residual shedding of SARS-CoV-2 RNA with questionable relevance in terms of transmission risk [25] [26] [27] [28] . Although, accordingly, development efforts were soon directed towards traditional antigen-based rapid tests, performance characteristics of first respective approaches left a lot of room for improvement. In the above-mentioned Cochrane analysis from August 2020 [3] , sensitivity of available SARS-CoV-2 antigen tests ranged from 0% to 94% with average sensitivity of 56.2% (95% confidence interval (0.95 CI) 29.5% to 79.8%) and average specificity of 99.5% (0.95 CI 98.1% to 99.9%). Despite the comparably good specificity, according to Bayes' theorem [29] , application in low prevalence settings can lead to both problems regarding the positive as well as the negative predictive value [30] , thus limiting the practical application of such early designs for public health interventions.

To identify optimized strategies of antigen-based rapid testing for SARS-CoV-2, numerous studies [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] have been performed and partly summarized in additional reviews [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] after those first, quite disillusioning trials [3] . Despite persisting sensitivity issues and resulting in quite variable diagnostic reliability [57] , antigen-testing was broadly used in the reaction to the second SARS-CoV-2 wave in many countries [58] . In case of implementation outside laboratory infrastructure under tropical conditions, environmental conditions such as room temperature and air moisture have also been described to potentially interfere with test reliability [59] .

For gradual improvement of the diagnostic quality of rapid SARS-CoV-2 tests, headto-head comparisons have been suggested in order to optimize diagnostic solutions [36] . In times of increasing spread of virus mutants, it is of further interest to assess effects of mutations on the reliability of antigen testing similar to the S gene target failure, as observed in real-time PCR for the B1.1.7 lineage [60] .

In the study conducted here, we sought to individually evaluate the NADAL COVID-19 Ag Test (Nal von Minden GmbH, Regensburg, Germany) and a microfluidic immunofluorescence assay (SARS-CoV-2 Ag Test, LumiraDx GmbH, Cologne, Germany) as well as a head-to-head assessment against real-time PCR. Individual [38, 61] and combined [62] assessments of these assays had yielded promising yet still imperfect results in previous preliminary studies [62] . However, the quoted study [62] had been performed with a small sample number of just 74 PCR-positive and 26 PCR-negative specimens yet the resulting preliminary results suggested specificity close to 100% for both rapid assays. While sensitivity of the LumiraDx assay was 50.0% in total and 100% in samples with RNA copy numbers > 10 6 copies/mL, the values were 24.3% and 76.2% for the NADAL assay, respectively [62] .

Further, the fully automated "Panther" TMA assay, for which high sensitivity had been reported in previous studies [16] [17] [18] [19] [20] [21] [22] [23] [24] , was also included in the assessment. While real-time PCR was considered as a reference standard or "gold standard" for the comparison with the antigen assays [29] , indirect accuracy estimation by latent class analysis (LCA) [29, 63] was chosen for the evaluation of the TMA assay, for which similar or higher sensitivity in comparison to real-time PCR could be expected [16] [17] [18] [19] [20] [21] [22] [23] [24] . A larger number of several hundred non-preselected samples were analyzed in a low-prevalence setting for both the gold standard-based assessment of the antigen tests and the LCA-based assessment of the TMA platform, to assess the performance of the assays in a diagnostic "real world" scenario.

A total of 444 employees of the University Medical Center Göttingen were assessed by rapid antigen testing and PCR for respiratory carriage of SARS-CoV-2. Samples were included if they had been analyzed in parallel by at least one antigen test and at least one real-time PCR assay as described below. If these minimum requirements were not fulfilled, the sample was excluded from the assessment. Real-time PCR was considered as the diagnostic reference standard or "gold standard" for this assessment [29] .

Further, the Hologic Aptima SARS-CoV-2 TMA assay was validated with 322 diagnostic nasopharyngeal swabs from patients of the University Medical Center Göttingen in comparison to the Genesig COVID-19 Real-Time PCR assay as detailed below in a test comparison without a gold standard [29, 63] . Both assays were run in parallel in order to avoid a bias due to loss of sensitivity after sample storage. In order to assess the effects of pooling, 1:10 pools of 18 samples with low viral load (Ct values > 30 in Genesig real-time PCR) were comparatively assessed by both the Genesig real-time PCR and TMA assessment.

For both test comparison approaches, cycle threshold (Ct) values of the real-time PCR assays were included in the assessments.

No data on the participating individuals were collected in the course of this surveillance screening for organizational reasons, an admitted violation of the Standards for Reporting of Diagnostic Accuracy Studies (STARD) [64] .

The applied rapid antigen-based or automated molecular SARS-CoV-2 tests comprised the NADAL COVID-19 Ag Test (Nal von Minden GmbH, Regensburg, Germany), the microfluidic immunofluorescence assay LumiraDx SARS-CoV-2 Ag Test (LumiraDx GmbH, Cologne, Germany), and the Hologic Aptima SARS-CoV-2 TMA assay (Hologic Deutschland GmbH, Wiesbaden-Nordenstadt, Germany). All these assays were applied according to the manufacturers' guidelines [16] [17] [18] [19] [20] [21] [22] [23] [24] 38, 61, 62] . Comparative PCR testing as gold standard for the antigen test assessment was performed either by the Roche Cobas SARS-CoV-2 PCR (Roche, Basel, Switzerland) [13, 65] , the Genesig Real-Time PCR Coronavirus (COVID-19) assay (Primerdesign Ltd., Chandlers Ford, UK) [66] , or the Cepheid Xpert Xpress SARS-CoV-2 PCR (Cepheid, Sunnyvale, CA, USA) [13, 14] . The choice of the PCR assay depended on availability in the diagnostic routine. For the assessment of the Hologic Aptima SARS-CoV-2 TMA assay [16] [17] [18] [19] [20] [21] [22] [23] [24] in a test comparison without a gold standard [29, 63] , the Genesig Real-Time PCR Coronavirus (COVID-19) assay (Primerdesign Ltd., Chandlers Ford, UK) [66] was applied only as competing assay.

In a descriptive approach, sensitivity and specificity of the rapid test assays was calculated applying the PCR results as gold standard for the antigen test and applying latent class analysis (LCA) [29, 63] for the comparison of the TMA assay with real-time PCR. Predictive values were provided based on calculated sensitivity, specificity and prevalence.

The software Stata/IC 15.1 for macOS 64-bit Intel (College Station, TX, USA) was used. For the assessment of the agreement between antigen as well as TMA testing results and real-time PCR results, Cohen's kappa was calculated with the categories poor (below 0.00), slight (0.00-0.20), fair (0.21-0.40), moderate (0.41-0.60), substantial (0.61-0.80) and almost perfect (0.81-1.00) as described [67] . Matching of positive and negative results with Ct-values of real-time PCR was descriptively assessed.

The study was ethically approved by the institutional ethics board of the University Medical Center Göttingen (Application number/project identification code 21/05/20 from 21 May 2020), allowing the fully anonymized use of residual sample materials for test comparison purposes.

The LumiraDx SARS-CoV-2 Ag Test was applied with 444 individuals. Of these, 437 tested negative, and 7 tested positive. Sensitivity and specificity with 0.95 confidence intervals and PCR as gold standard were calculated as 0.4545 (0.2022, 0.7326) and 0.9954 (0.9817, 0.9988), respectively (Table 1) . 

The kappa coefficient with 0.95 confidence interval between the two rapid tests was calculated as 0.060 (0.002, 0.167) ( Table 1 ).

Low numbers of positive samples allowed a superficial assessment of Ct values only. However, as indicated in Table 2 , Ct values ≥ 30 were associated with falsely negative results in the assessed antigen tests. 

When comparing the TMA assay with the Genesig real-time PCR assay using LCA, both assays showed excellent specificity close to 100%. Agreement of positive results as indicated by Cohen's kappa was substantial [67] . Calculated sensitivity of the TMA assays (71.6%) was slightly better than the sensitivity of the real-time PCR assay (65.4%) with the sample population assessed (Table 3) . 

The mean value of Ct values of the Genesig real-time PCR for samples concordantly positive in the TMA assay and the real-time PCR assay was 30.8. For samples positive in real-time PCR but negative in the TMA assay, this mean value was 38.8 and thus close to the detection threshold (Table 4 ). 

In case of 1:10 pooling of 18 samples with low viral loads (Ct > 30 in the Genesig real-time PCR), TMA was considerably more sensitive (83.3%) than Genesig real-time PCR (33.3%) with only slight concordance [67] (Table 5) . Samples with positive results in Genesig real-time PCR after pooling showed Ct values smaller than 36 without exemption, resulting in a mean Ct value of 38.2 after pooling ( Table 6 ). 

By applying LCA with the data from the test comparison of TMA and Genesig realtime PCR testing, a prevalence of 9.95% was calculated. Based on the sensitivities and specificities as estimated for the different compared test assays, reduced positive but high negative predictive values of the antigen tests were observed, as expected for a low prevalence setting. Additionally, due to the calculated high specificity, the positive predictive values were high for the molecular assays (Table 7) . Table 7 . Predictive values as calculated for the assessed assays in the low prevalence setting in which they were evaluated.

Positive 

In this study we assessed the diagnostic performance of the antigen-based rapid test assays NADAL and LumiraDx under "real-world" conditions. As expected from previous assessments [38, 62, 63] , the applied antigen test assays were more likely to identify samples with higher pathogen load, as indicated by Ct values < 30, while samples with higher Ct values were missed. This result is not surprising and confirms the suitability of rapid antigen testing for the identification of individuals with high pathogens loads and, therefore an associated high likeliness of transmission only.

More interesting is the merely slight agreement between the positive antigen testing results when directly comparing the two antigen test assays. Certainly, this result is affected by the low number of positive results in the population assessed, nevertheless, it suggests a high variance regarding the positive results that can be expected in a low prevalence community, depending on the antigen test applied.

The recorded sensitivities of the antigen tests were slightly lower in this "real-world" assessment but nevertheless in a similar range with previous evaluation studies [38, 62, 63] . Regarding specificity however, only the LumiraDx approach showed similar values compared with previous evaluation studies [62, 63] . The NADAL assay, in contrast, scored considerably worse [38, 63] , with specificity as low as 76.4% in the low prevalence population assessed. Due to Bayes' theorem [29] , this will lead to a considerable proportion of falsely positive test results and thus to a poor positive predictive value when applied in a low prevalence setting. So, based on both sensitivity and specificity results, the use of the LumiraDx assay is preferable compared to the NADAL assay.

Furthermore, comparable diagnostic accuracy of Genesig real-time PCR and Hologic Aptima TMA assay, both targeting ORF-1 sequences of SARS-CoV-2 [16] [17] [18] [19] [20] [21] [22] [23] [24] 66] , was demonstrated with clinical samples of patients of the University Medical Center Göttingen. The results are in line with previous studies [16] [17] [18] [19] [20] [21] [22] [23] [24] 66] and confirm the suitability of the Hologic Panther TMA platform for fully automated, high-throughput SARS-CoV-2 screening. The low sensitivity of both assays within the assessed sample population is most likely due to the high proportion of samples with low viral loads close to the diagnostic detection threshold. In case of pooling of samples with low viral loads, moderately better sensitivity of the TMA approach compared to the Genesig real-time PCR assay was demonstrated. Despite this better sensitivity, the limitation of lacking semi-quantification when applying the TMA technology remains, as no Ct values are provided. So, TMA assessment may be a powerful tool for high-throughput initial screening for SARS-CoV-2 but is unsuitable for follow-up assessments.

The study has a number of limitations. Firstly, although several hundred individuals could be included in the assessment, the proportion of positives was quite low, making any calculations regarding sensitivity doubtful. As expected for the antigen tests due to the low prevalence, lower positive than negative predictive values were calculated. For the molecular assays, positive predictive values were good due to their high specificity. Furthermore, the combination of low sample count and low prevalence prevented a more sophisticated comparison of rapid test positivity with semi-quantification, as indicated by Ct values in PCR. Secondly, not all samples could be tested with all assays for logistical reasons, which limits their comparability. Thirdly, ethical clearance allowed fully anonymized use of patient samples for the applied test comparison purposes only, so patient-specific features can neither be shown nor assessed.

Despite the above-mentioned limitations, the presented "real world" assessment suggests superiority of the LumiraDx assay compared to the NADAL assay when applied in a low prevalence setting, based on both sensitivity and specificity considerations. Infections with low viral load, however, will be missed by both of them. In contrast, acceptable sensitivity and diagnostic accuracy similar to real-time PCR, even in the case of 1:10 pooling, could be shown for the Hologic Aptima SARS-CoV-2 TMA assay for highthroughput screenings.

Other than in previous assessments with pre-selected positive and negative samples [63] , our assessment provides a "real-life experience" in a low prevalence setting, suggesting that test accuracy might vary under such conditions compared to the results of standardized study settings. Large confidence intervals, which admittedly limit the interpretability of the data, are due to financial restrictions of investigator-initiated studies such as the one presented here. Of course, generously funded studies have the advantage of larger sample sizes, which in turn will result in lower 0.95 CI-intervals as suggested recently [63] .

Cross-reactions due to usually unknown co-infections are always possible in assessments in real-life situations, which describe the diagnostic performance of test assays that can actually be expected in contrast to possible performance under idealized, standardized study conditions. Accordingly, real-world studies are indispensable because they show how unstable standardized performance results may be. Because there are no standardized conditions under real-world conditions, real-world data are very much needed in order to recognize the limits of applied diagnostic assays. Therefore, they provide an indispensable addition to standardized evaluation studies rather than just an acceptable weakness. Because low prevalence is the standard in the COVID-19 pandemic due to preventive countermeasures, it makes sense to accept a small number of positive samples in the interest of a realistic assessment. This is the only way to make realistic conclusions about the reliability of the test results. 

A pneumonia outbreak associated with a new coronavirus of probable bat origin

Rapid, point-of-care antigen and molecular-based tests for diagnosis of SARS-CoV-2 infection. Cochrane Database Syst

Comparison of Abbott ID Now and Abbott m2000 Methods for the Detection of SARS-CoV-2 from Nasopharyngeal and Nasal Swabs from Symptomatic Patients

Comparison of Abbott ID Now, DiaSorin Simplexa, and CDC FDA Emergency Use Authorization Methods for the Detection of SARS-CoV-2 from Nasopharyngeal and Nasal Swabs from Individuals Diagnosed with COVID-19

Clinical Evaluation of Three Sample-to-Answer Platforms for Detection of SARS-CoV-2

Performance of Abbott ID Now COVID-19 Rapid Nucleic Acid Amplification Test Using Nasopharyngeal Swabs Transported in Viral Transport Media and Dry Nasal Swabs in a New York City Academic Institution

Detection of SARS-CoV-2 by Use of the Cepheid Xpert Xpress SARS-CoV-2 and Roche cobas SARS-CoV-2 Assays

Test Agreement between Roche Cobas 6800 and Cepheid GeneXpert Xpress SARS-CoV-2 Assays at High Cycle Threshold Ranges

Multicenter Evaluation of the Cepheid Xpert Xpress SARS-CoV-2 Test

Multi-center evaluation of cepheid xpert®xpress SARS-CoV-2 point-of-care test during the SARS-CoV-2 pandemic

Detection of low levels of SARS-CoV-2 RNA from nasopharyngeal swabs using three commercial molecular assays

Comparison of Cepheid Xpert Xpress and Abbott ID Now to Roche cobas for the Rapid Detection of SARS-CoV-2

Evaluation of the automated cartridge-based ARIES SARS-CoV-2 Assay (RUO) against automated Cepheid Xpert Xpress SARS-CoV-2 PCR as gold standard

Clinical performance of Roche cobas 6800, Luminex ARIES, MiRXES Fortitude Kit 2.1, Altona RealStar, and Applied Biosystems TaqPath for SARS-CoV-2 detection in nasopharyngeal swabs

Comparison of the Quidel Sofia SARS FIA Test to the Hologic Aptima SARS-CoV-2 TMA Test for Diagnosis of COVID-19 in Symptomatic Outpatients

Fully automated detection and differentiation of pandemic and endemic coronaviruses (NL63, 229E, HKU1, OC43 and SARS-CoV-2) on the Hologic Panther Fusion

High-Throughput Transcriptionmediated amplification on the Hologic Panther is a highly sensitive method of detection for SARS-CoV-2

Evaluation and Comparison of the Hologic Aptima SARS-CoV-2 Assay and the CDC 2019-nCoV Real-Time Reverse Transcription-PCR Diagnostic Panel Using a Four-Sample Pooling Approach

Comparison of the analytical sensitivity of seven commonly used commercial SARS-CoV-2 automated molecular assays

Performance Characteristics of a High-Throughput Automated Transcription-Mediated Amplification Test for SARS-CoV-2 Detection

Specificity and positive predictive value of SARS-CoV-2 nucleic acid amplification testing in a low-prevalence setting

Analytical and Clinical Comparison of Three Nucleic Acid Amplification Tests for SARS-CoV-2 Detection

Evaluation of the Aptima™ transcription-mediated amplification assay (Hologic ® ) for detecting SARS-CoV-2 in clinical specimens

Type I and Type III Interferons-Induction, Signaling, Evasion, and Application to Combat COVID-19

Prolonged SARS-CoV-2 RNA shedding: Not a rare phenomenon

Factors Associated With Prolonged Viral RNA Shedding in Patients with Coronavirus Disease 2019 (COVID-19)

Differences of Severe Acute Respiratory Syndrome Coronavirus 2 Shedding Duration in Sputum and Nasopharyngeal Swab Specimens Among Adult Inpatients with Coronavirus Disease

On detection thresholds-a review on diagnostic approaches in the infectious disease laboratory and the interpretation of their results

Testergebnisse richtig einordnen. Dtsch. Ärzteblatt

Comparison of the SARS-CoV-2 Rapid antigen test to the real star Sars-CoV-2 RT PCR kit

Low performance of rapid antigen detection test as frontline testing for COVID-19 diagnosis

Comparison of automated SARS-CoV-2 antigen test for COVID-19 infection with quantitative RT-PCR using 313 nasopharyngeal swabs, including from seven serially followed patients

Evaluation of a novel antigen-based rapid detection test for the diagnosis of SARS-CoV-2 in respiratory samples

Rapid SARS-CoV-2 antigen detection assay in comparison with real-time RT-PCR assay for laboratory diagnosis of COVID-19 in Thailand

Evaluation of a SARS-CoV-2 rapid antigen test: Potential to help reduce community spread?

Head-to-head comparison of SARS-CoV-2 antigen-detecting rapid test with self-collected nasal swab versus professional-collected nasopharyngeal swab

Performance of a Point-of-Care Test for the Rapid Detection of SARS-CoV-2 Antigen. Microorganisms

Comparison of Rapid Antigen Tests for COVID-19

Potential Use of Antigen-Based Rapid Test for SARS-CoV-2 in Respiratory Specimens in Low-Resource Settings in Egypt for Symptomatic Patients and High-Risk Contacts

Head-to-Head Comparison of Rapid and Automated Antigen Detection Tests for the Diagnosis of SARS-CoV-2 Infection

Real-life validation of the Panbio™ COVID-19 antigen rapid test (Abbott) in community-dwelling subjects with symptoms of potential SARS-CoV-2 infection

Performance of a rapid antigen test in the diagnosis of SARS-CoV-2 infection

Think of the Children: Evaluation of SARS-CoV-2 Rapid Antigen Test in Pediatric Population

Head-to-head comparison of SARS-CoV-2 antigen-detecting rapid test with professional-collected nasal versus nasopharyngeal swab

Evaluation of Analytical Performance of Seven Rapid Antigen Detection Kits for Detection of SARS-CoV-2 Virus

Testing for SARS-CoV-2 (COVID-19): A systematic review and clinical guide to molecular and serological in-vitro diagnostic assays

Detection of COVID-19: A review of the current literature and future perspectives

Diagnostic Testing for Severe Acute Respiratory Syndrome-Related Coronavirus 2: A Narrative Review

Laboratory Testing Methods for Novel Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2)

Laboratory diagnosis of SARS-CoV-2: Available approaches and limitations

COVID-19 diagnostics in context

Biosensors: Frontiers in rapid detection of COVID-19

Karunasagar, I. Detection technologies and recent developments in the diagnosis of COVID-19 infection

Rapid Response to Pandemic Threats: Immunogenic Epitope Detection of Pandemic Pathogens for Diagnostics and Vaccine Development Using Peptide Microarrays

A rapid review of recent advances in diagnosis, treatment and vaccination for COVID-19

Rapid point-of-care antigen and molecular-based tests for the diagnosis of COVID-19 infection

Recommendations for use of antigenic tests in the diagnosis of acute SARS-CoV-2 infection in the second pandemic wave: Attitude in different clinical settings

Implementing COVID-19 (SARS-CoV-2) Rapid Diagnostic Tests in Sub-Saharan Africa: A Review

S-variant SARS-CoV-2 lineage B1.1.7 is associated with significantly higher viral loads in samples tested by ThermoFisher TaqPath RT-qPCR

High-Sensitivity SARS-CoV-2 Nucleocapsid Immunoassay to Aid Diagnosis of Acute COVID-19 at the Point of Care: A Clinical Performance Study

Comparative Clinical Performance of Four SARS-CoV-2 Rapid Antigen Tests and Their Correlation to Infectivity In Vitro

Random effects models in latent class analysis for evaluating accuracy of diagnostic tests

STARD 2015 guidelines for reporting diagnostic accuracy studies: Explanation and elaboration

Comparison of SARS-CoV-2 detection from nasopharyngeal swab samples by the Roche cobas 6800 SARS-CoV-2 test and a laboratory-developed real-time RT-PCR test

Molecular Testing of SARS-CoV-2 Infection from Blood Samples in Disseminated Intravascular Coagulation (DIC) and Elevated D-Dimer Levels

The measurement of observer agreement for categorical data

We are grateful to Yvonne Laukat and Svenja Schiegl for their excellent technical assistance.

The authors declare no conflict of interest.