Performance of the LIAISON® SARS-CoV-2 Antigen Assay vs. SARS-CoV-2-RT-PCR.

We aimed to evaluate the LIAISON® SARS-CoV-2 antigen assay (DiaSorin), comparing its performance to real-time polymerase chain reaction (RT-PCR) for the detection of SARS-CoV-2 RNA. 182 (110 PCR-positive and 72 PCR-negative) nasopharyngeal swab samples were taken for the detection of SARS-CoV-2. RT-PCR and antigen assay were performed using the same material. The sensitivity and specificity of the antigen assay were calculated for different cut-offs, with RT-PCR serving as the reference method. Stored clinical samples that were positive for other respiratory viruses were tested to evaluate cross-reactivity. One third (33/110, 30%) were falsely classified as negative, while no false positives were found using the 200 TCID50/mL cut-off for the SARS-CoV-2 antigen as proposed by the manufacturer. This corresponded to a sensitivity of 70% (60-78%) and a specificity of 100% (94-100%). Lowering the cut-off for positivity of the antigen assay to 22.79 or 57.68 TCID50/mL increased the sensitivity of the method, reaching a sensitivity of 92% (85-96%) vs. 79% (70-86%) and a specificity of 81% (69-89%) vs. 99% (91-100%), respectively. The antigen assay reliably detected samples with high SARS-CoV-2 viral loads (≥106 copies SARS-CoV-2/mL), while it cannot differentiate between negative and low positive samples. Cross-reactivity toward other respiratory viruses was not detected.

Analytical and clinical performances of seven direct detection assays for SARS-CoV-2.

Background: Direct detection tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that bypass complicated nucleic acid/antigen purification steps are promising tools for the rapid diagnosis of coronavirus disease 2019 (COVID-19). Methods: To determine the analytical and clinical diagnostic performances of the direct detection assays, we compared 6 direct molecular detection assays, including two loop-mediated isothermal amplification (LAMP) assays and one lateral flow antigen assay, against the reference extraction-based RT-PCR assay using 183 respiratory samples (87 nasopharyngeal swabs, 51 saliva samples, and 45 sputum samples). Results: Analytical sensitivity analysis showed that the direct RT-PCR assay of Toyobo exhibited the lowest LOD of 1,000 copies/mL. Compared with the 80 positive and 103 negative samples based on the reference assay, the Toyobo assay had the highest positive percent agreement (PPA) of 96.3%, followed by the two direct RT-PCR assays of Takara and Shimadzu and one LAMP assay of Eiken (86.3-87.5%). The Fujirebio antigen assay had the lowest PPA of 44.7% among the assays tested. The negative percent agreement of these direct detection assays was 100%, except for the Eiken assay (96.3%). Conclusions: Large differences in PPA existed among the direct detection tests. Laboratories need to take these characteristics into consideration before implementing these assays.

Evaluation of Non-Invasive Gargle Lavage Sampling for the Detection of SARS-CoV-2 Using rRT-PCR or Antigen Assay.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused considerable disruption worldwide. For efficient SARS-CoV-2 detection, new methods of rapid, non-invasive sampling are needed. This study aimed to investigate the stability of SARS-CoV-2 in a novel medium for gargle-lavage (GL) self-sampling and to compare the performance of SARS-CoV-2 detection in paired self-collected GL and clinician-obtained nasopharyngeal swab (NPS) samples. The stability study for SARS-CoV-2 preservation in a novel medium was performed over 14 days (4 °C, 24-27 °C, and 37 °C). In total, 494 paired GL and NPS samples were obtained at the University Hospital in Olomouc in April 2021. SARS-CoV-2 detection in paired samples was performed with a SARS-CoV-2 Nucleic Acid Detection Kit (Zybio, Chongqing Municipality, Chongqing, China), an Elecsys® SARS-CoV-2 Antigen assay (Roche Diagnostics, Mannheim, Germany), and a SARS-CoV-2 Antigen ELISA (EUROIMMUN, Lübeck, Germany). The stability study demonstrated excellent SARS-CoV-2 preservation in the novel medium for 14 days. SARS-CoV-2 was detected in 55.7% of NPS samples and 55.7% of GL samples using rRT-PCR, with an overall agreement of 91.9%. The positive percent agreement (PPA) of the rRT-PCR in the GL samples was 92.7%, and the negative percent agreement (NPA) was 90.9%, compared with the NPS samples. The PPA of the rRT-PCR in the NPS and GL samples was 93.2% when all positive tests were used as the reference standard. Both antigen detection assays showed poor sensitivity compared to rRT-PCR (33.2% and 36.0%). rRT-PCR SARS-CoV-2 detection in self-collected GL samples had a similar PPA and NPA to that of NPSs. GL self-sampling offers a suitable and more comfortable alternative for SARS-CoV-2 detection.

SARS-CoV-2 RNA and N Antigen Quantification via Wastewater at the Campus Level, Building Cluster Level, and Individual-Building Level

Monitoring wastewater for SARS-CoV-2 from populations smaller than those served by wastewater treatment plants may help identify small spatial areas (subsewersheds) where COVID-19 infections are present. We sampled wastewater from three nested locations with different sized populations within the same sewer network at a university campus and quantified SARS-CoV-2 RNA using reverse transcriptase droplet digital polymerase chain reaction (PCR). SARS-CoV-2 RNA concentrations and/or concentrations normalized by PMMoV were positively associated with laboratory-confirmed COVID-19 cases for both the sewershed level and the subsewershed level. We also used an antigen-based assay to detect the nucleocapsid (N) antigen from SARS-CoV-2 in wastewater samples at the sewershed level. The N antigen was regularly detected at the sewershed level, but the results were not associated with either laboratory-confirmed COVID-19 cases or SARS-CoV-2 RNA concentrations. The results of this study indicate that wastewater monitoring based on quantification of SARS-CoV-2 RNA using PCR-based methods is associated with COVID-19 cases at multiple geographic scales within the subsewershed level and can serve to aid the public health response.

Performance of the Sofia SARS-CoV-2 Rapid Antigen Test in Symptomatic and Asymptomatic Pediatric Patients.

The sensitivity and specificity of SARS-CoV-2 antigen tests have not been widely assessed in children. We evaluated children presenting to outpatient care with Quidel Sofia SARS-CoV-2 antigen test (Sofia-Ag-RDT) compared against Cepheid Xpert Xpress SARS-CoV-2/Flu/RSV reverse transcriptase-polymerase chain reaction test from November 2020 to April 2021. Sofia-Ag-RDT had the highest sensitivity in symptomatic (82%; 95% confidence interval, 68%-91%) children.

Clinical Evaluation of BD Veritor SARS-CoV-2 and Flu A+B Assay for Point-Of-Care System.

Differential diagnosis of COVID-19 and/or influenza (flu) at point of care is critical for efficient patient management and treatment of both these diseases. The study presented here characterizes the BD Veritor System for Rapid Detection of SARS-CoV-2 and Flu A+B ("Veritor SARS-CoV-2/Flu") triplex assay. The performance for SARS-CoV-2 detection was determined using 298 specimens from patients reporting COVID-19 symptoms within 7 days from symptom onset (DSO) in comparison with the Lyra SARS-CoV-2 RT-PCR (reverse transcriptase PCR) assay ("Lyra SARS-CoV-2") as the reference. The performance for flu A and flu B detection was determined using 75 influenza-positive and 40 influenza-negative retrospective specimens in comparison with the previously FDA-cleared BD Veritor System for Rapid Detection of Flu A+B assay ("Veritor Flu") as the reference. The Veritor SARS-CoV-2/Flu assay met the FDA EUA acceptance criteria (86.7%; 95% confidence interval [95% CI]: 75.8 to 93.1) for SARS-CoV-2 testing compared to Lyra SARS-CoV-2. The Veritor SARS-CoV-2/Flu assay also demonstrated 100% agreement with the Veritor Flu for Flu A+B assay. For flu A detection, the lower bound of the 95% CI was 91.2%; for flu B detection, the lower bound was 90.0%. The dual detection capability of Veritor SARS-CoV-2/Flu for the etiologic agents causing COVID-19 and flu will allow efficient differentiation between the two illnesses, inform disease management, and facilitate optimal treatment. IMPORTANCE COVID-19 and flu are two respiratory illnesses which share similar clinical symptoms. The BD Veritor SARS-CoV-2/Flu assay has high sensitivity and specificity for detecting the SARS-CoV-2 and influenza A/B, the two etiologic agents causing COVID-19 and flu, respectively. This dual detection capability is critical when overlap occurs between the COVID-19 pandemic and the flu season. This triplex assay will allow efficient differentiation between the two respiratory illnesses and support a point-of-care physician diagnosis to facilitate the proper treatment and disease management for patients exhibiting overlapping symptoms.

A method comparison study of the high throughput automated HISCL® SARS-CoV-2 antigen assay using nasopharyngeal swab samples from symptomatic and asymptomatic subjects against conventional RT-PCR.

Our study aim was to evaluate the performance of the automated Sysmex HISCL® severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen assay against reverse-transcription polymerase chain reaction (RT-PCR). We tested 277 remnant frozen nasopharyngeal swab samples, stored in universal transport medium (UTM), yielding a sensitivity of 94.9% against historical RT-PCR results with cycle threshold (Ct ) < 30, and a sensitivity of 76.7% for Ct < 35, and specificity of 100% (all Ct values) confirming compatibility of UTM-diluted samples with the assay system. Thereafter, we prospectively collected 141 nasopharyngeal swab samples in UTM from healthcare workers and 1369 paired swabs (400 UTM; 969 dry) from individuals at a public health testing center, with the first swab (UTM) reserved for RT-PCR, yielding a positivity rate of 4.6%. HISCL assay performance using UTM swabs was superior to dry swabs, with a sensitivity of 100% (95% confidence interval [CI] 71.5%-100%) at Ct < 30 versus 92.3% (95%CI 81.5%-97.9%), and a specificity of 99.3% (95% CI 98.1-99.89) against 83.3% (95%CI 80.7%-85.6%). We conclude that this antigen assay is suitable for high throughput facilities where the primary indication for testing is to rule out infection with low RT-PCR Ct values (proxy for high viral loads) to curb viral spread.

Performance Assessment of the LIAISON® SARS-CoV-2 Antigen Assay On Nasopharyngeal Swabs

The SARS-CoV-2 pandemic is ongoing worldwide, causing prolonged pressure on molecular diagnostics. Viral antigen (Ag) assays have several advantages, ranging from lower cost to shorter turnaround time to detection. Given the rare occurrence of low-load viremia, antigen assays for SARS-CoV-2 have focused on nasopharyngeal swab and saliva as biological matrices, but their effectiveness must be validated. We assayed here the performances of the novel quantitative Liaison® SARS-CoV-2 Ag assay on 119 nasopharyngeal swabs and obtained results were compared with Hologic Panther and Abbott m2000 RT-qPCR. The Ag assay demonstrated a good correlation with viral load, shorter turnaround time, and favorable economics. The best performance was obtained in the acute phase of disease.

Evaluation of a rapid antigen detection test (Panbio™ COVID-19 Ag Rapid Test Device) as a point-of-care diagnostic tool for COVID-19 in a pediatric emergency department.

We evaluated the Panbio™ COVID-19 Ag Rapid Test Device as a point-of-care diagnostic tool for COVID-19 in 357 patients at a pediatric emergency department. Thirty-four patients tested positive by reverse transcription polymerase chain reaction, of which 24 were positive by the antigen assay. The sensitivity and specificity of the assay were 70.5% and 100%, respectively.

Comparison of Allplex™ SARS-CoV-2 Assay, Easy SARS-CoV-2 WE and Lumipulse quantitative SARS-CoV-2 antigen test performance using automated systems for the diagnosis of COVID-19.

Diagnostic methods based on SARS-CoV-2 antigen detection are a promising alternative to SARS-CoV-2 RNA amplification. We evaluated the automated chemiluminescence-based Lumipulse® G SARS-CoV-2 Ag assay as compared to real time assays (combined results from RT-PCR Allplex™ SARS-CoV-2 assay and Easy SARS-CoV-2 WE kit) on 513 nasopharyngeal swabs (NPS). Among these, 53.6% resulted positive to RT-PCR, considered as the reference test. Compared to the reference test, overall sensitivity and specificity of Lumipulse® G SARS-CoV-2 Ag assay were 84.0%, and 89.1%, respectively, and overall agreement between the antigen and molecular assays was substantial (κ = 0.727). When stratifying samples into groups based on ranges of RT-PCR cycle threshold (Ct), the antigen test sensitivity was >95% for samples with Ct <30. Linear regression analysis showed strong and highly significant correlation between the Lumipulse Ag concentrations and the RT-PCR Ct values (RdRp gene), irrespective of whether the Ct values from molecular test were combined in a unique regression analysis or analysed separately. Overall, chemiluminescence-based antigen assay may be reliably applied to NPS samples to identify individuals with high viral loads, more likely to transmit the virus.

Performance of six rapid diagnostic tests for SARS-CoV-2 antigen detection and implications for practical use.

BACKGROUND: Direct detection of SARS-CoV-2 viral proteins in nasopharyngeal swabs using lateral flow immunoassays is a simple, fast and cheap approach to diagnose the infection. AIMS AND METHODS: The performance of 6 SARS-CoV-2 antigen rapid diagnostic tests has been assessed in 634 hospitalized patients or outpatients including 297 patients found to be positive for SARS-CoV-2 RNA by means of RT-PCR and 337 patients presumed to be SARS-CoV-2 RNA-negative. RESULTS: The specificity of SARS-CoV-2 RDTs was generally high (398.5%). One assay had a lower specificity of 93.2%. The overall sensitivity of the 6 RDTs was variable, from 32.3% to 61.7%. Sensitivity correlated with the delay of sampling after the onset of symptoms and the viral load estimated by the Ct value in RT-PCR. Four out of 6 RDTs tested achieved sensitivities 380% when clinical specimens were collected during the first 3 days following symptom onset or with a Ct value ≤25. CONCLUSIONS: The present study shows that SARS-CoV-2 antigen can be easily and reliably detected by RDTs. These tests are easy and rapid to perform. However, the specificity and sensitivity of COVID-19 antigen RDTs may widely vary across different tests and must therefore be carefully evaluated before releasing these assays for realworld applications.

Reduced Relative Sensitivity of the Elecsys SARS-CoV-2 Antigen Assay in Saliva Compared to Nasopharyngeal Swabs.

Early identification and isolation of SARS-CoV-2-infected individuals is central to contain the COVID-19 pandemic. Nasopharyngeal swabs (NPS) serve as a specimen for detection by RT-PCR and rapid antigen screening tests. Saliva has been confirmed as a reliable alternative specimen for RT-PCR and has been shown to be valuable for diagnosing children and in repetitive mass testing due to its non-invasive collection. Combining the advantages of saliva with those of antigen tests would be highly attractive to further increase test capacities. Here, we evaluated the performance of the Elecsys SARS-CoV-2 Antigen assay (Roche) in RT-PCR-positive paired NPS and saliva samples (N = 87) and unpaired NPS (N = 100) with confirmed SARS-CoV-2 infection (Roche cobas SARS-CoV-2 IVD test). We observed a high positive percent agreement (PPA) of the antigen assay with RT-PCR in NPS, reaching 87.2% across the entire cohort, whereas the overall PPA for saliva was insufficient (40.2%). At Ct values ≤ 28, PPA were 100% and 91.2% for NPS and saliva, respectively. At lower viral loads, the sensitivity loss of the antigen assay in saliva was striking. At Ct values ≤ 35, the PPA for NPS remained satisfactory (91.5%), whereas the PPA for saliva dropped to 46.6%. In conclusion, saliva cannot be recommended as a reliable alternative to NPS for testing with the Elecsys Anti-SARS-CoV-2 Antigen assay. As saliva is successfully used broadly in combination with RT-PCR testing, it is critical to create awareness that suitability for RT-PCR cannot be translated to implementation in antigen assays without thorough evaluation of each individual test system.