Five Antigen Tests for SARS-CoV-2: Virus Viability Matters

Antigen testing for SARS-CoV-2 (AGT) is generally considered inferior to RT-PCR testing in terms of sensitivity. However, little is known about the infectiousness of RT-PCR positive patients who pass undetected by AGT. In a screening setting for mildly symptomatic or asymptomatic patients with high COVID-19 prevalence (30–40%), 1141 patients were tested using one of five AGTs and RT-PCR. Where the results differed, virus viability in the samples was tested on cell culture (CV-1 cells). The test battery included AGTs by JOYSBIO, Assure Tech, SD Biosensor, VivaChek Biotech and NDFOS. Sensitivities of the ATGs compared to RT-PCR ranged from 42% to 76%. The best test yielded a 76% sensitivity, 97% specificity, 92% positive, and 89% negative predictive values, respectively. However, in the best performing ATG tests, almost 90% of samples with “false negative” AGT results contained no viable virus. Corrected on the virus viability, sensitivities grew to 81%–97% and, with one exception, the tests yielded high specificities >96%. Performance characteristics of the best test after adjustment were 96% sensitivity, 97% specificity, 92% positive, and 99% negative predictive values (high prevalence population). We, therefore, believe that virus viability should be considered when assessing the AGT performance. Also, our results indicate that a well-performing antigen test could in a high-prevalence setting serve as an excellent tool for identifying patients shedding viable virus. We also propose that the high proportion of RT-PCR-positive samples containing no viable virus in the group of “false negatives” of the antigen test should be further investigated with the aim of possibly preventing needless isolation of such patients.

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Detection of SARS-CoV-2 infection by rapid antigen test in comparison with RT-PCR in a public setting

10.1101/2021.01.22.21250042 ◽

2021 ◽

Cited By ~ 1

Author(s):

Kathrine Kronberg Jakobsen ◽

Jakob Schmidt Jensen ◽

Tobias Todsen ◽

Freddy Lippert ◽

Cyril Jean-Marie Martel ◽

...

Keyword(s):

False Negative ◽

Pcr Analysis ◽

Nasopharyngeal Swab ◽

Test Results ◽

Antigen Test ◽

Rt Pcr ◽

Predictive Values ◽

Public Setting ◽

Antigen Tests ◽

Sensitivity Specificity

AbstractBackgroundRapid and accurate detection of SARS-CoV-2 infection is essential in limiting the spread of infection during the ongoing COVID-19 pandemic. The aim of this study was to determine the accuracy of the STANDARD Q COVID-19 Ag test (SD BIOSENSOR) by comparison with RT-PCR in a public setting.MethodIndividuals aged 18 years or older who had booked an appointment for a RT-PCR test on December 26-31, 2020 at a public test center in Copenhagen, Denmark, were invited to participate. An oropharyngeal swab was collected for RT-PCR analysis, immediately followed by a nasopharyngeal swab examined by the STANDARD Q COVID-19 Ag test (SD BIOSENSOR). Sensitivity, specificity, positive and negative predictive values of the antigen test were calculated with test results from RT-PCR as reference.ResultsOverall, 4697 individuals were included (female n=2456, 53.3%; mean age: 44.7 years, SD: 16.9 years); 196 individuals were tested twice or more. Among 4811 paired conclusive test results from the RT-PCR and antigen tests, 221 (4.6%) RT-PCR tests were positive. The overall sensitivity and specificity of the antigen test were 69.7% and 99.5%, the positive and negative predictive values were 87.0% and 98.5%. Ct values were significantly higher among individuals with false negative antigen tests compared to true positives.ConclusionThe sensitivity, specificity, and predictive values found indicate that the STANDARD Q COVID-19 Ag is a good supplement to RT-PCR testing.

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Diagnostic performance of a novel digital immunoassay (RapidTesta SARS-CoV-2): a prospective observational study with 1,127 nasopharyngeal samples

10.1101/2021.07.26.21261162 ◽

2021 ◽

Author(s):

Hiromichi Suzuki ◽

Yusaku Akashi ◽

Atsuo Ueda ◽

Yoshihiko Kiyasu ◽

Yuto Takeuchi ◽

...

Keyword(s):

Diagnostic Performance ◽

Prospective Observational Study ◽

Test Results ◽

Antigen Test ◽

Rt Pcr ◽

Asymptomatic Patients ◽

Pcr Method ◽

Antigen Tests ◽

Positive Line ◽

Test Cassette

Introduction: Digital immunoassays are generally regarded as superior tests for the detection of infectious disease pathogens, but there have been insufficient data concerning SARS-CoV-2 immunoassays. Methods: We prospectively evaluated a novel digital immunoassay (RapidTesta SARS-CoV-2). Two nasopharyngeal samples were simultaneously collected for antigen tests and RT-PCR. Real-time RT-PCR for SARS-CoV-2, using a method developed by the National Institute of Infectious Diseases, Japan, served as the reference RT-PCR method. Results: During the study period, 1,127 nasopharyngeal samples (symptomatic patients: 802, asymptomatic patients: 325) were evaluated. For digital immunoassay antigen tests, the sensitivity was 78.3% (95% CI: 67.3%-87.1%) and the specificity was 97.6% (95% CI: 96.5%-98.5%). When technicians visually analyzed the antigen test results, the sensitivity was 71.6% (95% CI: 59.9%-81.5%) and the specificity was 99.2% (95% CI: 98.5%-99.7%). Among symptomatic patients, the sensitivity was 89.4% (95% CI; 76.9%-96.5%) with digital immunoassay antigen tests, and 85.1% (95% CI; 71.7%-93.8%) with visually analyzed the antigen test, respectively. Conclusions: The findings indicated that RapidTesta SARS-CoV-2 analysis with the DIA device had sufficient analytical performance for the detection of SARS-CoV-2 in nasopharyngeal samples. When positive DIA results are recorded without a visually recognizable red line at the positive line location on the test cassette, additional RT-PCR evaluation should be performed.

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At-home self-testing of teachers with a SARS-CoV-2 rapid antigen test to reduce potential transmissions in schools

10.1101/2020.12.04.20243410 ◽

2020 ◽

Author(s):

Sebastian Hoehl ◽

Barbara Schenk ◽

Olga Rudych ◽

Stephan Göttig ◽

Ivo Foppa ◽

...

Keyword(s):

False Positive ◽

High Frequency ◽

False Negative ◽

Study Participant ◽

Lower Sensitivity ◽

Antigen Test ◽

Rt Pcr ◽

Antigen Tests ◽

Positive Results ◽

At Home

AbstractBackgroundRapid antigen tests for SARS-CoV-2 became available recently, offering an opportunity to vastly increase testing capacities. Antigen tests offer lower sensitivity than the gold standard, RT-PCR, but rapid sample-to-answer time. High-frequency testing with an antigen test may offset the lower sensitivity, and testing can be done with at-home collection of samples, offering potential benefit in screening efforts. In this study, we set out to evaluate the practical application of self-performed high-frequency antigen test in a school setting.MethodA total of 711 teachers from 86 schools were enrolled in a seven-week study. After instruction, participants tested themselves every 48 hours at home with a rapid antigen test for SARS-CoV-2 (target: nucleocapsid protein) in a self-collected anterior nasal swab. Positive results in the antigen test were confirmed via RT-PCR from the same sample that had been determined to be positive by the study participant. A questionnaire was given to all participants to evaluate whether the test failed to detect infection.Findings10 836 tests from 602 teachers were recorded and analyzed. A total of five confirmed cases of viral shedding of SARS-CoV-2 was detected by use of the antigen test. One study participant with a SARS-CoV-2 infection was presymptomatic and four were mildly symptomatic at the time of the antigen test. Sixteen false positive antigen tests (0.15% of all tests) were reported, predominantly when the local incidence in the general population was low. In four cases, the study participant reported that a PCR had detected a SARS-CoV-2 infection, but the antigen test was negative, indicating a false negative result.InterpretationHigh-frequency, self-performed rapid antigen tests can detect individuals with a SARS-CoV-2 infection, and therefore potentially reduce transmissions. Testing may be most beneficial when applied during high local incidence of SARS-CoV-2 infections and when mild or atypical symptoms are present. To avoid a high rate of false positive results, a test with optimized specificity should be used.FundingThe study was commissioned and funded by the Hessian Ministry of Education and the Hessian Ministry of Integration and Social Affairs.

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Diagnostic accuracy of rapid antigen tests in asymptomatic and presymptomatic close contacts of individuals with confirmed SARS-CoV-2 infection: cross sectional study

BMJ ◽

10.1136/bmj.n1676 ◽

2021 ◽

pp. n1676

Author(s):

Ewoud Schuit ◽

Irene K Veldhuijzen ◽

Roderick P Venekamp ◽

Wouter van den Bijllaardt ◽

Suzan D Pas ◽

...

Keyword(s):

Viral Load ◽

Cross Sectional Study ◽

Antigen Test ◽

Sectional Study ◽

Rt Pcr ◽

Cross Sectional ◽

Predictive Values ◽

Test Sensitivity ◽

Antigen Tests ◽

Close Contacts

Abstract Objective To assess the diagnostic test accuracy of two rapid antigen tests in asymptomatic and presymptomatic close contacts of people with SARS-CoV-2 infection on day 5 after exposure. Design Prospective cross sectional study. Setting Four public health service covid-19 test sites in the Netherlands. Participants 4274 consecutively included close contacts (identified through test-and-trace programme or contact tracing app) aged 16 years or older and asymptomatic for covid-19 when requesting a test. Main outcome measures Sensitivity, specificity, and positive and negative predictive values of Veritor System (Beckton Dickinson) and Biosensor (Roche Diagnostics) rapid antigen tests, with reverse-transcriptase polymerase chain reaction (RT-PCR) testing as reference standard. The viral load cut-off above which 95% of people with a positive RT-PCR test result were virus culture positive was used as a proxy of infectiousness. Results Of 2678 participants tested with Veritor, 233 (8.7%) had a RT-PCR confirmed SARS-CoV-2 infection of whom 149 were also detected by the rapid antigen test (sensitivity 63.9%, 95% confidence interval 57.4% to 70.1%). Of 1596 participants tested with Biosensor, 132 (8.3%) had a RT-PCR confirmed SARS-CoV-2 infection of whom 83 were detected by the rapid antigen test (sensitivity 62.9%, 54.0% to 71.1%). In those who were still asymptomatic at the time of sampling, sensitivity was 58.7% (51.1% to 66.0%) for Veritor (n=2317) and 59.4% (49.2% to 69.1%) for Biosensor (n=1414), and in those who developed symptoms were 84.2% (68.7% to 94.0%; n=219) for Veritor and 73.3% (54.1% to 87.7%; n=158) for Biosensor. When a viral load cut-off was applied for infectiouness (≥5.2 log10 SARS-CoV-2 E gene copies/mL), the overall sensitivity was 90.1% (84.2% to 94.4%) for Veritor and 86.8% (78.1% to 93.0%) for Biosensor, and 88.1% (80.5% to 93.5%) for Veritor and 85.1% (74.3% to 92.6%) for Biosensor, among those who remained asymptomatic throughout. Specificities were >99%, and positive and negative predictive values were >90% and >95%, for both rapid antigen tests in all analyses. Conclusions The sensitivities of both rapid antigen tests in asymptomatic and presymptomatic close contacts tested on day 5 onwards after close contact with an index case were more than 60%, increasing to more than 85% after a viral load cut-off was applied as a proxy for infectiousness.

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The dark side of SARS-CoV-2 rapid antigen testing: screening asymptomatic patients

10.1101/2021.04.24.21256040 ◽

2021 ◽

Author(s):

Giorgia Caruana ◽

Laure-Line Lebrun ◽

Oriane Aebischer ◽

Onya Opota ◽

Luis Urbano ◽

...

Keyword(s):

Hospital Admissions ◽

Screening Method ◽

Dark Side ◽

Pcr Analysis ◽

Rt Pcr ◽

Asymptomatic Patients ◽

Antigen Tests ◽

Outpatient Settings ◽

Antigen Testing

AbstractMost of the reports describing SARS-CoV-2 rapid antigen tests (RATs) performances derive from COVID-19 symptomatic subjects in outpatient settings during periods of highest incidence of infections and high rates of hospital admissions. Here we investigated the role of RATs in an Emergency Department, as a screening tool before admission for COVID-19 asymptomatic patients. Each patient was screened with two simultaneous nasopharyngeal swabs: one immediately analyzed at the bedside using RAT and the other sent to the laboratory for RT-PCR analysis. A total of 116 patients were screened at hospital admission in a 250-bed community hospital in Morges (EHC), Switzerland. With a disease prevalence of 6% based on RT-PCR results, RAT detected only two out of seven RT-PCR positive patients (sensitivity 28.6%) and delivered two false positive results (specificity 98.2%), thus resulting not fiable enough to be used as a screening method in this clinical scenario.

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Clinical Evaluation of Sofia Rapid Antigen Assay for Detection of Severe Acute Respiratory Syndrome Coronavirus 2 among Emergency Department to Hospital Admissions

Infection Control and Hospital Epidemiology ◽

10.1017/ice.2021.281 ◽

2021 ◽

pp. 1-22

Author(s):

Richard D. Smith ◽

J. Kristie Johnson ◽

Colleen Clay ◽

Leo Girio-Herrera ◽

Diane Stevens ◽

...

Keyword(s):

Emergency Department ◽

Hospital Admissions ◽

False Negative ◽

Symptom Assessment ◽

Rt Pcr ◽

Cross Sectional ◽

Assay Sensitivity ◽

Predictive Values ◽

Asymptomatic Patients ◽

Antigen Assay

Abstract Objective To determine the utility of the Sofia® SARS rapid antigen fluorescent immunoassay (FIA) to guide hospital bed placement of patients being admitted through the emergency department (ED). Design Cross-sectional analysis of a clinical quality improvement study. Setting Two community hospitals in Maryland. From 9/21/2020 to 12/3/2020, 2887 patients simultaneously received the Sofia® SARS rapid antigen FIA and SARS-CoV-2 RT-PCR assays on admission through the ED. Methods Rapid antigen results and symptom assessment guided initial patient placement while confirmatory RT-PCR was pending. The sensitivity, specificity, positive and negative predictive values of the rapid antigen assay were calculated relative to RT-PCR, overall and separately for symptomatic and asymptomatic patients. Assay sensitivity was compared to RT-PCR cycle threshold (Ct) values. Assay turnaround times were compared. Clinical characteristics of RT-PCR positive patients and potential exposures from false-negative antigen assays were evaluated. Results Overall agreement, sensitivity, and specificity for all patients was 97.9%, 76.6% (95% confidence interval (CI): 71%, 82%), and 99.7% (95% CI: 99%, 100%), respectively. No differences in performance were seen between asymptomatic and symptomatic individuals. As RT-PCR Ct increased, sensitivity of the antigen assay decreased. Mean turnaround time for the antigen assay and RT-PCR was 1.2 (95% CI: 1.0, 1.3) and 20.1 (95% CI: 18.9, 40.3) hours, respectively (p<0.001). No transmission from antigen-negative/RT-PCR-positive patients was identified. Conclusions While not a replacement for RT-PCR for detection of all SARS-CoV-2 infections, the Sofia® SARS antigen FIA has clinical utility for potential initial timely patient placement.

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Implementing SARS-CoV-2 Rapid Antigen Testing in the Emergency Ward of a Swiss University Hospital: The INCREASE Study

Microorganisms ◽

10.3390/microorganisms9040798 ◽

2021 ◽

Vol 9 (4) ◽

pp. 798

Author(s):

Giorgia Caruana ◽

Antony Croxatto ◽

Eleftheria Kampouri ◽

Antonios Kritikos ◽

Onya Opota ◽

...

Keyword(s):

Immunoglobulin A ◽

University Hospital ◽

Lower Sensitivity ◽

Clinical Settings ◽

Rt Pcr ◽

Emergency Ward ◽

Viral Loads ◽

Asymptomatic Patients ◽

Asymptomatic Subjects ◽

Antigen Testing

Following the Swiss Federal Office of Public Health (FOPH) authorization of the rapid antigen test (RAT), we implemented the use of the RAT in the emergency ward of our university hospital for patients’ cohorting. RAT triaging in association with RT-PCR allowed us to promptly isolate positive patients and save resources. Among 532 patients, overall sensitivities were 48.3% for Exdia and 41.2% for Standard Q®, PanbioTM and BD Veritor™. All RATs exhibited specificity above 99%. Sensitivity increased to 74.6%, 66.2%, 66.2% and 64.8% for Exdia, Standard Q®, PanbioTM and BD Veritor™, respectively, for viral loads above 105 copies/mL, to 100%, 97.8%, 96.6% and 95.6% for viral loads above 106 copies/mL and 100% for viral loads above 107 copies/mL. Sensitivity was significantly higher for patients with symptoms onset within four days (74.3%, 69.2%, 69.2% and 64%, respectively) versus patients with the evolution of symptoms longer than four days (36.8%, 21.1%, 21.1% and 23.7%, respectively). Among COVID-19 asymptomatic patients, sensitivity was 33%. All Immunoglobulin-A-positive patients resulted negative for RAT. The RAT might represent a useful resource in selected clinical settings as a complementary tool in RT-PCR for rapid patient triaging, but the lower sensitivity, especially in late presenters and COVID-19 asymptomatic subjects, must be taken into account.

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Performance of Unobserved Self-Collected Nasal Swabs for Detection of SARS-CoV-2 by RT-PCR Utilizing a Remote Specimen Collection Strategy

Open Forum Infectious Diseases ◽

10.1093/ofid/ofab039 ◽

2021 ◽

Author(s):

Ron M Kagan ◽

Amy A Rogers ◽

Gwynngelle A Borillo ◽

Nigel J Clarke ◽

Elizabeth M Marlowe

Keyword(s):

Return To Work ◽

Screening Program ◽

False Negative ◽

N Gene ◽

Rt Pcr ◽

Pooled Testing ◽

Specimen Collection ◽

Asymptomatic Patients ◽

Nasal Swabs ◽

The Impact

Abstract Background The use of a remote specimen collection strategy employing a kit designed for unobserved self-collection for SARS-CoV-2 RT-PCR can decrease the use of PPE and exposure risk. To assess the impact of unobserved specimen self-collection on test performance, we examined results from a SARS-CoV-2 qualitative RT-PCR test for self-collected specimens from participants in a return-to-work screening program and assessed the impact of a pooled testing strategy in this cohort. Methods Self-collected anterior nasal swabs from employee return to work programs were tested using the Quest Diagnostics SARS-CoV-2 RT-PCR EUA. The Ct values for the N1 and N3 N-gene targets and a human RNase P (RP) gene control target were tabulated. For comparison, we utilized Ct values from a cohort of HCP-collected specimens from patients with and without COVID-19 symptoms. Results Among 47,923 participants, 1.8% were positive. RP failed to amplify for 13/115,435 (0.011%) specimens. The median (IQR) Cts were 32.7 (25.0-35.7) for N1 and 31.3 (23.8-34.2) for N3. Median Ct values in the self-collected cohort were significantly higher than those of symptomatic, but not asymptomatic patients. Based on Ct values, pooled testing with 4 specimens would have yielded inconclusive results in 67/1,268 (5.2%) specimens but only a single false-negative result. Conclusions Unobserved self-collection of nasal swabs provides adequate sampling for SARS-CoV-2 RT-PCR testing. These findings alleviate concerns of increased false negatives in this context. Specimen pooling could be used for this population as the likelihood of false negative results is very low due when using a sensitive, dual-target methodology.

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Incorporating false negative tests in epidemiological models for SARS-CoV-2 transmission and reconciling with seroprevalence estimates

Scientific Reports ◽

10.1038/s41598-021-89127-1 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Rupam Bhattacharyya ◽

Ritoban Kundu ◽

Ritwik Bhaduri ◽

Debashree Ray ◽

Lauren J. Beesley ◽

...

Keyword(s):

False Negative ◽

Population Based ◽

Training Data ◽

Epidemiological Models ◽

Rt Pcr ◽

Antibody Prevalence ◽

Igg Antibody ◽

False Negatives ◽

Seir Model ◽

Study Population

AbstractSusceptible-Exposed-Infected-Removed (SEIR)-type epidemiologic models, modeling unascertained infections latently, can predict unreported cases and deaths assuming perfect testing. We apply a method we developed to account for the high false negative rates of diagnostic RT-PCR tests for detecting an active SARS-CoV-2 infection in a classic SEIR model. The number of unascertained cases and false negatives being unobservable in a real study, population-based serosurveys can help validate model projections. Applying our method to training data from Delhi, India, during March 15–June 30, 2020, we estimate the underreporting factor for cases at 34–53 (deaths: 8–13) on July 10, 2020, largely consistent with the findings of the first round of serosurveys for Delhi (done during June 27–July 10, 2020) with an estimated 22.86% IgG antibody prevalence, yielding estimated underreporting factors of 30–42 for cases. Together, these imply approximately 96–98% cases in Delhi remained unreported (July 10, 2020). Updated calculations using training data during March 15-December 31, 2020 yield estimated underreporting factor for cases at 13–22 (deaths: 3–7) on January 23, 2021, which are again consistent with the latest (fifth) round of serosurveys for Delhi (done during January 15–23, 2021) with an estimated 56.13% IgG antibody prevalence, yielding an estimated range for the underreporting factor for cases at 17–21. Together, these updated estimates imply approximately 92–96% cases in Delhi remained unreported (January 23, 2021). Such model-based estimates, updated with latest data, provide a viable alternative to repeated resource-intensive serosurveys for tracking unreported cases and deaths and gauging the true extent of the pandemic.

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Role of Covid Antigen in the Diagnosis of Covid Positive in Obstetric Patients

10.53350/pjmhs2115103356 ◽

2021 ◽

Vol 15 (10) ◽

pp. 3356-3358

Author(s):

Ambreen Fatima ◽

Nidda Yaseen ◽

Amna Fareed ◽

Kashif Ali Samin ◽

Shumaela Kanwal ◽

...

Keyword(s):

Nucleic Acid ◽

Early Detection ◽

Negative Predictive Value ◽

Predictive Value ◽

False Negative ◽

Nucleic Acid Amplification ◽

Antigen Test ◽

Rt Pcr ◽

Cross Sectional ◽

Specificity And Sensitivity

Background and Aim: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapid emergence postured significant challenges on the health system in recent years. The early detection of cases is thought to be critical in preventing this pandemic by coronavirus disease (COVID-19), especially important in the obstetrical population due to theirs numerous interactions with another parturient when hospitalized for delivery. Therefore, the present study aimed to assess the COVID antigen test performance in COVID-positive obstetrics patients. Materials and Methods: This cross-sectional study was conducted on 1296 Covid-19 asymptomatic women admitted to the Obstetrics and Gynaecology Department of Muhammad Teaching Hospital & Medical College, Peshawar and Fauji Foundation Hospital, Rawalpindi for the duration of six months from February 2021 to July 2021. Antigen-based test rapid diagnostic test (RDT) was used for screening out COVID-19 positive obstetrics patients or women through nasopharyngeal swabs. Women with negative rapid antigen test results were confirmed with RT-polymers chain reaction test of nucleic acid amplification tests (NAAT). Ethical approval and informed consent were taken from the hospital ethical committee and each individual respectively. All the known positive COVID-19 patients during admission were excluded. SPSS version 24 was used for data analysis. Results: The overall prevalence of rapid antigen-positive tested patients was 13.2% (171/1296). The prevalence of positive tested women through rapid antigen test, Nucleic Acid Amplification Test (NAAT), and RT-PCR were 27 (2.1%), 51 (3.9%), and 93 (7.2%) respectively. Of the total 1296 rapid antigen tests, 27 were positive, and the false-negative confirmed positive by NAAT was 144.Thus the sensitivity of the rapid antigen test was 15.8% and the negative predictive value was 93.7%. Of the total 298 Nucleic Acid Amplification Tested had sensitivity and negative predictive value of 89.6% and 99.06% respectively. RT-PCR was carried out on 972 patients, positive diagnosed cases were 36 while 15 were initially negative and were positive with the test was repeated. The sensitivity and negative predictive value was 71.45% and 95.8% respectively. Conclusion: Our study found that Ag-RDT plays a significant role in SARS-CoV-2 early detection in infected individuals, with high specificity and sensitivity to disease infectious stage, whether symptomatic or asymptomatic, and can be used as a decision supported tool. Early detection of COVID-19 status in women admitted for delivery could benefit neonatal protection care. Keywords: Covid-19; Rapid antigen test; RT-PCR test

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