scholarly journals Association between viral load and positivization time of a SARS-CoV-2 rapid antigen test in routine nasopharyngeal specimens

2021 ◽  
Author(s):  
Gian Luca Salvagno ◽  
Brandon Michael Henry ◽  
Simone De Nitto ◽  
Laura Pighi ◽  
Giuseppe Lippi
Keyword(s):  
Viral Load ◽  
Diagnostic Testing ◽  
Area Under The Curve ◽  
High Viral Load ◽  
Antigen Test ◽  
Potential Association ◽  
Antigen Tests ◽  
Antigen Testing ◽  
Spearman’S Correlation ◽  
Positive Results

Abstract Background: Rapid SARS-CoV-2 antigen tests are potentially useful tools for screening carriers with high viral load. This study was aimed to assess the potential association between viral load and positivization time of a manual SARS-CoV-2 commercial antigen test in routine nasopharyngeal specimens. Methods: In a sample of subjects undergoing routine diagnostic testing, SARS-CoV-2 positivity of nasopharyngeal samples was assayed with both molecular (Altona Diagnostics RealStar SARS-CoV-2 RT-PCR Kit) and antigenic (Roche SARS-CoV-2 Rapid Antigen Test) tests. Positivization time of rapid antigen test was correlated and compared with viral load expressed as mean of SARS-CoV-2 E/S genes cycle threshold (Ct) values.Results: The study sample consisted of 106 patients (median age 48 years, 55 women) with positive results of rapid SARS-CoV-2 antigen testing. A highly significant Spearman’s correlation was found between mean SARS-CoV-2 E/S genes Ct values and positivization time of manual antigen test (r= 0.70; p<0.001). The positivization time of rapid SARS-CoV-2 antigen test displayed an area under the curve of 0.82 (95%CI, 0.74-0.89) for predicting nasopharyngeal samples with high viral load (i.e., mean Ct <20). A positivization time cut-off of 32 sec had 94.9% sensitivity and 58.2% specificity for detecting specimens with high viral load. The overall agreement between mean Ct value <20 and positivization time <32 sec was 70.8%.Conclusions: Positivization time of rapid SARS-CoV-2 antigen tests may provide easy and rapid information on viral load, thus making this type of manual assay potentially suitable for quick and reliable detection and isolation of super-carries.

scholarly journals SARS-CoV-2 Antigen Tests Predict Infectivity Based on Viral Culture: Comparison of Antigen, PCR Viral Load, and Viral Culture Testing on a Large Sample Cohort

2021 ◽  
Author(s):  
James E Kirby ◽  
Stefan Riedel ◽  
Sanjucta Dutta ◽  
Ramy Arnaout ◽  
Annie Cheng ◽  
...  
Keyword(s):  
Viral Load ◽  
Diagnostic Testing ◽  
Lateral Flow ◽  
Nasopharyngeal Swab ◽  
Viral Culture ◽  
Culture Positivity ◽  
Antigen Tests ◽  
Relationship Of ◽  
The Relationship ◽  
Antigen Testing

The relationship of SARS-CoV-2 antigen testing results, viral load, and viral culture detection remains to be fully defined. Presumptively, viral culture can provide a surrogate measure for infectivity of sampled individuals, and thereby inform how and where to most appropriately deploy available diagnostic testing modalities. We therefore determined the relationship of antigen testing results from three lateral flow and one microfluidics assay to viral culture performed in parallel in 181 nasopharyngeal swab samples positive for SARS-CoV-2. Sample viral loads, determined by RT-qPCR, were distributed across the range of viral load values observed in our testing population. We found that antigen tests were predictive of viral culture positivity, with the LumiraDx method showing enhanced sensitivity (90%; 95% confidence interval (95% CI) 83-94%) compared with the BD Veritor (74%, 95% CI 65-81%), CareStart (74%, 95% CI 65-81%) and Oscar Corona (74%, 95% CI 65-82%) lateral flow antigen tests. Antigen and viral culture positivity were also highly correlated with sample viral load, with areas under the receiver?operator characteristic curves (ROCs) of 0.94-0.97 and 0.92, respectively. In particular, a viral load threshold of 100,000 copies/mL was 95% sensitive (95% CI, 90-98%) and 72% specific (95% CI, 60-81%) for predicting viral culture positivity. Taken together, the detection of SARS-CoV-2 antigen identified highly infectious individuals, some of whom may harbor 10,000-fold more virus in their samples than those with any detectable infectious virus. As such, our data support use of antigen testing in defining infectivity status at the time of sampling.

scholarly journals Evaluation and clinical implications of the time to a positive results of antigen testing for SARS-CoV-2

2021 ◽  
Author(s):  
Yusaku Akashi ◽  
Yoshihiko Kiyasu ◽  
Yuto Takeuchi ◽  
Daisuke Kato ◽  
Miwa Kuwahara ◽  
...  
Keyword(s):  
Clinical Utility ◽  
Clinical Implications ◽  
Antigen Test ◽  
Test Sensitivity ◽  
Reverse Transcription Pcr ◽  
Time Period ◽  
Antigen Tests ◽  
Respiratory Coronavirus ◽  
Antigen Testing ◽  
Positive Results

Antigen tests for severe acute respiratory coronavirus 2 sometimes show positive lines earlier than their specified read time, although the implication of getting the results at earlier time is not well understood. This study aimed to evaluate the clinical utility of an antigen test by evaluating the time period to get positive results and by comparing the test sensitivity with that of a digital immunoassay (DIA) test. We prospectively collected additional nasopharyngeal samples from patients who had already tested positive for SARS-CoV-2 by reverse transcription PCR. The additional swab was used for an antigen test, QuickNavi™-COVID19 Ag, and the time periods to get positive results were measured. The sensitivity of QuickNavi™-COVID19 Ag was also compared with that of a DIA. In 84 of 96 (87.5%) analyzed cases, the results of QuickNavi™-COVID19 Ag were positive. The time to obtain positive results was 15.0 seconds in median (inter quartile range: 12.0-33.3, range 11-736), and was extended in samples with higher cycle thresholds (Ct) (p<0.001). Positive lines appeared within a minute in 85.7% of cases and within 5 minutes in 96.4%. The sensitivities of QuickNavi™-COVID19 Ag and the DIA were 87.5% (95% confident interval [CI]: 79.2%-93.4%) and 88.6% (95%CI: 75.4%-96.2%), respectively. Their results were concordant in 90.9% of cases, with discrepancies present only in cases with Ct values >32. QuickNavi™-COVID19 Ag immediately showed positive results in most cases, and the time to a positive reaction may have indicated the viral load. In addition, the sensitivity of the test was comparable to the DIA.

scholarly journals Direct Comparison of SARS Co-V-2 Nasal RT- PCR and Rapid Antigen Test (BinaxNOWTM) at a Community Testing Site During an Omicron Surge

2022 ◽  
Author(s):  
John Schrom ◽  
Carina Marquez ◽  
Genay Pilarowski ◽  
Grace Wang ◽  
Anthea Mitchell ◽  
...  
Keyword(s):  
San Francisco ◽  
High Viral Load ◽  
Antigen Test ◽  
Rt Pcr ◽  
Repeat Testing ◽  
Single Antigen ◽  
Testing Site ◽  
Antigen Testing ◽  
Test Result ◽  
Community Site

In 731 persons seeking COVID-19 testing at a walk-up San Francisco community site in January 2022, simultaneous nasal rapid antigen testing (BinaxNOWTM) and RT-PCR testing was performed. There were 296 (40.5%) positive tests by RT-PCR; 97% of a random sample were the omicron variant. Sensitivity of a single antigen test was 95.2% (95% CI 92-98%); 82.1% (95% CI 77-87%) and 65.2% (95% CI 60-70%) for Ct threshold of < 30, < 35 and no threshold, respectively. A single BinaxNowTM rapid antigen test detected 95% of high viral load omicron cases from nasal specimens. As currently recommended, repeat testing should be done for high- risk persons with an initial negative antigen test result.

scholarly journals Performance characteristics of a rapid SARS-CoV-2 antigen detection assay at a public plaza testing site in San Francisco

2020 ◽  
Author(s):  
Genay Pilarowski ◽  
Paul Lebel ◽  
Sara Sunshine ◽  
Jamin Liu ◽  
Emily Crawford ◽  
...  
Keyword(s):  
Viral Load ◽  
San Francisco ◽  
High Viral Load ◽  
Performance Characteristics ◽  
Viral Rna ◽  
Antigen Test ◽  
Rt Pcr ◽  
Detection Assay ◽  
Community Transmission ◽  
Testing Site

ABSTRACTWe evaluated the performance of the Abbott BinaxNOW™ Covid-19 rapid antigen test to detect virus among persons, regardless of symptoms, at a public plaza site of ongoing community transmission. Titration with cultured clinical SARS-CoV-2 yielded a human observable threshold between 1.6×104-4.3×104 viral RNA copies (cycle threshold (Ct) of 30.3-28.8 in this assay). Among 878 subjects tested, 3% (26/878) were positive by RT-PCR, of which 15/26 had a Ct<30, indicating high viral load. 40% (6/15) of Ct<30 were asymptomatic. Using this Ct<30 threshold for Binax-CoV2 evaluation, the sensitivity of the Binax-CoV2 was 93.3% (14/15), 95% CI: 68.1-99.8%, and the specificity was 99.9% (855/856), 95% CI: 99.4-99.9%.

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

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.

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

BMJ ◽  
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.

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

Viruses ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 684
Author(s):  
Miroslav Homza ◽  
Hana Zelena ◽  
Jaroslav Janosek ◽  
Hana Tomaskova ◽  
Eduard Jezo ◽  
...  
Keyword(s):  
False Negative ◽  
Antigen Test ◽  
Rt Pcr ◽  
False Negatives ◽  
Predictive Values ◽  
Asymptomatic Patients ◽  
High Prevalence ◽  
Antigen Tests ◽  
Antigen Testing ◽  
Excellent Tool

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.

scholarly journals Use of Immunochromatographic SARS-CoV-2 Antigen Testing in Eight Long-Term Care Facilities for the Elderly

Healthcare ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 868
Author(s):  
Martina Ifko ◽  
Miha Skvarc
Keyword(s):  
Long Term Care ◽  
Health Care Facilities ◽  
Accurate Information ◽  
Clinical Validation ◽  
Antigen Test ◽  
Term Care ◽  
Care Facilities ◽  
Antigen Tests ◽  
Antigen Testing

The clinical validation of the NADAL COVID-19 antigen test (Nal von Minden, Moers, Germany) started in eight Slovenian long-term health care facilities in October 2020. The purpose of clinical validation is to implement the test into the everyday working process in long-term care (LTC) facilities and demonstrate how it can be used to mitigate the spread of the virus in these environments. The facilities compared the results of antigen tests to the results obtained using Cobas 6800 SARS-CoV-2 real-time reverse transcription polymerase chain reaction (RT-PCR) (Roche, USA). Sensitivity (86.96%, 95% CI: 66.41–97.23%) and specificity (88.24%, 95% CI: 80.35–93.77%) of the NADAL COVID-19 antigen test were good. Rapid antigen testing served well for early detection of infection and helped to prevent and control spread of the SARS Cov2 in six out of eight LTCs. Moreover, mini-outbreaks were quickly resolved in all six LTCs. Locally validated immunochromatographic SARS-CoV-2 antigen testing can be used to contain the spread of the virus in LTCs. Antigen tests also deliver accurate information very quickly if used early with a low threshold. The NADAL COVID-19 antigen test proved to be a good screening tool to detect SARS-COV-2 in LTCs.

scholarly journals Performance characteristics of a rapid SARS-CoV-2 antigen detection assay at a public plaza testing site in San Francisco

2021 ◽  
Author(s):  
Genay Pilarowski ◽  
Paul Lebel ◽  
Sara Sunshine ◽  
Jamin Liu ◽  
Emily Crawford ◽  
...  
Keyword(s):  
Viral Load ◽  
San Francisco ◽  
High Viral Load ◽  
Performance Characteristics ◽  
Viral Rna ◽  
Antigen Test ◽  
Rt Pcr ◽  
Detection Assay ◽  
Community Transmission ◽  
Testing Site

Abstract We evaluated the performance of the Abbott BinaxNOW TM Covid-19 rapid antigen test (Binax-CoV2) to detect virus among persons, regardless of symptoms, at a public plaza site of ongoing community transmission. Titration with cultured SARS-CoV-2 yielded a human observable threshold between 1.6x10 4-4.3x10 4 viral RNA copies (cycle threshold (Ct) of 30.3-28.8). Among 878 subjects tested, 3% (26/878) were positive by RT-PCR, of which 15/26 had Ct&lt;30, indicating high viral load. 40% (6/15) of Ct&lt;30 were asymptomatic. Using this Ct&lt;30 threshold for Binax-CoV2 evaluation, the sensitivity of Binax-CoV2 was 93.3% (14/15), 95% CI: 68.1-99.8%, and the specificity was 99.9% (855/856), 95% CI: 99.4-99.9%.

scholarly journals Infection and infectivity: Utility of rapid antigen tests for the diagnosis of COVID-19

2021 ◽  
Vol 34 (Suppl 1) ◽  
pp. 46-48
Author(s):  
Pablo Barreiro ◽  
Jesús San-Román ◽  
María del Mar Carretero ◽  
Francisco Javier Candel ◽  
Keyword(s):  
Viral Load ◽  
Point Of Care ◽  
Viral Transmission ◽  
Lateral Flow ◽  
Pretest Probability ◽  
Antigen Test ◽  
Diagnostic Strategies ◽  
Antigen Tests ◽  
Asymptomatic Individuals

Detection of SARS-CoV-2 proteins is commercially available in the form of lateral-flow rapid antigen test for the point-of-care diagnosis of COVID-19. This platform has been validated for symptomatic and asymptomatic individuals, for diagnosis or screening, and as part of single or sequential diagnostic strategies. Although in general less sensitive than amplification techniques, antigen tests may be particularly valid during the first days of symptoms and to detect individuals with greater viral load, thereby with enhanced chances of viral transmission. The simplicity of antigen tests make them very suitable to discard infection in settings with low pretest probability, and to detect infection in case of higher chances of having COVID-19.

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