Comparison of the Quantitative DiaSorin Liaison Antigen Test to Reverse Transcription-PCR for the Diagnosis of COVID-19 in Symptomatic and Asymptomatic Outpatients

Performance characteristics of INDICAID antigen rapid diagnostic test on SARS-CoV-2 samples during the omicron wave in Cameroon

Background

WHO recommends the use of COVID-19 antigen rapid diagnostic tests (Ag-RDT) with at least 80 % sensitivity and 97 % specificity. In the era of Omicron variants, we sought to ascertain the performance of the INDICAID™ Ag-RDT compared to real-time PCR (RT-PCR) as the gold standard.

Methods

A laboratory-based study was conducted among consenting individuals tested for COVID-19 at the virology laboratory of the Chantal BIYA International Reference Centre, Yaoundé-Cameron. The samples were processed by INDICAID™ Ag-RDT and DaAn Gene real-time PCR according to the manufacturer's instructions, and PCR-results were interpreted as per cycle thresholds (CT). The sensitivity, specificity, positive and negative predictive values (PPV and NVP) of INDICAID™ Ag-RDT were evaluated according to PCR CT-values.

Results

A total of 565 nasopharyngeal swabs were collected from participants (median age [IQR]: 40 [31-75]; M/F sex-ratio was 1.2 and 380 were vaccinated). Following PCR, overall COVID-19 positivity was 5.66 %. For CT < 37, INDICAID™ Ag-RDT sensitivity was 21.9 % (95%CI: [8.3-39.9]), specificity 100 % (95%CI: [99.3-100]); PPV 100 % (95%CI: [59.0-100]), NPV 95.5 % (95%CI: [93.4-97.1]) and kappa = 0.34 (95%CI: [0.19-0.35]). For CT < 25, sensitivity was 100 % (95%CI: [47.8-100.0]), specificity 99.6 % (95%CI: [98.7-99.9]); PPV 94.4 % (95%CI: [51.7-100]), NPV 100 % (95%CI: [99.3-100]) and kappa = 0.83 (95%CI: [0.6-1.0]). COVID-19 sequences generated were all Omicron BA.1 subvariants.

Conclusion

For patients infected with high viral loads (CT < 25), INDICAID™ Ag-RDT has high intrinsic (sensitivity and specificity) and extrinsic (predictive values) performances for COVID-19 diagnosis. Due to its simplicity and short turnaround time, INDICAID™ Ag-RDT is, therefore a reliable tool to prevent the spread of COVID-19 at community level in the current era of Omicron subvariants.

Clinical accuracy of instrument-based SARS-CoV-2 antigen diagnostic tests: a systematic review and meta-analysis

BACKGROUND

During the COVID-19 pandemic, antigen diagnostic tests were frequently used for screening, triage, and diagnosis. Novel instrument-based antigen tests (iAg tests) hold the promise of outperforming their instrument-free, visually-read counterparts. Here, we provide a systematic review and meta-analysis of the SARS-CoV-2 iAg tests' clinical accuracy.

METHODS

We systematically searched MEDLINE (via PubMed), Web of Science, medRxiv, and bioRxiv for articles published before November 7th, 2022, evaluating the accuracy of iAg tests for SARS-CoV-2 detection. We performed a random effects meta-analysis to estimate sensitivity and specificity and used the QUADAS-2 tool to assess study quality and risk of bias. Sub-group analysis was conducted based on Ct value range, IFU-conformity, age, symptom presence and duration, and the variant of concern.

RESULTS

We screened the titles and abstracts of 20,431 articles and included 114 publications that fulfilled the inclusion criteria. Additionally, we incorporated three articles sourced from the FIND website, totaling 117 studies encompassing 95,181 individuals, which evaluated the clinical accuracy of 24 commercial COVID-19 iAg tests. The studies varied in risk of bias but showed high applicability. Of 24 iAg tests from 99 studies assessed in the meta-analysis, the pooled sensitivity and specificity compared to molecular testing of a paired NP swab sample were 76.7% (95% CI 73.5 to 79.7) and 98.4% (95% CI 98.0 to 98.7), respectively. Higher sensitivity was noted in individuals with high viral load (99.6% [95% CI 96.8 to 100] at Ct-level ≤ 20) and within the first week of symptom onset (84.6% [95% CI 78.2 to 89.3]), but did not differ between tests conducted as per manufacturer's instructions and those conducted differently, or between point-of-care and lab-based testing.

CONCLUSION

Overall, iAg tests have a high pooled specificity but a moderate pooled sensitivity, according to our analysis. The pooled sensitivity increases with lower Ct-values (a proxy for viral load), or within the first week of symptom onset, enabling reliable identification of most COVID-19 cases and highlighting the importance of context in test selection. The study underscores the need for careful evaluation considering performance variations and operational features of iAg tests.

Automated antigen assays display a high heterogeneity for the detection of SARS-CoV-2 variants of concern, including several Omicron sublineages

Diagnostic tests for direct pathogen detection have been instrumental to contain the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) pandemic. Automated, quantitative, laboratory-based nucleocapsid antigen (Ag) tests for SARS-CoV-2 have been launched alongside nucleic acid-based test systems and point-of-care (POC) lateral-flow Ag tests. Here, we evaluated four commercial Ag tests on automated platforms for the detection of different sublineages of the SARS-CoV-2 Omicron variant of concern (VoC) (B.1.1.529) in comparison with "non-Omicron" VoCs. A total of 203 Omicron PCR-positive respiratory swabs (53 BA.1, 48 BA.2, 23 BQ.1, 39 XBB.1.5 and 40 other subvariants) from the period February to March 2022 and from March 2023 were examined. In addition, tissue culture-expanded clinical isolates of Delta (B.1.617.2), Omicron-BA.1, -BF.7, -BN.1 and -BQ.1 were studied. These results were compared to previously reported data from 107 clinical "non-Omicron" samples from the end of the second pandemic wave (February to March 2021) as well as cell culture-derived samples of wildtype (wt) EU-1 (B.1.177), Alpha VoC (B.1.1.7) and Beta VoC (B.1.351)). All four commercial Ag tests were able to detect at least 90.9% of Omicron-containing samples with high viral loads (Ct < 25). The rates of true-positive test results for BA.1/BA.2-positive samples with intermediate viral loads (Ct 25-30) ranged between 6.7% and 100.0%, while they dropped to 0 to 15.4% for samples with low Ct values (> 30). This heterogeneity was reflected also by the tests' 50%-limit of detection (LoD50) values ranging from 44,444 to 1,866,900 Geq/ml. Respiratory samples containing Omicron-BQ.1/XBB.1.5 or other Omicron subvariants that emerged in 2023 were detected with enormous heterogeneity (0 to 100%) for the intermediate and low viral load ranges with LoD50 values between 23,019 and 1,152,048 Geq/ml. In contrast, detection of "non-Omicron" samples was more sensitive, scoring positive in 35 to 100% for the intermediate and 1.3 to 32.9% of cases for the low viral loads, respectively, corresponding to LoD50 values ranging from 6181 to 749,792 Geq/ml. All four assays detected cell culture-expanded VoCs Alpha, Beta, Delta and Omicron subvariants carrying up to six amino acid mutations in the nucleocapsid protein with sensitivities comparable to the non-VoC EU-1. Overall, automated quantitative SARS-CoV-2 Ag assays are not more sensitive than standard rapid antigen tests used in POC settings and show a high heterogeneity in performance for VoC recognition. The best of these automated Ag tests may have the potential to complement nucleic acid-based assays for SARS-CoV-2 diagnostics in settings not primarily focused on the protection of vulnerable groups. In light of the constant emergence of new Omicron subvariants and recombinants, most recently the XBB lineage, these tests' performance must be regularly re-evaluated, especially when new VoCs carry mutations in the nucleocapsid protein or immunological and clinical parameters change.

The evaluation results of proposed antigen rapid diagnostic tests for COVID-19: some possible factors might influence

PURPOSE

In addition to existing gold standard qRT-PCR methods, there is a need to develop reliable rapid tests for infection control with early notification of COVID-19 cases to enable effective outbreak management. We evaluated the validity of the three Ag-RDT kits proposed by some companies in different countries by using qRT-PCR and analyzed its results.

METHODS

Each of the three Ag-RDT kits (namely A, B, and C) was tested with 90 samples, consisting of samples with Ct ≤ 25, samples with Ct > 25, and negative SARS-CoV-2 PCR samples.

RESULTS

This study showed that for samples with Ct > 25, all the three kits could not detect SARS-CoV-2 Ag (0% sensitivity) but showed 100% specificity. Meanwhile, for samples with Ct ≤ 25, kit C was the best (76.7% sensitivity and 100% specificity). The PPV of the three kits was 100%, but their NPV ranged 63-84.8%. Kit C showed the best accuracy (89.9%). Some factors might influence the results of evaluation, such as variation of virus proteins and transportation-storage of the kits.

CONCLUSION

The overall specificity of the three kits for all samples was high; however, all of them have not met the minimum performance requirements of ≥ 80% sensitivity for samples with Ct ≤ 25. The validation test is much necessary to be carried out by the authority in national health care to ensure the feasibility of the kit for point-of-care testing (POCT) of COVID-19. Some factors that might influence should be anticipated to increase their sensitivities and specificities.

Association Between Rapid Antigen Detection Tests and Real-Time Reverse Transcription-Polymerase Chain Reaction Assay for SARS-CoV-2: A Systematic Review and Meta-Analyses

Objectives: We aimed to assess the association between rapid antigen detection tests and real-time reverse transcription-polymerase chain reaction assay for severe acute respiratory syndrome coronavirus 2. Methods: We searched PubMed, Cochrane Library, EMBASE, and the Web of Science from their inception to 31 May 2023. A random-effects meta-analysis was used to estimate false positives in the RADTs group, relative to those in the RT-PCR group, and subgroup analyses were conducted based on the different Ct value cut-offs (<40 or ≥40). We performed this study in accordance with the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Results: Fifty-one studies were included and considered to be of moderate quality. We found a satisfactory overall false positive rate (0.01, 95% CI: 0.00-0.01) for the RADTs compared to RT-PCR. In the stratified analysis, we also found that the false positive rates of the RADTs did not increase when Ct values of RT-PCR (Ct < 40, 0.01, 95% CI: 0.00-0.01; Ct ≥ 40, 0.01, 95% CI: 0.00-0.01). Conclusion: In conclusion, the best available evidence supports an association between RADTs and RT-PCR. When Ct-values were analyzed using cut-off <40 or ≥40, this resulted in an estimated false positive rate of only 1%.

Comparison of performance of LIAISON SARS-CoV-2 antigen assay with RT-PCR during the Omicron wave

Due to the newly emerging Omicron variant, there is a need to re-evaluate the performance of automated antigen tests. Our study aim was to evaluate the performance of the automated Liaison SARS-CoV-2 antigen assay against reverse transcriptase polymerase chain reaction (RT-PCR) in samples with Omicron variant.A prospective study was performed on 373 combined oro-nasopharyngeal samples (NPS) randomly collected from symptomatic patients. NPS were tested with Liaison SARS-CoV-2 Ag test (DiaSorin, Italy) and DS Coronex COVID-19 Multiplex RT-PCR Diagnosis Kit (DS BioTechnology, Ankara, Turkey).Of 373 samples, 124 (33.2%) were found to be RT-PCR positive and 249 (66.8%) RT-PCR negative. Taking RT-PCR as a reference, the sensitivity and specificity of the Liaison SARS-CoV-2 Ag assay were found as 84.6% (95%CI 77.3%-90%) and 100% (95%CI 98.5%-100%), respectively. For samples with a cycle threshold (Ct) value <25 (high viral load), the sensitivity increased to 100%. When antigen concentration and Ct values were compared, a strong negative correlation between antigen and Ct values was determined (P < 0.001).The Liaison antigen test met the performance criteria recommended by the WHO for samples with the Omicron variant. In addition, it showed excellent sensitivity and specificity in patients with high viral load. Therefore, Liaison antigen test can be a reliable and useful alternative in the diagnosis of SARS-CoV-2 infection, particularly in resource-constrained laboratories.

The Use of Biological Sensors and Instrumental Analysis to Discriminate COVID-19 Odor Signatures

The spread of SARS-CoV-2, which causes the disease COVID-19, is difficult to control as some positive individuals, capable of transmitting the disease, can be asymptomatic. Thus, it remains critical to generate noninvasive, inexpensive COVID-19 screening systems. Two such methods include detection canines and analytical instrumentation, both of which detect volatile organic compounds associated with SARS-CoV-2. In this study, the performance of trained detection dogs is compared to a noninvasive headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) approach to identifying COVID-19 positive individuals. Five dogs were trained to detect the odor signature associated with COVID-19. They varied in performance, with the two highest-performing dogs averaging 88% sensitivity and 95% specificity over five double-blind tests. The three lowest-performing dogs averaged 46% sensitivity and 87% specificity. The optimized linear discriminant analysis (LDA) model, developed using HS-SPME-GC-MS, displayed a 100% true positive rate and a 100% true negative rate using leave-one-out cross-validation. However, the non-optimized LDA model displayed difficulty in categorizing animal hair-contaminated samples, while animal hair did not impact the dogs' performance. In conclusion, the HS-SPME-GC-MS approach for noninvasive COVID-19 detection more accurately discriminated between COVID-19 positive and COVID-19 negative samples; however, dogs performed better than the computational model when non-ideal samples were presented.

Clinical evaluation of an automated, rapid mariPOC antigen test in screening of symptomatics and asymptomatics for SARS-CoV-2 infection

A novel automated mariPOC SARS-CoV-2 antigen test was evaluated in a Health Care Center Laboratory among symptomatic and asymptomatic individuals seeking SARS-CoV-2 testing. According to the national testing strategy, reverse transcription polymerase chain reaction (RT-PCR) was used as a reference method. A total of 962 subjects were included in this study, 4.8% (46/962) of their samples were SARS-CoV-2 RT-PCR-positive, and 87% (40/46) of these were from symptomatics. Among the symptomatics, the overall sensitivity of the mariPOC SARS-CoV-2 test was 82.5% (33/40), though the sensitivity increased to 97.1% (33/34) in samples with a C_t  < 30. The mariPOC SARS-CoV-2 test detected two of six PCR-positive samples among the asymptomatics, four cases that remained antigen test negative had C_t values between 28 and 36. The specificity of the mariPOC SARS-CoV-2 test was 100% (916/916). The evaluation showed that the mariPOC SARS-CoV-2 rapid antigen test is very sensitive and specific for the detection of individuals who most probably are contagious.

Systematic Review of Diagnostic Accuracy of DiaSorin Liaison SARS-CoV-2 Antigen Immunoassay

Background

Quantification of SARS-CoV-2 antigens by means of rapid, high-throughput and fully-automated techniques has been proposed as a feasible alternative to overcome the current shortage of resources for routine molecular diagnostics. To this end, we provide here a systematic review of diagnostic accuracy of DiaSorin Liaison SARS-CoV-2 antigen immunoassay.

Methods

An electronic search was conduced in Medline and Scopus, with no language or date restrictions (up to January 20, 2022), for identifying all published studies articles in which the diagnostic performance of the DiaSorin Liaison SARS-CoV-2 antigen immunoassay was compared with molecular diagnostic techniques.

Results

The electronic search identified a final number of 11 studies, totalling 4449 oro- and naso-pharyngeal specimens. The pooled diagnostic sensitivity, specificity and area under the curve (AUC) of the Liaison SARS-CoV-2 antigen immunoassay in all samples were 0.51 (95%CI, 0.49-0.54), 1.00 (95%CI, 1.00-1.00) and 0.994 (95%CI, 0.990-0.998), respectively, whilst the overall concordance with molecular diagnostics was 82.1%. The pooled diagnostic sensitivity, specificity and AUC of the Liaison SARS-CoV-2 antigen immunoassay in specimens with high viral load (i.e., cycle threshold values <25-30) were 0.79 (95%CI, 0.75-0.82), 1.00 (95%CI, 0.99-1.00) and 0.911 (95%CI, 0.879-0.943), respectively, whilst the overall concordance with molecular diagnostics in such samples increased to 94.2%.

Conclusion

The results of this systematic literature review suggest that there is sufficient accuracy of the DiaSorin Liaison SARS-CoV-2 antigen immunoassay in samples with high viral loads that would enable its reliable usage for identifying superspreaders, who are responsible for the vast majority of transmission events.

Rapid, point-of-care antigen tests for diagnosis of SARS-CoV-2 infection

BACKGROUND

Accurate rapid diagnostic tests for SARS-CoV-2 infection would be a useful tool to help manage the COVID-19 pandemic. Testing strategies that use rapid antigen tests to detect current infection have the potential to increase access to testing, speed detection of infection, and inform clinical and public health management decisions to reduce transmission. This is the second update of this review, which was first published in 2020.

OBJECTIVES

To assess the diagnostic accuracy of rapid, point-of-care antigen tests for diagnosis of SARS-CoV-2 infection. We consider accuracy separately in symptomatic and asymptomatic population groups. Sources of heterogeneity investigated included setting and indication for testing, assay format, sample site, viral load, age, timing of test, and study design.

SEARCH METHODS

We searched the COVID-19 Open Access Project living evidence database from the University of Bern (which includes daily updates from PubMed and Embase and preprints from medRxiv and bioRxiv) on 08 March 2021. We included independent evaluations from national reference laboratories, FIND and the Diagnostics Global Health website. We did not apply language restrictions.

SELECTION CRITERIA

We included studies of people with either suspected SARS-CoV-2 infection, known SARS-CoV-2 infection or known absence of infection, or those who were being screened for infection. We included test accuracy studies of any design that evaluated commercially produced, rapid antigen tests. We included evaluations of single applications of a test (one test result reported per person) and evaluations of serial testing (repeated antigen testing over time). Reference standards for presence or absence of infection were any laboratory-based molecular test (primarily reverse transcription polymerase chain reaction (RT-PCR)) or pre-pandemic respiratory sample.

DATA COLLECTION AND ANALYSIS

We used standard screening procedures with three people. Two people independently carried out quality assessment (using the QUADAS-2 tool) and extracted study results. Other study characteristics were extracted by one review author and checked by a second. We present sensitivity and specificity with 95% confidence intervals (CIs) for each test, and pooled data using the bivariate model. We investigated heterogeneity by including indicator variables in the random-effects logistic regression models. We tabulated results by test manufacturer and compliance with manufacturer instructions for use and according to symptom status.

MAIN RESULTS

We included 155 study cohorts (described in 166 study reports, with 24 as preprints). The main results relate to 152 evaluations of single test applications including 100,462 unique samples (16,822 with confirmed SARS-CoV-2). Studies were mainly conducted in Europe (101/152, 66%), and evaluated 49 different commercial antigen assays. Only 23 studies compared two or more brands of test. Risk of bias was high because of participant selection (40, 26%); interpretation of the index test (6, 4%); weaknesses in the reference standard for absence of infection (119, 78%); and participant flow and timing 41 (27%). Characteristics of participants (45, 30%) and index test delivery (47, 31%) differed from the way in which and in whom the test was intended to be used. Nearly all studies (91%) used a single RT-PCR result to define presence or absence of infection. The 152 studies of single test applications reported 228 evaluations of antigen tests. Estimates of sensitivity varied considerably between studies, with consistently high specificities. Average sensitivity was higher in symptomatic (73.0%, 95% CI 69.3% to 76.4%; 109 evaluations; 50,574 samples, 11,662 cases) compared to asymptomatic participants (54.7%, 95% CI 47.7% to 61.6%; 50 evaluations; 40,956 samples, 2641 cases). Average sensitivity was higher in the first week after symptom onset (80.9%, 95% CI 76.9% to 84.4%; 30 evaluations, 2408 cases) than in the second week of symptoms (53.8%, 95% CI 48.0% to 59.6%; 40 evaluations, 1119 cases). For those who were asymptomatic at the time of testing, sensitivity was higher when an epidemiological exposure to SARS-CoV-2 was suspected (64.3%, 95% CI 54.6% to 73.0%; 16 evaluations; 7677 samples, 703 cases) compared to where COVID-19 testing was reported to be widely available to anyone on presentation for testing (49.6%, 95% CI 42.1% to 57.1%; 26 evaluations; 31,904 samples, 1758 cases). Average specificity was similarly high for symptomatic (99.1%) or asymptomatic (99.7%) participants. We observed a steady decline in summary sensitivities as measures of sample viral load decreased. Sensitivity varied between brands. When tests were used according to manufacturer instructions, average sensitivities by brand ranged from 34.3% to 91.3% in symptomatic participants (20 assays with eligible data) and from 28.6% to 77.8% for asymptomatic participants (12 assays). For symptomatic participants, summary sensitivities for seven assays were 80% or more (meeting acceptable criteria set by the World Health Organization (WHO)). The WHO acceptable performance criterion of 97% specificity was met by 17 of 20 assays when tests were used according to manufacturer instructions, 12 of which demonstrated specificities above 99%. For asymptomatic participants the sensitivities of only two assays approached but did not meet WHO acceptable performance standards in one study each; specificities for asymptomatic participants were in a similar range to those observed for symptomatic people. At 5% prevalence using summary data in symptomatic people during the first week after symptom onset, the positive predictive value (PPV) of 89% means that 1 in 10 positive results will be a false positive, and around 1 in 5 cases will be missed. At 0.5% prevalence using summary data for asymptomatic people, where testing was widely available and where epidemiological exposure to COVID-19 was suspected, resulting PPVs would be 38% to 52%, meaning that between 2 in 5 and 1 in 2 positive results will be false positives, and between 1 in 2 and 1 in 3 cases will be missed.

AUTHORS' CONCLUSIONS

Antigen tests vary in sensitivity. In people with signs and symptoms of COVID-19, sensitivities are highest in the first week of illness when viral loads are higher. Assays that meet appropriate performance standards, such as those set by WHO, could replace laboratory-based RT-PCR when immediate decisions about patient care must be made, or where RT-PCR cannot be delivered in a timely manner. However, they are more suitable for use as triage to RT-PCR testing. The variable sensitivity of antigen tests means that people who test negative may still be infected. Many commercially available rapid antigen tests have not been evaluated in independent validation studies. Evidence for testing in asymptomatic cohorts has increased, however sensitivity is lower and there is a paucity of evidence for testing in different settings. Questions remain about the use of antigen test-based repeat testing strategies. Further research is needed to evaluate the effectiveness of screening programmes at reducing transmission of infection, whether mass screening or targeted approaches including schools, healthcare setting and traveller screening.

Diagnostic utility and performance of rapid antigen test in SARS CoV- 2 in symptomatic and asymptomatic patients during the second pandemic wave in Kashmir, North India

Purpose

Real time reverse transcriptase PCR (rRT PCR) although gold standard test for the diagnosis of SARS CoV-2, carries disadvantages of a sophisticated set up, long time to results and centralized services. The rapid antigen tests (RAT) can be used as a primary screening tool with the advantages of rapid turnaround time and ease of use. The study was conducted to determine the performance of rapid antigen test (standard Q COVID 19 Ag) in comparison to rRT PCR in symptomatic patients and asymptomatic contacts and asymptomatic patients with no apparent contact history.

Methods

Nasopharyngeal swabs taken in duplicate from 1034 patients were collected over a 5 months period. These included 248 (23.98%) symptomatic, 386 (37.34%) asymptomatic contacts and 400 (38.68%) asymptomatic subjects who were routinely screened in pre-operative period, as a prerequisite for travel, or pregnant females. Both rRT PCR and RAT were performed as per manufacturers’ instructions. Performance of test in different subgroups of patients was evaluated. Performance of RAT test on basis of duration of illness and Ct values was also analyzed.

Results

In this study, 445 (43.04%) were rRT PCR positive, out of which 374 samples were RAT positive as well. 31 samples were RAT positive but PCR negative. The sensitivity, specificity, PPV and NPV of the rapid antigen test was 84.04%, 94.74%, 92.35% and 88.71% respectively. The negative predictive value of the test in asymptomatic patients without any significant contact history was 97.07%.

Conclusions

This study recommends the use of the antigen test as a method of diagnosis for SARS CoV-2. However a negative result with RAT in suspected patients and their contacts should be viewed with caution. This study also finds the utility of using RAT test in the community settings as a screening test in schools, colleges and mass gatherings.

Evaluation of a laboratory-based high-throughput SARS-CoV-2 antigen assay

OBJECTIVES

Antigen tests are an essential part of SARS-CoV-2 testing strategies. Rapid antigen tests are easy to use but less sensitive compared to nucleic acid amplification tests (NAT) and less suitable for large-scale testing. In contrast, laboratory-based antigen tests are suitable for high-throughput immunoanalyzers. Here we evaluated the diagnostic performance of the laboratory-based Siemens Healthineers SARS-CoV-2 Antigen (CoV2Ag) assay.

METHODS

In a public test center, from 447 individuals anterior nasal swab specimens as well as nasopharyngeal swab specimens were collected. The nasal swab specimens were collected in sample inactivation medium and measured using the CoV2Ag assay. The nasopharyngeal swab specimens were measured by RT-PCR. Additionally, 9,046 swab specimens obtained for screening purposes in a tertiary care hospital were analyzed and positive CoV2Ag results confirmed by NAT.

RESULTS

In total, 234/447 (52.3%) participants of the public test center were positive for SARS-CoV-2-RNA. Viral lineage B1.1.529 was dominant during the study. Sensitivity and specificity of the CoV2Ag assay were 88.5% (95%CI: 83.7-91.9%) and 99.5% (97.4-99.9%), respectively. Sensitivity increased to 93.7% (97.4-99.9%) and 98.7% (97.4-99.9%) for swab specimens with cycle threshold values <30 and <25, respectively. Out of 9,046 CoV2Ag screening tests from hospitalized patients, 21 (0.2%) swab specimens were determined as false-positive by confirmatory NAT.

CONCLUSIONS

Using sample tubes containing inactivation medium the laboratory-based high-throughput CoV2Ag assay is a very specific and highly sensitive assay for detection of SARS-CoV-2 antigen in nasal swab specimens including the B1.1.529 variant. In low prevalence settings confirmation of positive CoV2Ag results by SARS-CoV-2-RNA testing is recommended.

Performance of Antigen Detection Tests for SARS-CoV-2: A Systematic Review and Meta-Analysis

Coronavirus disease 2019 (COVID-19) initiated global health care challenges such as the necessity for new diagnostic tests. Diagnosis by real-time PCR remains the gold-standard method, yet economical and technical issues prohibit its use in points of care (POC) or for repetitive tests in populations. A lot of effort has been exerted in developing, using, and validating antigen-based tests (ATs). Since individual studies focus on few methodological aspects of ATs, a comparison of different tests is needed. Herein, we perform a systematic review and meta-analysis of data from articles in PubMed, medRxiv and bioRxiv. The bivariate method for meta-analysis of diagnostic tests pooling sensitivities and specificities was used. Most of the AT types for SARS-CoV-2 were lateral flow immunoassays (LFIA), fluorescence immunoassays (FIA), and chemiluminescence enzyme immunoassays (CLEIA). We identified 235 articles containing data from 220,049 individuals. All ATs using nasopharyngeal samples show better performance than those with throat saliva (72% compared to 40%). Moreover, the rapid methods LFIA and FIA show about 10% lower sensitivity compared to the laboratory-based CLEIA method (72% compared to 82%). In addition, rapid ATs show higher sensitivity in symptomatic patients compared to asymptomatic patients, suggesting that viral load is a crucial parameter for ATs performed in POCs. Finally, all methods perform with very high specificity, reaching around 99%. LFIA tests, though with moderate sensitivity, appear as the most attractive method for use in POCs and for performing seroprevalence studies.

Diagnostic Performance of Antigen Rapid Diagnostic Tests, Chest Computed Tomography, and Lung Point-of-Care-Ultrasonography for SARS-CoV-2 Compared with RT-PCR Testing: A Systematic Review and Network Meta-Analysis

(1) Background: The comparative performance of various diagnostic methods for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection remains unclear. This study aimed to investigate the comparison of the 3 index test performances of rapid antigen diagnostic tests (RDTs), chest computed tomography (CT), and lung point-of-care-ultrasonography (US) with reverse transcription-polymerase chain reaction (RT-PCR), the reference standard, to provide more evidence-based data on the appropriate use of these index tests. (2) Methods: We retrieved data from electronic literature searches of PubMed, Cochrane Library, and EMBASE from 1 January 2020, to 1 April 2021. Diagnostic performance was examined using bivariate random-effects diagnostic test accuracy (DTA) and Bayesian network meta-analysis (NMA) models. (3) Results: Of the 3992 studies identified in our search, 118 including 69,445 participants met our selection criteria. Among these, 69 RDT, 38 CT, and 15 US studies in the pairwise meta-analysis were included for DTA with NMA. CT and US had high sensitivity of 0.852 (95% credible interval (CrI), 0.791–0.914) and 0.879 (95% CrI, 0.784–0.973), respectively. RDT had high specificity, 0.978 (95% CrI, 0.960–0.996). In accuracy assessment, RDT and CT had a relatively higher than US. However, there was no significant difference in accuracy between the 3 index tests. (4) Conclusions: This meta-analysis suggests that, compared with the reference standard RT-PCR, the 3 index tests (RDTs, chest CT, and lung US) had similar and complementary performances for diagnosis of SARS-CoV-2 infection. To manage and control COVID-19 effectively, future large-scale prospective studies could be used to obtain an optimal timely diagnostic process that identifies the condition of the patient accurately.

COVID-19 Infections in Cancer Patients Were Frequently Asymptomatic: Description From a French Prospective Multicenter Cohort (PAPESCO-19)

Background

Cancer patients (CPs) are considered more vulnerable and as a high mortality group regarding COVID-19. In this analysis, we aimed to describe asymptomatic COVID (+) CPs and associated factors.

Methods

We conducted a prospective study in CPs and health care workers (HCWs) in 4 French cancer centers (PAPESCO [PAtients et PErsonnels de Santé des Centres de Lutte Contre le Cancer pendant l'épidémie de COvid-19] study). This analysis used data recorded between June 17, 2020 and November 30, 2020 in CPs (first 2 waves, no variants). At inclusion and quarterly, CPs reported the presence of predefined COVID-19 symptoms and had a blood rapid diagnostic test; a reverse transcription polymerase chain reaction (RT-PCR) was done in case of suspected infection.

Results

A total 878 CPs were included; COVID-19 prevalence was similar in both CPs (8%) and HCWs (9.5%); of the 70 CPs (8%) who were COVID (+), 29 (41.4%) were and remained asymptomatic; 241/808 of the COVID (-) (29.8%) were symptomatic. 18 COVID (+) were hospitalized (2% of CPs), 1 in intensive care unit (ICU) and 1 died (0.1% of CPs and 2.4% of symptomatic COVID [+] CPs). Only the inclusion center was associated with clinical presentation (in Nancy, Angers, Nantes, and Clermont-Ferrand: 65.4%, 35%, 28.6%, and 10% CPs were asymptomatic, respectively).

Conclusions

Seroprevalence of COVID-19 in CPs was similar to that observed in HCWs; mortality related to COVID-19 among CPs was 0.1%. More than 40% of COVID (+) CPs were asymptomatic and one third of COVID (-) CPs had symptoms. Only geographic origin was associated with the presence or absence of symptoms. Social distancing and protective measures must be applied in CPs at home and when hospitalized.

Saliva-based COVID-19 detection: A rapid antigen test of SARS-CoV-2 nucleocapsid protein using an electrical-double-layer gated field-effect transistor-based biosensing system

Facing the unstopped surges of COVID-19, an insufficient capacity of diagnostic testing jeopardizes the control of disease spread. Due to a centralized setting and a long turnaround, real-time reverse transcription polymerase chain reaction (real-time RT-PCR), the gold standard of viral detection, has fallen short in timely reflecting the epidemic status quo during an urgent outbreak. As such, a rapid screening tool is necessitated to help contain the spread of COVID-19 amid the countries where the vaccine implementations have not been widely deployed. In this work, we propose a saliva-based COVID-19 antigen test using the electrical double layer (EDL)-gated field-effect transistor-based biosensor (BioFET). The detection of SARS-CoV-2 nucleocapsid (N) protein is validated with limits of detection (LoDs) of 0.34 ng/mL (7.44 pM) and 0.14 ng/mL (2.96 pM) in 1× PBS and artificial saliva, respectively. The specificity is inspected with types of antigens, exhibiting low cross-reactivity among MERS-CoV, Influenza A virus, and Influenza B virus. This portable system is embedded with Bluetooth communication and user-friendly interfaces that are fully compatible with digital health, feasibly leading to an on-site turnaround, an effective management, and a proactive response taken by medical providers and frontline health workers.

Saliva-based COVID-19 detection: A rapid antigen test of SARS-CoV-2 nucleocapsid protein using an electrical-double-layer gated field-effect transistor-based biosensing system

Facing the unstopped surges of COVID-19, an insufficient capacity of diagnostic testing jeopardizes the control of disease spread. Due to a centralized setting and a long turnaround, real-time reverse transcription polymerase chain reaction (real-time RT-PCR), the gold standard of viral detection, has fallen short in timely reflecting the epidemic status quo during an urgent outbreak. As such, a rapid screening tool is necessitated to help contain the spread of COVID-19 amid the countries where the vaccine implementations have not been widely deployed. In this work, we propose a saliva-based COVID-19 antigen test using the electrical double layer (EDL)-gated field-effect transistor-based biosensor (BioFET). The detection of SARS-CoV-2 nucleocapsid (N) protein is validated with limits of detection (LoDs) of 0.34 ng/mL (7.44 pM) and 0.14 ng/mL (2.96 pM) in 1× PBS and artificial saliva, respectively. The specificity is inspected with types of antigens, exhibiting low cross-reactivity among MERS-CoV, Influenza A virus, and Influenza B virus. This portable system is embedded with Bluetooth communication and user-friendly interfaces that are fully compatible with digital health, feasibly leading to an on-site turnaround, an effective management, and a proactive response taken by medical providers and frontline health workers.

Evaluation and Modelling of the Performance of an Automated SARS-CoV-2 Antigen Assay According to Sample Type, Target Population and Epidemic Trends

The Lumipulse^® G SARS-CoV-2 Ag assay performance was evaluated on prospectively collected saliva and nasopharyngeal swabs (NPS) of recently ill in- and outpatients and according to the estimated viral load. Performances were calculated using RT-PCR positive NPS from patients with symptoms ≤ 7 days and RT-PCR negative NPS as gold standard. In addition, non-selected positive NPS were analyzed to assess the performances on various viral loads. This assay yielded a sensitivity of 93.1% on NPS and 71.4% on saliva for recently ill patients. For NPS with a viral load > 10³ RNA copies/mL, sensitivity was 96.4%. A model established on our daily routine showed fluctuations of the performances depending on the epidemic trends but an overall good negative predictive value. Lumipulse^® G SARS-CoV-2 assay yielded good performance for an automated antigen detection assay on NPS. Using it for the detection of recently ill patients or to screen high-risk patients could be an interesting alternative to the more expensive RT-PCR.

Analytical Performance of Quantitative DiaSorin Liaison SARS-COV-2 Antigen Test for the Asymptomatic Population

Background: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) antigen (Ag) tests have been widely employed to identify patients for a rapid diagnosis and pandemic control. Rapid lateral-flow techniques are currently the most used, but automated technologies have emerged as another viable alternative to molecular methods. We aimed to evaluate the analytical performance of the DiaSorin Liaison SARS-CoV-2 Ag test in asymptomatic population and close contacts, for its use as a tool in pandemic control efforts.

Material and Methods: A retrospective study was conducted. A total of 861 samples were included, 291 (34%) were positive for SARS-CoV-2 with cycle threshold (Ct) <40, and 570 (66%) were negative.

Results: A strong correlation was observed between reverse transcriptase-PCR (RT-PCR) Ct and Ag 50% Tissue Culture Infectious Dose per milliliter (TCID₅₀/ml; r = 0.6486; p < 0.0001) and all RT-PCR negative samples tested negative for the 200 TCID₅₀/ml SARS-Cov-2 Ag cutoff, i.e., a specificity of 100% was reached (95% CI: 99.4–100.0%). Samples with <25 Ct and/or >10⁶ extrapolated copies/ml were reached a sensitivity of 100% (95% IC 97.0–100.0%). For intermediate viral loads (>10⁵ extrapolated copies/ml or <30 Ct), the sensitivity value still exceeded 80%. As with other Ag methods, samples between 30 and 40 Ct could not be detected with a reliable sensitivity.

Conclusions: The LIAISON® SARS-CoV-2 Ag assay displays an acceptable sensitivity and a very high specificity that is useful for detecting the presence of SARS-CoV-2 in nasal swabs (NPS) of asymptomatic population or to regular monitoring of risk groups in controlled settings. Additionally, the flexibility in processing different samples and in the sampling preparation process makes this test an option for its use in high throughput laboratories. Automated tests may facilitate result reporting and yield consistent data, while avoiding some of the pitfalls of rapid lateral-flow techniques, such as observer variability.

Performance of Rapid Antigen Tests for COVID-19 Diagnosis: A Systematic Review and Meta-Analysis

The identification of viral RNA using reverse transcription quantitative polymerase chain reaction (RT-qPCR) is the gold standard for identifying an infection caused by SARS-CoV-2. The limitations of RT-qPCR such as requirement of expensive instruments, trained staff and laboratory facilities led to development of rapid antigen tests (RATs). The performance of RATs has been widely evaluated and found to be varied in different settings. The present systematic review aims to evaluate the pooled sensitivity and specificity of the commercially available RATs. This review was registered on PROSPERO (registration number: CRD42021278105). Literature search was performed through PubMed, Embase and Cochrane COVID-19 Study Register to search studies published up to 26 August 2021. The overall pooled sensitivity and specificity of RATs and subgroup analyses were calculated. Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) was used to assess the risk of bias in each study. The overall pooled sensitivity and specificity of RATs were 70% (95% CI: 69–71) and 98% (95% CI: 98–98), respectively. In subgroup analyses, nasal swabs showed the highest sensitivity of 83% (95% CI: 80–86) followed by nasopharyngeal swabs 71% (95% CI: 70–72), throat swabs 69% (95% CI: 63–75) and saliva 68% (95% CI: 59–77). Samples from symptomatic patients showed a higher sensitivity of 82% (95% CI: 82–82) as compared to asymptomatic patients at 68% (95% CI: 65–71), while a cycle threshold (Ct) value ≤25 showed a higher sensitivity of 96% (95% CI: 95–97) as compared to higher Ct value. Although the sensitivity of RATs needs to be enhanced, it may still be a viable option in places where laboratory facilities are lacking for diagnostic purposes in the early phase of disease.

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

SARS-CoV-2 viral antigen detection may be an interesting alternative to RT-PCR for the diagnosis of SARS-CoV-2 infection as a less laborious or expensive method but requires validation. This study aimed to compare the performance of the DiaSorin™ LiaisonXL automated quantitative antigen test (QAT) and the AAZ™ rapid antigen test (RAT) to the DiaSorin™ MDX RT-PCR assay. A total of 242 nasopharyngeal samples were tested at La Pitié-Salpêtrière University Hospital (Paris, France). Performances for the detection of variants of SARS-CoV-2 were further investigated. RATs were visually read for qualitative results and band intensity was determined. Overall sensitivity was 63.2% for QAT and 58.6% for RAT. For RT-PCR Ct value 25, sensitivity was 89.8% for both tests. Both tests showed comparable sensitivity for detection of variants. There was a strong relationship between antigen concentration and band positivity. On the same set of samples these tests share similar performances.

Diagnostic Performance of Automated SARS-CoV-2 Antigen Assay in Nasal Swab during COVID-19 Vaccination Campaign

BACKGROUND

To control the spread of the pandemic brought about by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, it is necessary to have an automated reliable diagnostic assay. To date, the RT-PCR (RT-qPCR) has been the recommended laboratory method to diagnose SARS-CoV-2 infection, but there is a need for more automated and reliable tests. The aim of this real-life study was to assess the diagnostic performance of DiaSorin's LIAISON SARS-CoV-2 antigen (Ag) chemiluminescence immunoassay in detecting SARS-CoV-2 in vaccinated and unvaccinated individuals.

METHODS

A prospective study was performed on 300 nasopharyngeal swabs randomly collected from 31 May to 6 July 2021. Nasopharyngeal samples were assayed with DiaSorin's LIAISON SARS-CoV-2 Ag and TaqPath™ COVID-19 multiplex RT-qPCR.

RESULTS

Of 300 participants, 150 had a RT-qPCR confirmed SARS-CoV-2 infection of whom 113 (75.33%) were also detected by the DiaSorin LIAISON SARS-CoV-2 Ag. Taking RT-qPCR as a reference, the sensitivity and specificity of the DiaSorin LIAISON SARS-CoV-2 Ag assay were evaluated as 75.33% (95% CI = 67.64-82) and 100% (95% CI = 97.57-100), respectively. When a viral load cut-off was applied for high viral load (median cycle threshold (Ct) < 18.57), the overall sensitivity was increased to 96.55% (95% CI = 88.09-99.58). Interestingly, median RT-qPCR Ct and SARS-CoV-2 Ag values were similar between fully vaccinated and unvaccinated subjects.

CONCLUSIONS

Automated, quantitative LIAISON SARS-CoV-2 Ag assay shows good performance to identify SARS-CoV-2-infected individuals with moderate to high viral loads. LIAISON SARS-CoV-2 Ag testing could be used as frontline testing for COVID-19 diagnosis and be more suitable for large utilization.

Evaluation of the Elecsys SARS-CoV-2 antigen assay for the detection of SARS-CoV-2 in nasopharyngeal swabs

Aims

The aim of this study was to evaluate the performance of the automated Elecsys® SARS-CoV-2 antigen assay compared to RT-PCR taken as the gold standard for SARS-CoV-2 detection.

Methods

225 nasopharyngeal swabs were randomly collected among which 123 were tested positive and 102 negatives for SARS-CoV-2 based on RT-PCR. Antigen dosing were performed on a Cobas 8000 e801 analyzer.

Results

The antigen test diagnosed SARS-CoV-2 infection status with an overall sensitivity of 65,85% (95% CI 56,76–74,16%), a specificity of 100% (95% CI 96,49–100%) with a Cut-off value ≥ 1. When the cut-off value for the antigen assay was set to > 0,673 COI, the accuracy reached its highest level with a sensitivity of 74,8% (95% CI 66,2 – 82,2%) and a specificity of 97,1% (95% CI 91,6 – 99,4%). Imprecision was estimated in accordance with manufacturer's claims.

Conclusions

We obtained an overall sensitivity of 65,85% (95% CI 56,76–74,16%) and a specificity of 100% (95% CI 96,49–100%), slightly higher than the results reported by the manufacturer. Yet, it remains relatively low comparatively to what is generally acceptable for these antigenic assays (a relative sensitivity of 80%). We also noticed that the accuracy could reach its highest level if the cut-off is set above 0,673 which is lower than established by the manufacturer. Thus, our results suggest that the Elecsys® SARS-CoV-2 Antigen assays, should be improved prior to be used in a SARS-Cov-2 screening strategy. However, if one antigenic assay could demonstrate acceptable performance, it might be centralized in clinical laboratories, keeping the RT-PCR in a second phase for confirmation.

A SARS-CoV-2 nucleocapsid ELISA represents a low-cost alternative to lateral flow testing for community screening in LMI countries

Background Controlling the spread of SARS-CoV-2 is problematic because of transmission driven by asymptomatic and pre-symptomatic individuals. Community screening can help identify these individuals but is often too expensive for countries with limited health care resources. Low-cost ELISA assays may address this problem, but their use has not yet been widely reported.

Methods We developed a SARS-CoV-2 nucleocapsid ELISA and assessed its diagnostic performance on nose and throat swab samples from UK hospitalised patients and sputum samples from patients in Ghana.

Results The ELISA had a limit of detection of 8.4 pg/ml antigen and 16 pfu/ml virus. When tested on UK samples (128 positive and 10 negative patients), sensitivity was 58.6% (49.6–67.2) rising to 78.3% (66.7–87.3) if real-time PCR Ct values > 30 were excluded, while specificity was 100% (69.2–100). In a second trial using the Ghanaian samples (121 positive, 96 negative), sensitivity was 52% (42.8–61.2) rising to 72.6% (61.8–81.2) when a > 30 Ct cut-off was applied, while specificity was 100% (96.2–100).

Conclusions: Our data show that nucleocapsid ELISAs can test a variety of patient sample types while achieving levels of sensitivity and specificity required for effective community screening. Further investigations into the opportunities that this provides are warranted.

Comparison of four commercial, automated antigen tests to detect SARS-CoV-2 variants of concern

A versatile portfolio of diagnostic tests is essential for the containment of the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) pandemic. Besides nucleic acid-based test systems and point-of-care (POCT) antigen (Ag) tests, quantitative, laboratory-based nucleocapsid Ag tests for SARS-CoV-2 have recently been launched. Here, we evaluated four commercial Ag tests on automated platforms and one POCT to detect SARS-CoV-2. We evaluated PCR-positive (n = 107) and PCR-negative (n = 303) respiratory swabs from asymptomatic and symptomatic patients at the end of the second pandemic wave in Germany (February–March 2021) as well as clinical isolates EU1 (B.1.117), variant of concern (VOC) Alpha (B.1.1.7) or Beta (B.1.351), which had been expanded in a biosafety level 3 laboratory. The specificities of automated SARS-CoV-2 Ag tests ranged between 97.0 and 99.7% (Lumipulse G SARS-CoV-2 Ag (Fujirebio): 97.03%, Elecsys SARS-CoV-2 Ag (Roche Diagnostics): 97.69%; LIAISON^® SARS-CoV-2 Ag (Diasorin) and SARS-CoV-2 Ag ELISA (Euroimmun): 99.67%). In this study cohort of hospitalized patients, the clinical sensitivities of tests were low, ranging from 17.76 to 52.34%, and analytical sensitivities ranged from 420,000 to 25,000,000 Geq/ml. In comparison, the detection limit of the Roche Rapid Ag Test (RAT) was 9,300,000 Geq/ml, detecting 23.58% of respiratory samples. Receiver-operating-characteristics (ROCs) and Youden’s index analyses were performed to further characterize the assays’ overall performance and determine optimal assay cutoffs for sensitivity and specificity. VOCs carrying up to four amino acid mutations in nucleocapsid were detected by all five assays with characteristics comparable to non-VOCs. In summary, automated, quantitative SARS-CoV-2 Ag tests show variable performance and are not necessarily superior to a standard POCT. The efficacy of any alternative testing strategies to complement nucleic acid-based assays must be carefully evaluated by independent laboratories prior to widespread implementation.

Accuracy of novel antigen rapid diagnostics for SARS-CoV-2: A living systematic review and meta-analysis

BACKGROUND

SARS-CoV-2 antigen rapid diagnostic tests (Ag-RDTs) are increasingly being integrated in testing strategies around the world. Studies of the Ag-RDTs have shown variable performance. In this systematic review and meta-analysis, we assessed the clinical accuracy (sensitivity and specificity) of commercially available Ag-RDTs.

METHODS AND FINDINGS

We registered the review on PROSPERO (registration number: CRD42020225140). We systematically searched multiple databases (PubMed, Web of Science Core Collection, medRvix, bioRvix, and FIND) for publications evaluating the accuracy of Ag-RDTs for SARS-CoV-2 up until 30 April 2021. Descriptive analyses of all studies were performed, and when more than 4 studies were available, a random-effects meta-analysis was used to estimate pooled sensitivity and specificity in comparison to reverse transcription polymerase chain reaction (RT-PCR) testing. We assessed heterogeneity by subgroup analyses, and rated study quality and risk of bias using the QUADAS-2 assessment tool. From a total of 14,254 articles, we included 133 analytical and clinical studies resulting in 214 clinical accuracy datasets with 112,323 samples. Across all meta-analyzed samples, the pooled Ag-RDT sensitivity and specificity were 71.2% (95% CI 68.2% to 74.0%) and 98.9% (95% CI 98.6% to 99.1%), respectively. Sensitivity increased to 76.3% (95% CI 73.1% to 79.2%) if analysis was restricted to studies that followed the Ag-RDT manufacturers' instructions. LumiraDx showed the highest sensitivity, with 88.2% (95% CI 59.0% to 97.5%). Of instrument-free Ag-RDTs, Standard Q nasal performed best, with 80.2% sensitivity (95% CI 70.3% to 87.4%). Across all Ag-RDTs, sensitivity was markedly better on samples with lower RT-PCR cycle threshold (Ct) values, i.e., <20 (96.5%, 95% CI 92.6% to 98.4%) and <25 (95.8%, 95% CI 92.3% to 97.8%), in comparison to those with Ct ≥ 25 (50.7%, 95% CI 35.6% to 65.8%) and ≥30 (20.9%, 95% CI 12.5% to 32.8%). Testing in the first week from symptom onset resulted in substantially higher sensitivity (83.8%, 95% CI 76.3% to 89.2%) compared to testing after 1 week (61.5%, 95% CI 52.2% to 70.0%). The best Ag-RDT sensitivity was found with anterior nasal sampling (75.5%, 95% CI 70.4% to 79.9%), in comparison to other sample types (e.g., nasopharyngeal, 71.6%, 95% CI 68.1% to 74.9%), although CIs were overlapping. Concerns of bias were raised across all datasets, and financial support from the manufacturer was reported in 24.1% of datasets. Our analysis was limited by the included studies' heterogeneity in design and reporting.

CONCLUSIONS

In this study we found that Ag-RDTs detect the vast majority of SARS-CoV-2-infected persons within the first week of symptom onset and those with high viral load. Thus, they can have high utility for diagnostic purposes in the early phase of disease, making them a valuable tool to fight the spread of SARS-CoV-2. Standardization in conduct and reporting of clinical accuracy studies would improve comparability and use of data.

Validation of a rapid antigen test as a screening tool for SARS-CoV-2 infection in asymptomatic populations. Sensitivity, specificity and predictive values

BACKGROUND

Early diagnosis of SARS-CoV-2 infection is essential to reduce disease spread. Rapid antigen tests have not been sufficiently evaluated in asymptomatic patients to be used as massive population screening tools.

METHODS

Head-to-head evaluation of Roche SARS-CoV-2 Rapid Antigen Test and real-time reverse transcription polymerase chain reaction (RT-PCR) as SARS-CoV-2 screening tools performed in asymptomatic adults from a semi-closed community in University of Navarra (Spain) from November 2020 to January 2021. Sensitivity, specificity and predictive values were calculated using RT-PCR as reference method.

FINDINGS

Roche SARS-CoV-2 Rapid Antigen Test was performed on 2542 asymptomatic adults in a community with a SARS-CoV-2 incidence of 1·93%. It showed a sensitivity of 71·43% (CI 95%: 56·74 - 83·42) and a specificity of 99·68% (CI 95%: 99·37 - 99·86). Positive Predictive Value was 81·4 (CI 95% 66·6 - 91·61) and Negative Predictive Value was 99·44 (CI 95% 99·06 - 99·69). Test sensitivity was related to viral load, with higher sensitivity in RT-PCR cycle threshold (Ct) values under 25 (93·75%, CI 95%: 71·96 - 98·93), that dropped to 29·41% (CI 95%: 10·31- 55·96) in RT-PCR Ct values above 25.

INTERPRETATION

This study suggests that rapid antigen tests are less effective in asymptomatic population, when compared with RT-PCR. Further studies are needed to evaluate different options to improve screenings based on rapid antigen test, such as the use of clinical questionnaires to select higher risk-participants, the confirmation of negative results with RT-PCR or the use of repetitive sequential testing.

FUNDING

This research received no external funding.

Clinical Assessment of the DiaSorin LIAISON SARS-CoV-2 Ag Chemiluminescence Immunoassay

BACKGROUND

Due to the large volume of tests needed in a relatively short time for screening and diagnosing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, antigen immunoassays may provide a potential supplement to molecular testing. This study was aimed to assess the clinical preference of DiaSorin LIAISON SARS-CoV-2 Ag chemiluminescence immunoassay.

METHODS

An upper respiratory specimen was collected in a series of patients referred to the Laboratory Medicine service of Pederzoli Hospital (Peschiera del Garda, Verona, Italy) for screening or diagnosis of SARS-CoV-2 infection. Nasopharyngeal samples were assayed with DiaSorin LIAISON SARS-CoV-2 Ag test and Altona Diagnostics RealStar^® SARS-CoV-2 RT-PCR Kit.

RESULTS

The final study population consisted of 421 patients (median age, 48 years; 227 women), 301 (71.5%) with positive result of molecular testing, and 126 (29.9%) with cycle threshold (Ct) values of both E and S genes <29.5, thus reflecting higher infectivity. The area under the curve of DiaSorin LIAISON SARS-CoV-2 Ag test 0.82 (95% CI, 0.79-0.86) for sample positivity and 0.98 for higher sample infectivity (95% CI, 0.97 to 0.99). The optimal cut-off for sample positivity was 82 TCID₅₀/mL (0.78 sensitivity, 0.73 specificity and 77% diagnostic accuracy), whilst that for identifying samples associated with a high infective risk was 106 TCID₅₀/mL (0.94 sensitivity, 0.96 specificity and 95% diagnostic accuracy).

CONCLUSION

The performance of this chemiluminescence immunoassay would not permit it to replace molecular testing for diagnosing SARS-CoV-2, but may enable rapid and efficient detection of subjects with high SARS-CoV-2 viral load, who are responsible for the largest proportion of infectious clusters.