A novel strategy for SARS-CoV-2 mass screening with quantitative antigen testing of saliva: a diagnostic accuracy study

Pre-clinical and clinical evaluation of a surface plasmon field-enhanced fluorescence spectroscopy (SPFS) antigen test for detecting SARS-CoV-2

INTRODUCTION

The diagnostic tools of nucleic acid amplification tests and antigen tests have been extensively employed for the detection of Coronavirus disease 2019 (COVID-19). Although the reverse-transcriptase polymerase chain reaction (RT)-PCR test has high sensitivity and specificity, it is a time-consuming and labor-intensive process. On the other hand, antigen tests are simple and prompt, however, their low sensitivity and potential for false positives have been identified as limitations. In light of these factors, the development of novel tests that combine speed and clinical dependability is a promising prospect.

METHODS

Surface plasmon field-enhanced fluorescence spectroscopy (SPFS) excites chromophores by means of an enhanced electromagnetic field induced on a gold film surface. It enables the highly sensitive measurement of biomarkers in a short and simple 20-min window. In this study, a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) SPFS-based antigen test targeting the SARS-CoV-2 nucleocapsid protein was performed and evaluated in 25 patients with COVID-19 and 10 non-infected controls.

RESULTS

A positive correlation was observed between antigen levels determined by SPFS and RNA levels determined via RT-PCR. The sensitivity values were 100 %, 92 %, and 62.5 %; and the specificity values were 100 %, 90 %, and 100 %; for nasopharyngeal swabs, nasal swabs, and saliva specimens when the cutoff values were set to 65.1, 0.2, and 1.5 pg/mL, respectively. No clinically problematic cross-reactivity with analogous coronaviruses was observed.

CONCLUSIONS

The SARS-CoV-2 SPFS antigen test showed excellent clinical diagnostic accuracy for nasopharyngeal and nasal swabs, with a rapid turnaround.

A population-based study of the trend in SARS-CoV-2 diagnostic modalities from the beginning of the pandemic to the Omicron surge in Kyoto City, Kyoto, Japan

BACKGROUND

The coronavirus disease 2019 (COVID-19) presents critical diagnostic challenges for managing the pandemic. We investigated the 30-month changes in COVID-19 testing modalities and functional testing sites from the early period of the pandemic to the most recent Omicron surge in 2022 in Kyoto City, Japan.

METHODS

This is a retrospective-observational study using a local anonymized population database that included patients' demographic and clinical information, testing methods and facilities from January 2020 to June 2022, a total of 30 months. We computed the distribution of symptomatic presentation, testing methods, and testing facilities among cases. Differences over time were tested using chi-square tests of independence.

RESULTS

During the study period, 133,115 confirmed COVID-19 cases were reported, of which 90.9% were symptomatic. Although nucleic acid amplification testing occupied 68.9% of all testing, the ratio of lateral flow devices (LFDs) rapidly increased in 2022. As the pandemic continued, the testing capability was shifted from COVID-19 designated facilities to general practitioners, who became the leading testing providers (57.3% of 99,945 tests in 2022).

CONCLUSIONS

There was a dynamic shift in testing modality during the first 30 months of the pandemic in Kyoto City. General practitioners increased their role substantially as the use of LFDs spread dramatically in 2022. By comprehending and documenting the evolution of testing methods and testing locations, it is anticipated that this will contribute to the establishment of an even more efficient testing infrastructure for the next pandemic.

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.

Development and Characterization of Phage Display-Derived Monoclonal Antibodies to the S2 Domain of Spike Proteins of Wild-Type SARS-CoV-2 and Multiple Variants

The rapid emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants has resulted in the ongoing global coronavirus disease 2019 (COVID-19) pandemic. Thus, the rapid development of a platform to detect a broad range of SARS-CoV-2 variants is essential for successful COVID-19 management. In this study, four SARS-CoV-2 spike protein-specific single-chain variable fragments (scFvs) were isolated from a synthetic antibody library using phage display technology. Following the conversion of these scFvs into monoclonal antibodies (mAbs) (K104.1-K104.4) and production and purification of the mAbs, the antibody pair (K104.1 and K104.2) that exhibited the highest binding affinity (K104.1 and K104.2, 1.3 nM and 1.9 nM) was selected. Biochemical analyses revealed that this antibody pair specifically bound to different sites on the S2 subunit of the spike protein. Furthermore, we developed a highly sensitive sandwich immunoassay using this antibody pair that accurately and quantitatively detected the spike proteins of wild-type SARS-CoV-2 and multiple variants, including Alpha, Beta, Gamma, Delta, Kappa, and Omicron, in the picomolar range. Conclusively, the novel phage display-derived mAbs we have developed may be useful for the rapid and efficient detection of the fast-evolving SARS-CoV-2.

Investigation of the diagnostic performance of the SARS-CoV-2 saliva antigen test: A meta-analysis

BACKGROUND

The COVID-19 pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Rapid identification and isolation of patients with COVID-19 are critical strategies to contain COVID-19. The saliva antigen test has the advantages of noninvasiveness and decreased transmission risk to health-care professionals. This meta-analysis investigated the diagnostic accuracy of the saliva antigen test for SARS-CoV-2.

METHODS

We searched for relevant studies in PubMed, Embase, Cochrane Library, and Biomed Central. Studies evaluating the diagnostic accuracy of saliva antigen tests for SARS-CoV-2 were included. The data of the included studies were used to construct a 2 × 2 table on a per patient basis. The overall sensitivity and specificity of saliva antigen tests were determined using a bivariate random-effects model.

RESULTS

Nine studies enrolling 9842 patients were included. The meta-analysis generated a pooled sensitivity of 65.3% and a pooled specificity of 99.7%. A subgroup analysis of the studies performing the chemiluminescent enzyme immunoassay (CLEIA) for participants from airports and public health centers revealed a pooled sensitivity of 93.6%.

CONCLUSION

Our findings demonstrated that the saliva antigen test performed using CLEIA exhibited higher sensitivity for the detection of SARS-CoV-2. Therefore, the saliva antigen test performed using CLEIA might be an effective and noninvasive screening tool for SARS-CoV-2.

Saliva as a diagnostic specimen for SARS-CoV-2 detection: A scoping review

OBJECTIVES

This scoping review aims to summarize the diagnostic value of saliva assessed from current studies that (1) compare its performance in reverse transcriptase-polymerase chain reaction testing to nasopharyngeal swabs, (2) evaluate its performance in rapid and point-of-care COVID-19 diagnostic tests, and (3) explore its use as a specimen for detecting anti-SARS-CoV-2 antibodies.

MATERIALS AND METHODS

A systematic search was performed on the following databases: Medline and Embase (Ovid), World Health Organization, Centers for Disease Control and Prevention, and Global Health (Ovid) from January 2019 to September 2021. Of the 657 publications identified from the searches, n = 146 articles were included in the final scoping review.

RESULTS

Our findings showcase that salivary samples exceed nasopharyngeal swabs in detecting SARS-CoV-2 using reverse transcriptase-polymerase chain reaction testing in several studies. A select number of rapid antigen and point-of-care tests from the literature were also identified capable of high detection rates using saliva. Moreover, anti-SARS-CoV-2 antibodies have been shown to be detectable in saliva through biochemical assays.

CONCLUSION

We highlight the potential of saliva as an all-rounded specimen in detecting SARS-CoV-2. However, future large-scale clinical studies will be needed to support its widespread use as a non-invasive clinical specimen for COVID-19 testing.

SARS-CoV-2 Omicron detection by antigen tests using saliva

The Omicron emerged in November 2021 and became the predominant SARS-CoV-2 variant globally. It spreads more rapidly than ancestral lineages and its rapid detection is critical for the prevention of disease outbreaks. Antigen tests such as immunochromatographic assay (ICA) and chemiluminescent enzyme immunoassay (CLEIA) yield results more quickly than standard polymerase chain reaction (PCR). However, their utility for the detection of the Omicron variant remains unclear. We herein evaluated the performance of ICA and CLEIA in saliva from 51 patients with Omicron and 60 PCR negative individuals. The sensitivity and specificity of CLEIA were 98.0% (95%CI: 89.6-100.0%) and 100.0% (95%CI: 94.0-100.0%), respectively, with fine correlation with cycle threshold (Ct) values. The sensitivity and specificity of ICA were 58.8% (95%CI: 44.2-72.4%) and 100.0% (95%CI: 94.0-100.0%), respectively. The sensitivity of ICA was 100.0% (95%CI: 80.5-100.0%) when PCR Ct was less than 25. The Omicron can be efficiently detected in saliva by CLEIA. ICA also detects high viral load Omicron using saliva.

Potential usage of anterior nasal sampling in clinical practice with three rapid antigen tests for SARS-CoV-2

Introduction

Anterior nasal sampling (AN) might be more convenient for patients than NP sampling to diagnose coronavirus disease. This study investigated the feasibility of rapid antigen tests for AN sampling, and the factors affecting the test accuracy.

Methods

This single-center prospective study evaluated one qualitative (ESP) and two quantitative (LUMI and LUMI-P) rapid antigen tests using AN and NP swabs. Symptomatic patients aged 20 years or older, who were considered eligible for reverse-transcription quantitative polymerase chain reaction using NP samples within 9 days of onset were recruited. Sensitivity, specificity, and positive and negative concordance rates between AN and NP samples were assessed for the rapid antigen tests. We investigated the characteristics that affected the concordance between AN and NP sampling results.

Results

A total of 128 cases were recruited, including 28 positive samples and 96 negative samples. The sensitivity and specificity of AN samples using ESP were 0.81 and 1.00, while those of NP samples were 0.94 and 1.00. The sensitivity of AN and NP samples was 0.91 and 0.97, respectively, and specificity was 1.00, for both LUMI and LUMI-P. The positive concordance rates of AN to NP sampling were 0.87, 0.94, and 0.85 for ESP, LUMI, and LUMI-P, respectively. No factor had a significant effect on the concordance between the sampling methods.

Conclusions

ESP, LUMI, and LUMI-P showed practical diagnostic accuracy for AN sampling compared to NP sampling. There was no significant factor affecting the concordance between AN and NP sampling for these rapid antigen tests.

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.

Rapid Antigen Assays for SARS-CoV-2: Promise and Peril

Though rapid antigen tests have historically problematic performance characteristics for the diagnosis of respiratory viral infections such as influenza, they have attained an unprecedented level of use in the context of the COVID-19 pandemic. Ease of use and scalability of rapid antigen tests has facilitated a democratization and scale of testing beyond anything reasonably achievable by traditional laboratory-based testing. In this chapter, we discuss the performance characteristics of rapid antigen testing for SARS-CoV-2 detection and their application to non-traditional uses beyond clinical diagnostic testing.

Mass screening is a key component to fight against SARS-CoV-2 and return to normalcy

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had highly transmissible and pathogenic, which caused serious economic loss and hazard to public health. Different countries have developed strategies to deal with the COVID-19 pandemic that fit their epidemiological situations, capacities, and values. Mass screening combined with control measures rapidly reduced the transmission of the SARS-CoV-2 infection. The COVID-19 pandemic has dramatically highlighted the essential role of diagnostics capacity in the control of communicable diseases. Mass screening has been increasingly used to detect suspected COVID-19 cases and their close contacts, asymptomatic case, patients attending fever clinics, high-risk populations, employees, even all population to identify infectious individuals. Mass screening is a key component to fight against SARS-CoV-2 and return to normalcy. Here we describe the history of mass screening, define the scope of mass screening, describe its application scenarios, and discuss the impact and challenges of using this approach to control COVID-19. We conclude that through a comprehension screening program and strong testing capabilities, mass screening could help us return to normalcy more quickly.

Fujirebio Lumipulse SARS-CoV-2 antigen immunoassay: pooled analysis of diagnostic accuracy

We provide here a pooled analysis of accuracy of Fujirebio Lumipulse SARS-CoV-2 Antigen chemiluminescent immunoassay for diagnosing acute SARS-CoV-2 infections. An electronic search was conducted in Scopus and Medline with the keywords "Lumipulse" AND "antigen" AND "SARS-CoV-2" or "COVID-19", up to January 21, 2022, for identifying clinical investigations (minimum sample size ≥100) where diagnostic accuracy of Lumipulse G SARS-CoV-2 Ag was tested against reference molecular techniques. All studies which allowed to construct a 2 × 2 table were included in a pooled analysis. A final number of 21 studies, totalling 17,648 nasopharyngeal and 8538 saliva specimens, were finally included. The pooled diagnostic sensitivity and specificity in nasopharyngeal swabs were 0.80 (95%CI, 0.78-0.81) and 0.98 (95%CI, 0.97-0.98), respectively, whilst the area under the curve and agreement were 0.980 (95%CI, 0.973-0.986) and 94.9%, respectively. In the twelve studies which used the fixed 1.34 pg/mL currently recommended manufacturer's threshold, the diagnostic accuracy remained unvaried. In saliva samples, the pooled diagnostic sensitivity and specificity were 0.75 (95%CI, 0.36-0.62) and 1.00 (95%CI, 0.99-1.00), respectively, whilst the area under the curve and were 0.976 (95%CI, 0.969-0.984) and 98.4%, respectively. In the five studies which used the fixed 0.67 pg/mL currently recommended manufacturer's threshold, the diagnostic accuracy remained unvaried. In conclusion, Lumipulse G SARS-CoV-2 Ag assay demonstrates good diagnostic sensitivity and specificity, thus representing a valuable complementary and integrative option to molecular testing for SARS-CoV-2 in the current pandemic.

Severe Acute Respiratory Syndrome Coronavirus 2 Diagnostic Tests for Border Screening During the Very Early Phase of Coronavirus Disease 2019 Pandemic: A Systematic Review and Meta-Analysis

Diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during border screening among returning residents and prioritized travelers during the early phase of a pandemic can reduce the risk of importation and transmission in the community. This study aimed to compare the accuracy of various SARS-CoV-2 diagnostics and assess their potential utility as border screening for infection and immunity. Systematic literature searches were conducted in six electronic databases for studies reporting SARS-CoV-2 diagnostics (up to April 30, 2020). Meta-analysis and methodological assessment were conducted for all included studies. The performance of the diagnostic tests was evaluated with pooled sensitivity, specificity, and their respective 95% confidence intervals. A total of 5,416 unique studies were identified and 95 studies (at least 29,785 patients/samples) were included. Nucleic acid amplification tests (NAAT) consistently outperformed all other diagnostic methods regardless of the selected viral genes with a pooled sensitivity of 98% and a pooled specificity of 99%. Point-of-care (POC) serology tests had moderately high pooled sensitivity (69%), albeit lower than laboratory-based serology tests (89%), but both had high pooled specificity (96-98%). Serology tests were more sensitive for sampling collected at ≥ 7 days than ≤ 7 days from the disease symptoms onset. POC NAAT and POC serology tests are suitable for detecting infection and immunity against the virus, respectively as border screening. Independent validation in each country is highly encouraged with the preferred choice of diagnostic tool/s.

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.

Evaluation of a saliva molecular point of care for the detection of SARS-CoV-2 in ambulatory care

Rapid identification of SARS-CoV-2-infected individuals is a cornerstone for the control of virus spread. The sensitivity of SARS-CoV-2 RNA detection by RT-PCR is similar in saliva and nasopharyngeal swabs. Rapid molecular point-of-care tests in saliva could facilitate, broaden and speed up the diagnosis. We conducted a prospective study in two community COVID-19 screening centers to evaluate the performances of a CE-marked RT-LAMP assay (EasyCoV) designed for the detection of SARS-CoV2 RNA from fresh saliva samples, compared to nasopharyngeal RT-PCR, to saliva RT-PCR and to nasopharyngeal antigen testing. Overall, 117 of the 1718 participants (7%) tested positive with nasopharyngeal RT-PCR. Compared to nasopharyngeal RT-PCR, the sensitivity and specificity of the RT-LAMP assay in saliva were 34% and 97%, respectively. The Ct values of nasopharyngeal RT-PCR were significantly lower in the 40 true positive subjects with saliva RT-LAMP (Ct 25.9) than in the 48 false negative subjects with saliva RT-LAMP (Ct 28.4) (p = 0.028). Considering six alternate criteria for reference tests, including saliva RT-PCR and nasopharyngeal antigen, the sensitivity of saliva RT-LAMP ranged between 27 and 44%. The detection of SARS-CoV-2 in crude saliva samples with an RT-LAMP assay had a lower sensitivity than nasopharyngeal RT-PCR, saliva RT-PCR and nasopharyngeal antigen testing.Registration number: NCT04578509.

Performance of Qualitative and Quantitative Antigen Tests for SARS-CoV-2 Using Saliva

The rapid detection of SARS-CoV-2 is critical for the prevention of disease outbreaks. Antigen tests such as immunochromatographic assay (ICA) and chemiluminescent enzyme immunoassay (CLEIA) can yield results more quickly than PCR. We evaluated the performance of ICA and CLEIA using 34 frozen PCR-positive (17 saliva samples and 17 nasopharyngeal swabs [NPS]) and 309 PCR-negative samples. ICA detected SARS-CoV-2 in only 14 (41%) samples, with positivity rates of 24% in saliva and 59% in NPS. Notably, ICA detected SARS-CoV-2 in 5 of 6 samples collected within 4 days after symptom onset. CLEIA detected SARS-CoV-2 in 31 (91%) samples, with a positivity of 82% in saliva and 100% in NPS. These results suggest that the use of ICA should be limited to an earlier time after symptom onset and CLEIA is more sensitive and can be used in situations where quick results are required.

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.

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

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

Logistic advantage of two-step screening strategy for SARS-CoV-2 at airport quarantine

Background

Airport quarantine is required to reduce the risk of entry of travelers infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, it is challenging for both high accuracy and rapid turn-around time to coexist in testing; polymerase chain reaction (PCR) is time-consuming with high accuracy, while antigen testing is rapid with less accuracy. However, there are few data on the concordance between PCR and antigen testing.

Methods

Arrivals at three international airports in Japan between July 29 and September 30, 2020 were tested for SARS-CoV-2 using self-collected saliva by a screening strategy with initial chemiluminescent enzyme immunoassay (CLEIA) followed by confirmatory nucleic acid amplification tests (NAAT) only for intermediate range antigen concentrations.

Results

Among the 95,457 persons entering Japan during the period, 88,924 (93.2%) were tested by CLEIA, and 0.29% (254/88,924) were found to be SARS-CoV-2 antigen positive (≥4.0 pg/mL). NAAT was required for confirmatory testing in 0.58% (513/88,924) with intermediate antigen concentrations (0.67–4.0 pg/mL) whereby the virus was detected in 6.6% (34/513). This two-step strategy reduced the utilization of NAAT to one out of every 173 test subjects. The estimated performance of this strategy did not show significant increase in false negatives as compared to performing NAAT in all subjects.

Conclusions

Point of care testing by quantitative CLEIA using self-collected saliva is less labor-intensive and yields results rapidly, thus suitable as an initial screening test. Reserving NAAT for CLEIA indeterminate cases may prevent compromising accuracy while significantly improving the logistics of administering mass-screening at large venues.