Anterior nasal versus nasal mid-turbinate sampling for a SARS-CoV-2 antigen-detecting rapid test: does localisation or professional collection matter?

Rapid antigen testing for SARS-CoV-2 by lateral flow assay: A field evaluation of self- and professional testing at UK community testing sites

BACKGROUND

The advent of lateral flow devices (LFDs) for SARS-CoV-2 detection enabled widespread use of rapid self-tests during the pandemic. While self-testing using LFDs is now common, whether self-testing provides comparable performance to professional testing was a key question that remained important for pandemic planning.

METHODS

Three prospective multi-centre studies were conducted to compare the performance of self- and professional testing using LFDs. Participants tested themselves or were tested by trained (professional) testers at community testing sites in the UK. Corresponding qRT-PCR test results served as reference standard. The performance of Innova, Orient Gene and SureScreen LFDs by users (self) and professional testers was assessed in terms of sensitivity, specificity, and kit failure (void) rates. Impact of age, sex and symptom status was analysed using logistic regression modelling.

RESULTS

16,617 participants provided paired tests, of which 15,418 were included in the analysis. Self-testing with Innova, Orient Gene or SureScreen LFDs achieved sensitivities of 50 %, 53 % or 72 %, respectively, compared to qRT-PCR. Self and professional LFD testing showed no statistically different sensitivity with respect to corresponding qRT-PCR testing. Specificity was consistently equal to or higher than 99 %. Sex and age had no or only marginal impact on LFD performance while sensitivity was significantly higher for symptomatic individuals. Sensitivity of LFDs increased strongly to up to 90 % with higher levels of viral RNA measured by qRT-PCR.

CONCLUSIONS

Our results support SARS-CoV-2 self-testing with LFDs, especially for the detection of individuals whose qRT-PCR tests showed high viral concentrations.

Comparison of RT-PCR and antigen test sensitivity across nasopharyngeal, nares, and oropharyngeal swab, and saliva sample types during the SARS-CoV-2 omicron variant

Limited data highlight the need to understand differences in SARS-CoV-2 omicron (B.1.1.529) variant viral load between the gold standard nasopharyngeal (NP) swab, mid-turbinate (MT)/anterior nasal swabs, oropharyngeal (OP) swabs, and saliva. MT, OP, and saliva samples from symptomatic individuals in Atlanta, GA, in January 2022 and longitudinal samples from a small familial cohort were tested by both RT-PCR and ultrasensitive antigen assays. Higher concentrations in the nares were observed in the familial cohort, but a dominant sample type was not found among 39 cases in the cross-sectional cohort. The composite of positive MT or OP assay for both RT-PCR and antigen assay trended toward higher diagnostic yield but did not achieve significant difference. Our data did not identify a singular preferred sample type for SARS-CoV-2 testing, but higher levels of saliva nucleocapsid, a trend toward higher yield of composite OP/MT result, and association of apparent MT or OP predominance with symptoms warrant further study.

Self-administered versus clinician-performed BinaxNOW COVID rapid test: a comparison of accuracy

We conducted a single-center study at a free community testing site in Baltimore City to assess the accuracy of self-performed rapid antigen tests (RATs) for COVID-19. Self-administered BinaxNOW RATs were compared with clinician-performed RATs and against a reference lab molecular testing as the gold standard. Of the 953 participants, 14.9% were positive for SARS- CoV-2 as determined by RT-PCR. The sensitivity and specificity were similar for both self- and clinician-performed RATs (sensitivity: 83.9% vs 88.2%, P = 0.40; specificity: 99.8% vs 99.6%, P = 0.6). Subgroup comparisons based on age and race yielded similar results. Notably, 5.2% (95% CI: 1.5% to 9.5%) of positive results were potentially missed due to participant misinterpretation of the self-test card. However, the false-positive rate for RATs was reassuringly comparable in accuracy to clinician-administered tests. These findings hold significant implications for physicians prescribing treatment based on patient-reported, self-administered positive test results. Our study provides robust evidence supporting the reliability and utility of patient-performed RATs, underscoring their comparable accuracy to clinician-performed RATs, and endorsing their continued use in managing COVID-19. Further studies using other rapid antigen test brands are warranted.IMPORTANCEAccurate and accessible COVID-19 testing is crucial for effective disease control and management. A recent single-center study conducted in Baltimore City examined the reliability of self-performed rapid antigen tests (RATs) for COVID-19. The study found that self-administered RATs yielded similar sensitivity and specificity to clinician-performed tests, demonstrating their comparable accuracy. These findings hold significant implications for physicians relying on patient-reported positive test results for treatment decisions. The study provides robust evidence supporting the reliability and utility of patient-performed RATs, endorsing their continued use in managing COVID-19. Furthermore, the study highlights the need for further research using different rapid antigen test brands to enhance generalizability. Ensuring affordable and widespread access to self-tests is crucial, particularly in preparation for future respiratory virus seasons and potential waves of reinfection of SARS-CoV-2 variants such as the Omicron variant.

The potential for rapid antigen testing for mucormycosis in the context of COVID-19

INTRODUCTION

Mucormycosis is a highly aggressive angio-invasive disease of humans caused by Mucorales fungi. Prior to the COVID-19 pandemic, mucormycosis was a rare mycosis typically seen in immunocompromised patients with hematological malignancies or in transplant recipients. During the second wave of the pandemic, there was a dramatic increase in the disease, especially in India where a unique set of circumstances led to large numbers of life-threatening and disfiguring rhino-orbital-cerebral mucormycosis (ROCM) infections.

AREAS COVERED

The review examines mucormycosis as a super-infection of COVID-19 patients, and the risk factors for COVID-19-associated mucormycosis (CAM) that drove the ROCM epidemic in India. The limitations of current diagnostic procedures are identified, and the measures needed to improve the speed and accuracy of detection discussed.

EXPERT OPINION

Despite increased awareness, global healthcare systems remain unprepared for further outbreaks of ROCM. Current diagnosis of the disease is slow and inaccurate, negatively impacting on patient survival. This is most evident in low- to middle-income countries which lack suitably equipped diagnostic facilities for rapid identification of the infecting pathogens. Rapid antigen testing using point-of-care lateral-flow assays could potentially have aided in the quick and accurate diagnosis of the disease, allowing earlier intervention with surgery and Mucorales-active antifungal drugs.

Evaluation of COVID-19 antigen rapid diagnostic tests for self-testing in Lesotho and Zambia

INTRODUCTION

The use of antigen rapid tests (Ag-RDTs) for self-testing is an important element of the COVID-19 control strategy and has been widely supported. However, scale-up of self-testing for COVID-19 in sub-Saharan Africa is still insufficient and there is limited evidence on the acceptability of self-testing and agreement between Ag-RDT self-testing and Ag-RDT testing by professional users. A joint collaboration (Botnar Research Centre for Child Health-European & Developing countries Clinical Trials Partnership)was established between Lesotho and Zambia to address these gaps in relation to Ag-RDT self-testing and contribute to increasing its use in the region.

METHODS

A cross-sectional study was conducted with qualitative and quantitative data analysis. Firstly, 14 in-depth cognitive interviews (5 in Zambia and 9 in Lesotho) were performed to assess the participants' understanding of the instructions for use (IFU) for self-testing. In a second step, evaluation of test agreement between Ag-RDT self-testing and Ag-RDT testing by professional user using SD Biosensor STANDARD Q COVID-19 Ag-RDT was performed. In Zambia, usability and acceptability of self-testing were also assessed.

RESULTS

Cognitive interviews in Lesotho and Zambia showed overall good understanding of IFU. In Zambia, acceptability of self-testing was high, though some participants had difficulties in conducting certain steps in the IFU correctly. Agreement between Ag-RDT self-test and Ag-RDT by professional users in Lesotho (428 participants) and Zambia (1136 participants) was high, 97.3% (403/414, 95% CI: 95.3-98.7) and 99.8% (1116/1118, 95% CI: 99.4-100) respectively.

CONCLUSION

Findings from this study support the use of Ag-RDT self-testing within COVID-19 control strategies in sub-Saharan Africa, contributing to increase the testing capacity and access in hard-to reach settings.

Comparable performance of antigen-detecting rapid test by healthcare worker-collected and self-collected swabs for SARS-CoV-2 diagnostic: A systematic review and meta-analysis

Usage of self-screening tests has become increasingly relevant in public health perspective for early detection of SARS-CoV-2 infection in the transitioning era of the COVID-19 pandemic into an endemic. This study was designed to compare the diagnostic accuracy of self-conducted and health professional-conducted SARS-CoV-2 rapid antigen tests (Ag-RDTs) and whether the sample was taken from anterior nasal or nasal mid-turbinate. Eligible comparative Ag-RDTs accuracy studies were retrieved from electronic databases systematically, in accordance with PRISMA. Selected studies were assessed for risk of bias using QUADAS-2 and QUADAS-C. In total, we selected five out of 1952 studies retrieved using the keywords. The overall sensitivity for the self-collected nasal swab method and healthcare worker-collected nasopharyngeal swab method was 79% (95% CI 68-87; I2  = 62%) and 83% (95% CI 75-89; I2  = 32%), respectively, which was not statistically different (p = 0.499). Nasal mid-turbinate swabs have a significantly higher sensitivity compared to anterior nasal swabs (p < 0.01). Both sampling methods represent high and comparable specificity values of 98% (95% CI 97-99; I2  = 0%) and 99% (95% CI 98-99; I2  = 0%). Positive predictive value (range 90%-99%) and negative predictive value (range 87%-98%) were equivalent for both methods. Our findings indicated the accuracy of self-collected Ag-RDT on nasal swabs was comparable to those performed by healthcare worker-collected on nasopharyngeal swabs. Self-collected Ag-RDT could be considered as a transmission prevention method in the transition of COVID-19 pandemic.

Comparing SARS-CoV-2 antigen-detection rapid diagnostic tests for COVID-19 self-testing/self-sampling with molecular and professional-use tests: a systematic review and meta-analysis

Self-testing is an effective tool to bridge the testing gap for several infectious diseases; however, its performance in detecting SARS-CoV-2 using antigen-detection rapid diagnostic tests (Ag-RDTs) has not been systematically reviewed. This study aimed to inform WHO guidelines by evaluating the accuracy of COVID-19 self-testing and self-sampling coupled with professional Ag-RDT conduct and interpretation. Articles on this topic were searched until November 7th, 2022. Concordance between self-testing/self-sampling and fully professional-use Ag-RDTs was assessed using Cohen's kappa. Bivariate meta-analysis yielded pooled performance estimates. Quality and certainty of evidence were evaluated using QUADAS-2 and GRADE tools. Among 43 studies included, twelve reported on self-testing, and 31 assessed self-sampling only. Around 49.6% showed low risk of bias. Overall concordance with professional-use Ag-RDTs was high (kappa 0.91 [95% confidence interval (CI) 0.88-0.94]). Comparing self-testing/self-sampling to molecular testing, the pooled sensitivity and specificity were 70.5% (95% CI 64.3-76.0) and 99.4% (95% CI 99.1-99.6), respectively. Higher sensitivity (i.e., 93.6% [95% CI 90.4-96.8] for Ct < 25) was estimated in subgroups with higher viral loads using Ct values as a proxy. Despite high heterogeneity among studies, COVID-19 self-testing/self-sampling exhibits high concordance with professional-use Ag-RDTs. This suggests that self-testing/self-sampling can be offered as part of COVID-19 testing strategies.Trial registration: PROSPERO: CRD42021250706.

Diagnostic performance of rapid antigen tests for SARS-CoV-2 transmission risk based on cycle threshold values in the emergency department

BACKGROUND

This study aimed to investigate the diagnostic performance of the rapid antigen test (RAT) for screening patients with cycle threshold (Ct) values of SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) in the emergency department. Previous studies have shown that Ct values could be used as indicators of infectiousness. Therefore, we considered the Ct value an indicator of potential infectiousness.

METHODS

This single-center retrospective observational study was conducted between January 1, 2020, and March 31, 2022. Patients who underwent both RT-PCR and RAT for the diagnosis of COVID-19 were included. Patients with negative RT-PCR results were excluded. Patients with Ct values lower than 26 and 30 were considered potentially infectious for COVID-19.

RESULT

A total of 386 patients were analyzed. At Ct value cutoffs of 26 and 30, the result of the RAT showed a sensitivity of 82% and 74%, specificity of 84% and 89%, and area under the curve (AUC) of 0.829 and 0.813, respectively, in the receiver operating characteristic curve. However, the NPV was relatively low at 55% and 25%.

CONCLUSION

The RAT might be a rapid screening tool for detecting patients with the infectiousness of SARS-CoV-2. However, considering the low NPV, it is challenging to depend only on a negative test result from an antigen test to terminate quarantine. Clinicians should consider additional factors, such as the duration of symptoms and the immunocompromised state, for SARS-CoV-2 transmission.

Performance of different rapid antigen testing strategies for SARS-CoV-2: A living rapid review

BACKGROUND

Rapid antigen detection tests (RADTs) for SARS-CoV-2 testing offer several advantages over molecular tests, but there is little evidence supporting an ideal testing algorithm. We aimed to examine the diagnostic test accuracy (DTA) and the effectiveness of different RADT SARS-CoV-2 testing strategies.

METHODS

Following PRISMA DTA guidance, we carried out a living rapid review and meta-analysis. Searches were conducted in Ovid MEDLINE® ALL, Embase and Cochrane CENTRAL electronic databases until February 2022. Results were visualized using forest plots and included in random-effects univariate meta-analyses, where eligible.

RESULTS

After screening 8010 records, 18 studies were included. Only one study provided data on incidence outcomes. Seventeen studies were DTA reports with direct comparisons of RADT strategies, using RT-PCR as the reference standard. Testing settings varied, corresponding to original SARS-CoV-2 or early variants. Strategies included differences in serial testing, the individual collecting swabs and swab sample locations. Overall, specificity remained high (>98%) across strategies. Although results were heterogeneous, the sensitivity for healthcare worker-collected samples was greater than for self-collected samples. Nasal samples had comparable sensitivity when compared to paired RADTs with nasopharyngeal samples, but sensitivity was much lower for saliva samples. The limited evidence for serial testing suggested higher sensitivity if RADTs were administered every 3 days compared to less frequent testing.

CONCLUSIONS

Additional high-quality research is needed to confirm our findings; all studies were judged to be at risk of bias, with significant heterogeneity in sensitivity estimates. Evaluations of testing algorithms in real-world settings are recommended, especially for transmission and incidence outcomes.

The Infectious Diseases Society of America Guidelines on the Diagnosis of COVID-19: Antigen Testing

BACKGROUND

Immunoassays designed to detect SARS-CoV-2 protein antigens (Ag) are commonly used to diagnose COVID-19. The most widely used tests are lateral flow assays that generate results in approximately 15 minutes for diagnosis at the point-of-care. Higher throughput, laboratory-based SARS-CoV-2 Ag assays have also been developed. The number of commercially available SARS-CoV-2 Ag detection tests has increased rapidly, as has the COVID-19 diagnostic literature. The Infectious Diseases Society of America (IDSA) convened an expert panel to perform a systematic review of the literature and develop best practice guidance related to SARS-CoV-2 Ag testing. This guideline is an update to the third in a series of frequently updated COVID-19 diagnostic guidelines developed by the IDSA.

OBJECTIVE

The IDSA's goal was to develop evidence-based recommendations or suggestions that assist clinicians, clinical laboratories, patients, public health authorities, administrators and policymakers in decisions related to the optimal use of SARS-CoV-2 Ag tests in both medical and non-medical settings.

METHODS

A multidisciplinary panel of infectious diseases clinicians, clinical microbiologists and experts in systematic literature review identified and prioritized clinical questions related to the use of SARS-CoV-2 Ag tests. A review of relevant, peer-reviewed published literature was conducted through April 1, 2022. Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology was used to assess the certainty of evidence and make testing recommendations.

RESULTS

The panel made ten diagnostic recommendations. These recommendations address Ag testing in symptomatic and asymptomatic individuals and assess single versus repeat testing strategies.

CONCLUSIONS

U.S. Food and Drug Administration (FDA) SARS-CoV-2 Ag tests with Emergency Use Authorization (EUA) have high specificity and low to moderate sensitivity compared to nucleic acid amplification testing (NAAT). Ag test sensitivity is dependent on the presence or absence of symptoms, and in symptomatic patients, on timing of testing after symptom onset. In contrast, Ag tests have high specificity, and, in most cases, positive Ag results can be acted upon without confirmation. Results of point-of-care testing are comparable to those of laboratory-based testing, and observed or unobserved self-collection of specimens for testing yields similar results. Modeling suggests that repeat Ag testing increases sensitivity compared to testing once, but no empirical data were available to inform this question. Based on these observations, rapid RT-PCR or laboratory-based NAAT remains the testing method of choice for diagnosing SARS-CoV-2 infection. However, when timely molecular testing is not readily available or is logistically infeasible, Ag testing helps identify individuals with SARS-CoV-2 infection. Data were insufficient to make a recommendation about the utility of Ag testing to guide release of patients with COVID-19 from isolation. The overall quality of available evidence supporting use of Ag testing was graded as very low to moderate.

The Diagnostic Accuracy of SARS-CoV-2 Nasal Rapid Antigen Self-Test: A Systematic Review and Meta-Analysis

INTRODUCTION

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of coronavirus disease 2019 (COVID-19), a disease that quickly spread into a pandemic. As such, management of the COVID-19 pandemic is deemed necessary, and it can be achieved by using reliable diagnostic tests for SARS-CoV-2. The gold standard for the diagnosis of SARS-CoV-2 is a molecular detection test using the reverse transcription polymerase chain reaction technique (rt-PCR), which is characterized by various disadvantages in contrast with the self-taken nasal rapid antigen tests that produce results faster, have lower costs and do not require specialized personnel. Therefore, the usefulness of self-taken rapid antigen tests is indisputable in disease management, facilitating both the health system and the examinees. Our systematic review aims to access the diagnostic accuracy of the self-taken nasal rapid antigen tests.

METHODS

This systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool was used to assess the risk of bias in the included studies. All the studies included in this systematic review were found after searching the two databases, Scopus and PubΜed. All but original articles were excluded from this systematic review, while all the studies concerning self-taken rapid antigen tests with a nasal sample and using rt-PCR as a reference test were included. Meta-analysis results and plots were obtained using RevMan software and the MetaDTA website.

RESULTS

All 22 studies included in this meta-analysis demonstrated a specificity of self-taken rapid antigen tests greater than 98%, which exceeds the minimum required yield for the diagnosis of SARS-CoV-2, according to the WHO. Notwithstanding, the sensitivity varies (from 40% to 98.7%), which makes them in some cases unsuitable for the diagnosis of positive cases. In the majority of the studies, the minimum required performance set by the WHO was achieved, which is 80% compared with rt-PCR tests. The pooled sensitivity of self-taken nasal rapid antigen tests was calculated as 91.1% and the pooled specificity was 99.5%.

CONCLUSIONS

In conclusion, self-taken nasal rapid antigen tests have many advantages over rt-PCR tests, such as those related to the rapid reading of the results and their low cost. They also have considerable specificity and some self-taken rapid antigen test kits also have remarkable sensitivity. Consequently, self-taken rapid antigen tests have a wide range of utility but are not able to completely replace rt-PCR tests.

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.

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.

A prospective diagnostic evaluation of accuracy of self-taken and healthcare worker-taken swabs for rapid COVID-19 testing

BACKGROUND

Rapid diagnostic tests (RDTs) developed for point of care detection of SARS-CoV-2 antigen are recommended by WHO to use trained health care workers to collect samples. We hypothesised that self-taken samples are non-inferior for use with RDTs to diagnose COVID-19. We designed a prospective diagnostic evaluation comparing self-taken and healthcare worker (HCW)-taken throat/nasal swabs to perform RDTs for SARS-CoV-2, and how these compare to RT-PCR.

METHODS

Eligible participants 18 years or older with symptoms of COVID-19. 250 participants recruited at the NHS Test and Trace drive-through community PCR testing site (Liverpool, UK); one withdrew before analysis. Self-administered throat/nasal swab for the Covios® RDT, a trained HCW taken throat/nasal sample for PCR and HCW comparison throat/nasal swab for RDT were collected. RDT results were compared to RT-PCR, as the reference standard, to calculate sensitivity and specificity.

FINDINGS

Seventy-five participants (75/249, 30.1%) were positive by RT-PCR. RDTs with self-taken swabs had a sensitivity of 90.5% (67/74, 95% CI: 83.9-97.2), compared to 78.4% (58/74, 95% CI: 69.0-87.8) for HCW-taken swabs (absolute difference 12.2%, 95% CI: 4.7-19.6, p = 0.003). Specificity for self-taken swabs was 99.4% (173/174, 95% CI: 98.3-100.0), versus 98.9% (172/174, 95% CI: 97.3-100.0) for HCW-taken swabs (absolute difference 0.6%, 95% CI: 0.5-1.7, p = 0.317). The PPV of self-taken RDTs (98.5%, 67/68, 95% CI: 95.7-100.0) and HCW-taken RDTs (96.7%, 58/60, 95% CI 92.1-100.0) were not significantly different (p = 0.262). However, the NPV of self-taken swab RDTs was significantly higher (96.1%, 173/180, 95% CI: 93.2-98.9) than HCW-taken RDTs (91.5%, 172/188, 95% CI 87.5-95.5, p = 0.003).

INTERPRETATION

In conclusion, self-taken swabs for COVID-19 testing offer an accurate alternative to healthcare worker taken swabs for use with RDTs. Our results demonstrate that, with no training, self-taken throat/nasal samples can be used by lay individuals as part of rapid testing programmes for symptomatic adults. This is especially important where the lack of trained healthcare workers restricts access to testing.

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.

ESCMID COVID-19 guidelines: diagnostic testing for SARS-CoV-2

SCOPE

The objective of these guidelines is to identify the most appropriate diagnostic test and/or diagnostic approach for SARS-CoV-2. The recommendations are intended to provide guidance to clinicians, clinical microbiologists, other health care personnel, and decision makers.

METHODS

An ESCMID COVID-19 guidelines task force was established by the ESCMID Executive Committee. A small group was established, half appointed by the chair and the remaining selected with an open call. Each panel met virtually once a week. For all decisions, a simple majority vote was used. A list of clinical questions using the PICO (population, intervention, comparison, outcome) format was developed at the beginning of the process. For each PICO, two panel members performed a literature search focusing on systematic reviews, with a third panellist involved in case of inconsistent results. Quality of evidence assessment was based on the GRADE-ADOLOPMENT (Grading of Recommendations Assessment, Development and Evaluation - adoption, adaptation, and de novo development of recommendations) approach.

RECOMMENDATIONS

A total of 43 PICO questions were selected that involve the following types of populations: (a) patients with signs and symptoms of COVID-19; (b) travellers, healthcare workers, and other individuals at risk for exposure to SARS-CoV-2; (c) asymptomatic individuals, and (d) close contacts of patients infected with SARS-CoV-2. The type of diagnostic test (commercial rapid nucleic acid amplification tests and rapid antigen detection), biomaterial, time since onset of symptoms/contact with an infectious case, age, disease severity, and risk of developing severe disease are also taken into consideration.

Accuracy of rapid point-of-care antigen-based diagnostics for SARS-CoV-2: An updated systematic review and meta-analysis with meta-regression analyzing influencing factors

BACKGROUND

Comprehensive information about the accuracy of antigen rapid diagnostic tests (Ag-RDTs) for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is essential to guide public health decision makers in choosing the best tests and testing policies. In August 2021, we published a systematic review and meta-analysis about the accuracy of Ag-RDTs. We now update this work and analyze the factors influencing test sensitivity in further detail.

METHODS AND FINDINGS

We registered the review on PROSPERO (registration number: CRD42020225140). We systematically searched preprint and peer-reviewed databases for publications evaluating the accuracy of Ag-RDTs for SARS-CoV-2 until August 31, 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 with reverse transcription polymerase chain reaction (RT-PCR) testing as a reference. To evaluate factors influencing test sensitivity, we performed 3 different analyses using multivariable mixed-effects meta-regression models. We included 194 studies with 221,878 Ag-RDTs performed. Overall, the pooled estimates of Ag-RDT sensitivity and specificity were 72.0% (95% confidence interval [CI] 69.8 to 74.2) and 98.9% (95% CI 98.6 to 99.1). When manufacturer instructions were followed, sensitivity increased to 76.3% (95% CI 73.7 to 78.7). Sensitivity was markedly better on samples with lower RT-PCR cycle threshold (Ct) values (97.9% [95% CI 96.9 to 98.9] and 90.6% [95% CI 88.3 to 93.0] for Ct-values <20 and <25, compared to 54.4% [95% CI 47.3 to 61.5] and 18.7% [95% CI 13.9 to 23.4] for Ct-values ≥25 and ≥30) and was estimated to increase by 2.9 percentage points (95% CI 1.7 to 4.0) for every unit decrease in mean Ct-value when adjusting for testing procedure and patients' symptom status. Concordantly, we found the mean Ct-value to be lower for true positive (22.2 [95% CI 21.5 to 22.8]) compared to false negative (30.4 [95% CI 29.7 to 31.1]) results. Testing in the first week from symptom onset resulted in substantially higher sensitivity (81.9% [95% CI 77.7 to 85.5]) compared to testing after 1 week (51.8%, 95% CI 41.5 to 61.9). Similarly, sensitivity was higher in symptomatic (76.2% [95% CI 73.3 to 78.9]) compared to asymptomatic (56.8% [95% CI 50.9 to 62.4]) persons. However, both effects were mainly driven by the Ct-value of the sample. With regards to sample type, highest sensitivity was found for nasopharyngeal (NP) and combined NP/oropharyngeal samples (70.8% [95% CI 68.3 to 73.2]), as well as in anterior nasal/mid-turbinate samples (77.3% [95% CI 73.0 to 81.0]). Our analysis was limited by the included studies' heterogeneity in viral load assessment and sample origination.

CONCLUSIONS

Ag-RDTs detect most of the individuals infected with SARS-CoV-2, and almost all (>90%) when high viral loads are present. With viral load, as estimated by Ct-value, being the most influential factor on their sensitivity, they are especially useful to detect persons with high viral load who are most likely to transmit the virus. To further quantify the effects of other factors influencing test sensitivity, standardization of clinical accuracy studies and access to patient level Ct-values and duration of symptoms are needed.

Comparison between Nasal and Nasopharyngeal Swabs for SARS-CoV-2 Rapid Antigen Detection in an Asymptomatic Population, and Direct Confirmation by RT-PCR from the Residual Buffer

Containment measures employed during the COVID-19 pandemic included prompt recognition of cases, isolation, and contact tracing. Bilateral nasal (NA) swabs applied to a commercial antigen-based rapid diagnostic test (Ag-RDT) offer a simpler and more comfortable alternative to nasopharyngeal (NP) collection; however, little is known about the sensitivity of this method in an asymptomatic population. Participants in community-based asymptomatic testing sites were screened for SARS-CoV-2 using an Ag-RDT with NP sampling. Positive individuals returned for confirmatory molecular testing and consented to repeating the Ag-RDT using a bilateral NA swab for comparison. Residual test buffer (RTB) from Ag-RDTs was subjected to real-time reverse transcription-PCR (RT-PCR). Of 123,617 asymptomatic individuals, 197 NP Ag-RDT-positive participants were included, with 175 confirmed positive by RT-PCR. Of these cases, 154 were identified from the NA swab collection with Ag-RDT, with a sensitivity of 88.0% compared to the NP swab collection. Stratifying results by RT-PCR cycle threshold demonstrated that sensitivity of the nasal collection method varied based on the cycle threshold (C_T) value of the paired RT-PCR sample. RT-PCR testing on the RTB from the Ag-RDT using NP and NA swab collections resulted in 100.0% and 98.7% sensitivity, respectively. NA swabs provide an adequate alternative to NP swab collection for use with Ag-RDT, with the recognition that the test is most sensitive in specimens with high viral loads. With the high sensitivity of RT-PCR testing on RTB from Ag-RDT, a more streamlined approach to confirmatory testing is possible without recollection or use of paired collections strategies.

IMPORTANCE Nasal swabbing for SARS-CoV-2 (COVID-19) comes with many benefits but is slightly less sensitive than traditional nasopharyngeal swabbing; however, confirmatory lab-based testing could be performed directly from the residual buffer from either sample type.

Where is Omicron? Comparison of SARS-CoV-2 RT-PCR and Antigen Test Sensitivity at Commonly Sampled Anatomic Sites Over the Course of Disease

BACKGROUND

Upper respiratory samples for SARS-CoV-2 detection include the gold standard nasopharyngeal (NP) swab, and mid-turbinate (MT) nasal swabs, oropharyngeal (OP) swabs, and saliva. Following the emergence of the omicron (B.1.1.529) variant, limited preliminary data suggest that OP swabs or saliva samples may be more sensitive than nasal swabs, highlighting the need to understand differences in viral load across different sites.

METHODS

MT, OP, and saliva samples were collected from symptomatic individuals presenting for evaluation in Atlanta, GA, in January 2022. Longitudinal samples were collected from a family cohort following COVID-19 exposure to describe detection of viral targets over the course of infection.

RESULTS

SARS-CoV-2 RNA and nucleocapsid antigen measurements demonstrated a nares-predominant phenotype in a familial cohort. A consistent dominant location for SARS-CoV-2 was not found among 54 individuals. Positive percent agreement for virus detection in MT, OP and saliva specimens were 66.7 [54.1-79.2], 82.2 [71.1-93.4], and 72.5 [60.3-84.8] by RT-PCR, respectively, and 46.2 [32.6-59.7], 51.2 [36.2-66.1], and 72.0 [59.6-84.4] by ultrasensitive antigen assay. The composite of positive MT or OP assay was not significantly different than either alone for both RT-PCR and antigen assay (PPA 86.7 [76.7-96.6] and 59.5 [44.7-74.4], respectively).

CONCLUSIONS

Our data suggest that SARS-CoV-2 nucleocapsid and RNA exhibited similar kinetics and diagnostic yield in three upper respiratory sample types across the duration of symptomatic disease. Collection of OP or combined nasal and OP samples does not appear to increase sensitivity versus validated nasal sampling for rapid detection of viral antigen.

Development of a risk assessment profile tool to determine appropriate use of SARS-CoV-2 rapid antigen detection tests for different activities and events in Ireland, since October 2021

We describe the development of a risk assessment profile tool that incorporates data from multiple domains to help determine activities and events where rapid antigen detection tests (Ag-RDT) could be used to screen asymptomatic individuals to identify infectious cases as an additional mitigation measure to reduce transmission of SARS-CoV-2. The tool aims to stratify, in real time, the overall risk of SARS-CoV-2 transmission associated with common activities and events, and this can be matched to an appropriate Ag-RDT testing protocol.

Clinical evaluation of the SD Biosensor SARS-CoV-2 saliva antigen rapid test with symptomatic and asymptomatic, non-hospitalized patients

BACKGROUND

Performance of the SD Biosensor saliva antigen rapid test was evaluated at a large designated testing site in non-hospitalized patients, with or without symptoms.

METHOD

All eligible people over 18 years of age presenting for a booked appointment at the designated SARS-CoV-2 testing site were approached for inclusion and enrolled following verbal informed consent. One nasopharyngeal swab was taken to carry out the default antigen rapid test from which the results were reported back to the patient and one saliva sample was self-taken according to verbal instruction on site. This was used for the saliva antigen rapid test, the RT-PCR and for virus culture. Sensitivity of the saliva antigen rapid test was analyzed in two ways: i, compared to saliva RT-PCR; and ii, compared to virus culture of the saliva samples. Study participants were also asked to fill in a short questionnaire stating age, sex, date of symptom onset. Recommended time of ≥30mins since last meal, drink or cigarette if applicable was also recorded. The study was carried out in February-March 2021 for 4 weeks.

RESULTS

We could include 789 people with complete records and results. Compared to saliva RT-PCR, overall sensitivity and specificity of the saliva antigen rapid test was 66.1% and 99.6% which increased to 88.6% with Ct ≤30 cutoff. Analysis by days post onset did not result in higher sensitivities because the large majority of people were in the very early phase of disease ie <3 days post onset. When breaking down the data for symptomatic and asymptomatic individuals, sensitivity ranged from 69.2% to 50% respectively, however the total number of RT-PCR positive asymptomatic participants was very low (n = 5). Importantly, almost all culture positive samples were detected by the rapid test.

CONCLUSION

Overall, the potential benefits of saliva antigen rapid test, could outweigh the lower sensitivity compared to nasopharyngeal antigen rapid test in a comprehensive testing strategy, especially for home/self-testing and in vulnerable populations like elderly, disabled or children where in intrusive testing is either not possible or causes unnecessary stress.

Evaluation of the Practicability of Biosynex Antigen Self-Test COVID-19 AG+ for the Detection of SARS-CoV-2 Nucleocapsid Protein from Self-Collected Nasal Mid-Turbinate Secretions in the General Public in France

Due to their ease-of-use, lateral flow assay SARS-CoV-2 antigen-detecting rapid diagnostic tests could be suitable candidates for antigen-detecting rapid diagnostic self-test (Ag-RDST). We evaluated the practicability of the Ag-RDST BIOSYNEX Antigen Self-Test COVID-19 Ag+ (Biosynex Swiss SA, Freiburg, Switzerland), using self-collected nasal secretions from the turbinate medium (NMT), in 106 prospectively included adult volunteers living in Paris, France. The majority of the participants correctly understood the instructions for use (94.4%; 95% confidence interval (CI): 88.3-97.4), showing a great ability to perform the entire self-test procedure to obtain a valid and interpretable result (100%; 95% CI: 96.5-100), and demonstrated the ability to correctly interpret test results (96.2%; 95% CI: 94.2-97.5) with a high level of general satisfaction. About one in eight participants (# 15%) needed verbal help to perform or interpret the test, and only 3.8% of test results were misinterpreted. By reference to multiplex real-time RT-PCR, the Ag-RDST showed 90.9% and 100% sensitivity and specificity, respectively, and high agreement (98.1%), reliability (0.94), and accuracy (90.9%) to detect SARS-CoV-2 antigen. Taken together, our study demonstrates the high usability and accuracy of BIOSYNEX Antigen Self-Test COVID-19 Ag+ for supervised self-collected NMT sampling in an unselected adult population living in France.

Performance of Seven SARS-CoV-2 Self-Tests Based on Saliva, Anterior Nasal and Nasopharyngeal Swabs Corrected for Infectiousness in Real-Life Conditions: A Cross-Sectional Test Accuracy Study

Many studies reported good performance of nasopharyngeal swab-based antigen tests for detecting SARS-CoV-2-positive individuals; however, studies independently evaluating the quality of antigen tests utilizing anterior nasal swabs or saliva swabs are still rare, although such tests are widely used for mass testing. In our study, sensitivities, specificities and predictive values of seven antigen tests for detection of SARS-CoV-2 (one using nasopharyngeal swabs, two using anterior nasal swabs and four using saliva) were evaluated. In a setting of a high-capacity testing center, nasopharyngeal swabs for quantitative PCR (qPCR) were taken and, at the same time, antigen testing was performed in accordance with manufacturers' instructions for the respective tests. In samples where qPCR and antigen tests yielded different results, virus culture was performed to evaluate the presence of the viable virus. Sensitivities and specificities of individual tests were calculated using both qPCR and qPCR corrected for viability as the reference. In addition, calculations were also performed for data categorized according to the cycle threshold and symptomatic status. The test using nasopharyngeal swabs yielded the best results (sensitivity of 80.6% relative to PCR and 91.2% when corrected for viability) while none of the remaining tests (anterior nasal swab or saliva-based tests) came even close to the WHO criteria for overall sensitivity. Hence, we advise caution when using antigen tests with alternative sampling methods without independent validation.