Comparison of the analytical and clinical sensitivity of thirty-four rapid antigen tests with the most prevalent SARS-CoV-2 variants of concern during the COVID-19 pandemic in the UK (preprint)

Background The continued emergence of SARS-CoV-2 variants of concern (VOC) requires timely analytical and clinical evaluation of antigen-based rapid diagnostic tests (Ag-RDTs) especially those that are recommended for at home use. Methods The limit of detection (LOD) of 34 Ag-RDTs was evaluated using the most encountered SARS-CoV-2 VOC viral isolates (Alpha, Delta, Gamma, Omicron BA.1, Omicron BA.5) and the wild type (WT). Clinical sensitivity was further evaluated for five Ag-RDT utilising retrospective samples (Alpha, Delta, Omicron BA.1) and one Ag-RDT utilising prospective clinical samples (Delta and Omicron BA.1). Findings For the WT, Alpha, Delta, Gamma and Omicron (BA.1) variants 22, 32, 29, 31 and 32 of the 34 Ag-RDTs evaluated met the World Health Organisations (WHO) target product profile (TPP), respectively. Of the 31 Ag-RDTs included for Omicron BA.5 evaluation 29 met the WHO TPP. Additionally, the LODs for samples spiked with Omicron BA.5 were significantly lower than all other VOCs included (p<0.001). In the retrospective clinical evaluation when comparing RNA copies/mL, the Ag-RDTs detected Alpha and Omicron (BA.1) more sensitively than the Delta VOC. Samples with high RT-qPCR Cts (Ct>25) resulted in reduced test sensitivities across all variants. We used linear regression to model the 50% and 95% LOD of clinical samples and observed statistically similar results for all tests. In the prospective clinical samples, the sensitivity was statistically similar for the Delta VOC 71.9% (CI 95% 53.3-86.6%) and Omicron VOC 84.4% (CI95% 75.3-91.2%). Interpretation Test performance differs between SARS-CoV-2 VOCs, and high sensitivity was achieved when testing the Omicron BA.5 VOC compared to the WHO Ag-RDT requirements. Continuous evaluations must be performed to monitor test performance.

Diagnostic performance of lateral flow immunoassays for COVID-19 antibodies in Peruvian population (preprint)

Background Serological assays have been used in seroprevalence studies to inform the dynamics of COVID-19. Lateral flow immunoassay (LFIA) tests are a very practical technology to use for this objective; however, one of their challenges may be variable diagnostic performance. Given the numerous available LFIA tests, evaluation of their accuracy is critical before real-world implementation. Methods We performed a retrospective diagnostic evaluation study to independently determine the diagnostic accuracy of 4 different antibody-detection LFIA tests. The sample panel was comprised of specimens collected and stored in biobanks; specifically, specimens that were RT-PCR positive for SARS-CoV-2 collected at various times throughout the COVID-19 disease course and those that were collected before the pandemic, during 2018 or earlier, from individuals with upper respiratory symptoms but were negative for tuberculosis. Clinical performance (sensitivity and specificity) was analyzed overall, and subset across individual antibody isotypes, and days from symptoms onset. Results A very high specificity (98% - 100%) was found for all four tests. Overall sensitivity was variable, ranging from 29% [95% CI: 21%-39%] to 64% [95% CI: 54%-73%]. When considering detection of IgM only, the highest sensitivity was 42% [95% CI: 32%-52%], compared to 57% [95% CI: 47%-66%] for IgG only. When the analysis was restricted to at least 15 days since symptom onset, across any isotype, the sensitivity reached 90% for all four brands. Conclusion All four LFIA tests proved effective for identifying COVID-19 antibodies when two conditions were met: 1) at least 15 days have elapsed since symptom onset and 2) a sample is considered positive when either IgM or IgG is present. With these considerations, the use of this assays could help in seroprevalence studies or further exploration of its potential uses.

Impact of a multi-disease integrated screening and diagnostic model for COVID-19, TB, and HIV in Lesotho (preprint)

Introduction The surge of the COVID-19 pandemic challenged health services globally, and in Lesotho, the HIV and tuberculosis (TB) services were similarly affected. Integrated, multi-disease diagnostic services were proposed solutions to mitigate these disruptions. We describe and evaluate the effect of an integrated, hospital-based COVID-19, TB and HIV screening and diagnostic model in two rural districts in Lesotho, during the period between December 2020 and August 2022. Methods Adults and children above 5 years attending two hospitals were screened for COVID-19 and TB symptoms. After a positive screening, participants were offered to enroll in a service model that included clinical evaluation, chest radiography, SARS-CoV-2, Xpert MTB/RIF Ultra and HIV testing. Participants diagnosed with COVID-19, TB, or HIV were contacted after 28 days evaluate their health status, and linkage to HIV or TB services. Results Of the 179160 participants screened, 6623(37%) screened positive, and 4371(66%) were enrolled in this service model, yielding a total of 458 diagnoses. One positive rapid antigen test for SARS-CoV-2 was found per 11 participants screened, one Xpert-positive TB case was diagnosed per 85 people screened, and 1 new HIV diagnosis was done per 182 people screened. Of the 321(82.9%) participants contacted after 28 days of diagnosis, 304(94.7%) reported to be healthy. Of the individuals that were newly diagnosed with HIV or TB, 18/24(75.0%) and 46/51(90.1%) started treatment. This service showed no difference in the detection of new HIV and TB cases when compared to other hospitals, where no such integrated service model was provided. Conclusion This screening and diagnostic model successfully maintained same-day, integrated COVID-19, TB, and HIV testing services through different COVID-19 incidence periods in a resource-limited context. There were positive effects in avoiding diagnostic delays and ensuring linkage to services, however, efficiencies were contingent on the successful adaptation to the changing environment.

Multicentre diagnostic evaluation of OnSite COVID-19 Rapid Test (CTK Biotech) among symptomatic individuals in Brazil and The United Kingdom (preprint)

The COVID-19 pandemic has given rise to numerous commercially available antigen rapid diagnostic tests (Ag-RDTs). To generate and share accurate and independent data with the global community, multi-site prospective diagnostic evaluations of Ag-RDTs are required. This report describes the clinical evaluation of OnSite COVID-19 Rapid Test (CTK Biotech, California, USA) in Brazil and The United Kingdom. A total of 496 paired nasopharyngeal (NP) swabs were collected from symptomatic healthcare workers at Hospital das Clinicas in Sao Paulo, and 211 NP swabs were collected from symptomatic participants at a COVID-19 drive-through testing site in Liverpool, England. These swabs were analysed by Ag-RDT and results were compared to RT-qPCR. The overall clinical sensitivity of the OnSite COVID-19 Rapid test was 79.6% [95% Cl 70.8 - 86.8%] and specificity was 98.5% [95% Cl 97.2 - 99.3%]. Analytical evaluation of the Ag-RDT was assessed using direct culture supernatant of SARS-CoV-2 strains from Wild-Type (WT), Alpha, Delta, Gamma and Omicron lineages. Analytical limit of detection was 1.0x103 pfu/mL, 1.0x103 pfu/mL, 1.0x102 pfu/mL, 5.0x103 pfu/mL and 1.0x103 pfu/mL, giving a viral copy equivalent of approximately 2.1x105 copies/mL, 2.1x104 copies/mL, 1.6x104 copies/mL, 3.5x106 copies/mL and 8.7 x 104 for the Ag-RDT, when tested on the WT, Alpha, Delta, Gamma and Omicron lineages, respectively. Overall, the OnSite Ag-RDT demonstrates a lower clinical sensitivity than claimed by the manufacturers and narrowly missed out on the World Health Organization's minimum performance requirements for sensitivity of Ag-RDTs targeted to SARS-CoV-2. This study provides comparative performance of an Ag-RDT across two different settings, geographical areas, and population.

Analytical evaluation of thirty-two SARS-CoV-2 lateral flow antigen tests demonstrates sensitivity remains with the SARS-CoV-2 Gamma lineage (preprint)

The limit of detection (LOD) of thirty-two antigen lateral flow tests (Ag-RDT) were evaluated with the SARS-CoV-2 Gamma variant. Twenty-eight of thirty-two Ag-RDTs exceeded the World Health Organization criteria of an LOD of 1.0×10 6 genome copy numbers/ml and performance was equivalent as with the 2020 B.1 lineage and Alpha variant.

SARS-CoV-2 antibodies rapid tests: a valuable epidemiological tool in challenging settings (preprint)

Background During the last year, mass screening campaigns have been carried out to identify immunological response to SARS-CoV-2 and establish a possible seroprevalence. The obtained results gained new importance with the beginning of SARS-CoV-2 vaccination campaign, as the lack of doses has persuaded several countries to introduce different policies for individuals who had a history of COVID 19. LFAs may represent an affordable tool to support population screening in LMICs, where diagnostic tests are lacking, and epidemiology is still widely unknown. However, LFAs have demonstrated a wide range of performance and the question of which one could be more valuable in these settings still remains. Methods We evaluated the performance of 11 LFAs in detecting SARS-CoV-2 infection, analysing samples collected from 350 subjects. In addition, samples from 57 health care workers collected at 21-24 days after the first dose of Pfizer-BioNTech vaccine were also evaluated. Findings LFAs demonstrated a wide range of specificity (92.31% to 100%) and sensitivity (50 to 100%). The analysis of serum samples post vaccination was used to describe the most suitable tests to detect IgG response against S protein RBD. History of TB therapy was identified as a potential factor affecting the specificity of LFAs. Conclusions This analysis identified which LFAs represent a valuable tool not only for the detection of prior SARS-CoV-2 infection, but also to detect IgG elicited in response to vaccination. These results demonstrated that different LFAs may have different applications and the possible risks of their use in high TB burden settings.

Head-to-head performance comparison of self-collected nasal versus professional-collected nasopharyngeal swab for a WHO-listed SARS-CoV-2 antigen-detecting rapid diagnostic test (preprint)

BackgroundIn 2020, the World Health Organization (WHO) recommended two SARS-CoV-2 lateral flow antigen detecting rapid diagnostics tests (Ag-RDTs), both initially with nasopharyngeal (NP) sample collection. Independent head-to-head studies demonstrated for SARS-CoV-2 Ag-RDTs nasal sampling to be a comparable and reliable alternative for nasopharyngeal (NP) sampling. MethodsWe conducted a head-to-head comparison study of a supervised, self-collected nasal mid-turbinate (NMT) swab and a professional-collected NP swab, using the Panbio Ag-RDT (the second WHO-listed SARS-CoV-2 Ag-RDT, distributed by Abbott). We calculated positive and negative percent agreement and, compared to the reference standard reverse transcription polymerase chain reaction (RT-PCR), sensitivity and specificity for both sampling techniques. ResultsA SARS-CoV-2 infection could be diagnosed by RT-PCR in 45 of 290 participants (15.5%). Comparing the NMT and NP sampling the positive percent agreement of the Ag-RDT was 88.1% (37/42 PCR positives detected; CI 75.0% - 94.8%). The negative percent agreement was 98.8% (245/248; CI 96.5% - 99.6%). The overall sensitivity of Panbio with NMT sampling was 84.4% (38/45; CI 71.2% - 92.3%) and 88.9% (40/45; CI 76.5% - 95.5%) with NP sampling. Specificity was 99.2% (243/245; CI 97.1% - 99.8%) for both, NP and NMT sampling. The sensitivity of the Panbio test in participants with high viral load (> 7 log10 SARS-CoV-2 RNA copies/mL) was 96.3% (CI 81.7% - 99.8%) for both, NMT and NP sampling. ConclusionFor the Panbio Ag-RDT supervised NMT self-sampling yields to results comparable to NP sampling. This suggests that nasal self-sampling could be used for scale-up population testing.

Evaluation of accuracy, exclusivity, limit-of-detection and ease-of-use of LumiraDx™ - Antigen-detecting point-of-care device for SARS-CoV-2 (preprint)

BackgroundRapid antigen-detecting tests (Ag-RDTs) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can transform pandemic control. Thus far, sensitivity ([≤]85%) of lateral-flow assays has limited scale-up. Conceivably, microfluidic immunofluorescence Ag-RDTs could increase sensitivity for SARS-CoV-2 detection. Materials and MethodsThis multi-centre diagnostic accuracy study investigated performance of the microfluidic immunofluorescence LumiraDx assay, enrolling symptomatic and asymptomatic participants with suspected SARS-CoV-2 infection. Participants collected a supervised nasal mid-turbinate (NMT) self-swab for Ag-RDT testing, in addition to a professionally-collected nasopharyngeal (NP) swab for routine testing with reverse transcriptase polymerase chain reaction (RT-PCR). Results were compared to calculate sensitivity and specificity. Sub-analyses investigated the results by viral load, symptom presence and duration. An analytical study assessed exclusivity and limit-of-detection (LOD). In addition, we evaluated ease-of-use. ResultsStudy conduct was between November 2nd 2020 and January 21st 2021. 761 participants were enrolled, with 486 participants reporting symptoms on testing day. 120 out of 146 RT-PCR positive cases were detected positive by LumiraDx, resulting in a sensitivity of 82.2% (95% CI: 75.2%-87.5%). Specificity was 99.3% (CI: 98.3-99.7%). Sensitivity was increased in individuals with viral load [≥] 7 log10 SARS-CoV2 RNA copies/ml (93.8%; CI: 86.2%-97.3%). Testing against common respiratory commensals and pathogens showed no cross-reactivity and LOD was estimated to be 2-56 PFU/mL. The ease-of-use-assessment was favourable for lower throughput settings. ConclusionThe LumiraDx assay showed excellent analytical sensitivity, exclusivity and clinical specificity with good clinical sensitivity using supervised NMT self-sampling.

Diagnostic accuracy of PanbioTM rapid antigen tests on oropharyngeal swabs for detection of SARS-CoV-2 (preprint)

Background Antigen-detecting rapid diagnostic tests (Ag-RDTs) for the detection of SARS-CoV-2 offer new opportunities for testing in the context of the COVID-19 pandemic. Nasopharyngeal swabs (NPS) are the reference sample type, but oropharyngeal swabs (OPS) may be a more acceptable sample type in some patients. Methods We conducted a prospective study in a single screening center to assess the diagnostic performance of the PanbioTM COVID-19 Ag Rapid Test (Abbott) on OPS compared with reverse-transcription quantitative PCR (RT-qPCR) using NPS. Results 402 outpatients were enrolled in a COVID-19 screening center, of whom 168 (41.8%) had a positive RT-qPCR test. The oropharyngeal Ag-RDT sensitivity compared to nasopharyngeal RT-qPCR was 81% (95%CI: 74.2-86.6). Two false positives were noted out of the 234 RT-qPCR negative individuals, which resulted in a specificity of 99.1% (95%CI: 96.9-99.9) for the RDT. For cycle threshold values [≤] 26.7 ([≥] 1E6 SARS-CoV-2 genomes copies/mL, a presumed cut-off for infectious virus), 96.3% sensitivity (95%CI: 90.7-99.0%) was obtained with the Ag-RDT using OPS. Interpretation Based on our findings, the diagnostic performance of the PanbioTM Covid-19 RDT with OPS samples meet the criteria required by the WHO for Ag-RDTs (sensitivity [≥] 80% and specificity [≥] 97%).

Evaluation of the accuracy and ease-of-use of Abbott PanBio - A WHO emergency use listed, rapid, antigen-detecting point-of-care diagnostic test for SARS-CoV-2 (preprint)

BackgroundDiagnostics are essential for controlling the pandemic. Identifying a reliable and fast diagnostic is needed to support testing. We assessed performance and ease-of-use of the Abbott PanBio antigen-detecting rapid diagnostic test (Ag-RDT). MethodsThis prospective, multi-centre diagnostic accuracy study enrolled at two sites in Germany. Following routine testing with RT-PCR, a second study-exclusive swab was performed for Ag-RDT testing. Routine swabs were nasopharyngeal (NP) or combined NP/oropharyngeal (OP) whereas the study-exclusive swabs were NP. To evaluate performance, sensitivity and specificity were assessed overall and in predefined sub analyses accordingly to cycle-threshold values, days of symptoms, disease severity and study site. Additionally, an ease-of-use assessment and System Usability Scale (SUS) were performed. Findings1108 participants were enrolled between Sept 28 and Oct 30, 2020. Of these, 106 (9{middle dot}6%) were PCR-positive. The Abbott PanBio detected 92/106 PCR-positive participants with a sensitivity of 86{middle dot}8% (95% CI: 79{middle dot}0% - 92{middle dot}0%) and a specificity of 99{middle dot}9% (95% CI: 99{middle dot}4%-100%). The sub analyses indicated that sensitivity was 95{middle dot}8% in CT-values <25 and within the first seven days from symptom onset. The test was characterized as easy to use (SUS: 86/100) and considered suitable for point-of- care settings. InterpretationThe Abbott PanBio Ag-RDT performs well for SARS-CoV-2 testing in this large manufacturer independent study, confirming its WHO recommendation for Emergency Use in settings with limited resources. FundingThe Foundation of Innovative New Diagnostics supplied the test kits for the study. The internal funds from the Heidelberg University as well as the Charite Berlin supported this study.

Diagnostic accuracy of two commercial SARS-CoV-2 Antigen-detecting rapid tests at the point of care in community-based testing centers (preprint)

BackgroundAntigen-detecting rapid diagnostic tests for SARS-CoV-2 offer new opportunities for the quick and laboratory-independent identification of infected individuals for control of the SARS-CoV-2 pandemic. MethodsWe performed a prospective, single-center, point of care validation of two antigen-detecting rapid diagnostic tests (Ag-RDT) in comparison to RT-PCR on nasopharyngeal swabs. FindingsBetween October 9th and 23rd, 2020, 1064 participants were enrolled. The PanbioCovid-19 Ag Rapid Test device (Abbott) was validated in 535 participants, with 106 positive Ag-RDT results out of 124 positive RT-PCR individuals, yielding a sensitivity of 85.5% (95% CI: 78.0-91.2). Specificity was 100.0% (95% CI: 99.1-100) in 411 RT-PCR negative individuals. The Standard Q Ag-RDT (SD Biosensor, Roche) was validated in 529 participants, with 170 positive Ag-RDT results out of 191 positive RT-PCR individuals, yielding a sensitivity of 89.0% (95%CI: 83.7-93.1). One false positive result was obtained in 338 RT-PCR negative individuals, yielding a specificity of 99.7% (95%CI: 98.4-100). For individuals presenting with fever 1-5 days post symptom onset, combined Ag-RDT sensitivity was above 95%. InterpretationWe provide an independent validation of two widely available commercial Ag-RDTs, both meeting WHO criteria of [≥]80% sensitivity and [≥]97% specificity. Although less sensitive than RT-PCR, these assays could be beneficial due to their rapid results, ease of use, and independence from existing laboratory structures. Testing criteria focusing on patients with typical symptoms in their early symptomatic period onset could further increase diagnostic value. FundingFoundation of Innovative Diagnostics (FIND), Fondation privee des HUG, Pictet Charitable Foundation.