Evaluation of the performance of multiple immunoassay diagnostic platforms on the National Microbiology Laboratory SARS-CoV-2 National Serology Panel.

BACKGROUND: Serological assays designed to detect SARS-CoV-2 antibodies are being used in serological surveys and other specialized applications. As a result, and to ensure that the outcomes of serological testing meet high quality standards, evaluations are required to assess the performance of these assays and the proficiency of laboratories performing them. METHODS: A panel of 60 plasma/serum samples from blood donors who had reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed SARS-CoV-2 infections and 21 SARS-CoV-2 negative samples were secured and distributed to interested laboratories within Canada (n = 30) and the United States (n = 1). Participating laboratories were asked to provide details on the diagnostic assays used, the platforms the assays were performed on, and the results obtained for each panel sample. Laboratories were blinded with respect to the expected outcomes. RESULTS: The performance of the different assays evaluated was excellent, with the high-throughput platforms of Roche, Ortho, and Siemens demonstrating 100% sensitivity. Most other high-throughput platforms had sensitivities of >93%, with the exception of the IgG assay using the Abbott ARCHITECT which had an average sensitivity of only 87%. The majority of the high-throughput platforms also demonstrated very good specificities (>97%). CONCLUSION: This proficiency study demonstrates that most of the SARS-CoV-2 serological assays utilized by provincial public health or hospital laboratories in Canada have acceptable sensitivity and excellent specificity.

HISTORIQUE: Les dosages sérologiques conçus pour dépister les anticorps anti-SRAS-CoV-2 sont utilisés dans les études sérologiques et d'autres applications spécialisées. Par conséquent, et pour s'assurer que leurs résultats respectent des normes de qualité, il faut procéder à des évaluations de leur performance et de la compétence des laboratoires à les effectuer. MÉTHODOLOGIE: Les chercheurs ont obtenu une batterie de 60 prélèvements de plasma et de sérum chez des donneurs dont l'amplification en chaîne par polymérase après transcription inverse (RT-PCR) avait confirmé des infections par le SRAS-CoV-2 et de 21 prélèvements dont les résultats étaient négatifs au SRAS-CoV-2 et les ont distribués aux laboratoires intéressés du Canada (n = 30) et des États-Unis (n = 1). Ils ont invité les laboratoires participants à fournir de l'information détaillée sur les dosages diagnostiques utilisés, les plateformes sur lesquelles les dosages étaient exécutés et les résultats obtenus pour chaque échantillon. Les chercheurs ont demandé aux laboratoires participants de fournir de l'information détaillée sur les dosages diagnostiques utilisés, les plateformes sur lesquelles les dosages ont été effectués, et les résultats obtenus à l'égard de chaque échantillon. Les laboratoires ont mené les études à l'insu des résultats escomptés. RÉSULTATS: Les divers dosages avaient une excellente exécution, les plateformes à haut débit de Roche, d'Ortho et de Siemens démontrant une sensibilité de 100 %. La plupart des autres plateformes à haut débit avaient des sensibilités de plus de 93 %, à l'exception des dosages des IgG faisant appel à l'analyseur ARCHITECT d'Abbott, dont la sensibilité moyenne était de seulement 87 %. La majorité des plateformes à haut débit avaient également une très bonne spécificité (plus de 97 %). CONCLUSION: La présente étude de compétence démontre que la plupart des dosages sérologiques du SRAS-CoV-2 évalués dans des laboratoires sanitaires provinciaux ou les laboratoires hospitaliers du Canada possèdent une sensibilité acceptable et une excellente spécificité.

Performance of Immunoglobulin G Serology on Finger Prick Capillary Dried Blood Spot Samples to Detect a SARS-CoV-2 Antibody Response.

We investigate the diagnostic accuracy and predictive value of finger prick capillary dried blood spot (DBS) samples tested by a quantitative multiplex anti-immunoglobulin G (IgG) assay to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies after infection or vaccination. This cross-sectional study involved participants (n = 6,841) from several serological surveys conducted in nonhospitalized children and adults throughout 2020 and 2021 in British Columbia (BC), Canada. Analysis used paired DBS and serum samples from a subset of participants (n = 642) prior to vaccination to establish signal thresholds and calculate diagnostic accuracy by logistic regression. Discrimination of the logistic regression model was assessed by receiver operator curve (ROC) analysis in an n = 2,000 bootstrap of the paired sample (n = 642). The model was cross-validated in a subset of vaccinated persons (n = 90). Unpaired DBS samples (n = 6,723) were used to evaluate anti-IgG signal distributions. In comparison to paired serum, DBS samples from an unvaccinated population possessed a sensitivity of 79% (95% confidence interval [95% CI]: 58 to 91%) and specificity of 97% (95% CI: 95 to 98%). ROC analysis found that DBS samples accurately classify SARS-CoV-2 seroconversion at an 88% percent rate (area under the curve [AUC] = 88% [95% CI: 80 to 95%]). In coronavirus disease 2019 (COVID-19) vaccine dose one or two recipients, the sensitivity of DBS testing increased to 97% (95% CI: 83 to 99%) and 100% (95% CI: 88 to 100%). Modeling found that DBS testing possesses a high positive predictive value (98% [95% CI: 97 to 98%]) in a population with 75% seroprevalence. We demonstrate that DBS testing should be considered to reliably detect SARS-CoV-2 seropositivity from natural infection or vaccination. IMPORTANCE Dried blood spot samples have comparable diagnostic accuracy to serum collected by venipuncture when tested by an electrochemiluminescent assay for antibodies and should be considered to reliably detect seropositivity following SARS-CoV-2 infection and/or vaccination.

Persistence of Anti-SARS-CoV-2 Antibodies in Long Term Care Residents Over Seven Months After Two COVID-19 Outbreaks.

Background: As part of the public health outbreak investigations, serological surveys were carried out following two COVID-19 outbreaks in April 2020 and October 2020 in one long term care facility (LTCF) in British Columbia, Canada. This study describes the serostatus of the LTCF residents and monitors changes in their humoral response to SARS-CoV-2 and other human coronaviruses (HCoV) over seven months. Methods: A total of 132 serum samples were collected from all 106 consenting residents (aged 54-102) post-first outbreak (N=87) and post-second outbreak (N=45) in one LTCF; 26/106 participants provided their serum following both COVID-19 outbreaks, permitting longitudinal comparisons between surveys. Health-Canada approved commercial serologic tests and a pan-coronavirus multiplexed immunoassay were used to evaluate antibody levels against the spike protein, nucleocapsid, and receptor binding domain (RBD) of SARS-CoV-2, as well as the spike proteins of HCoV-229E, HCoV-HKU1, HCoV-NL63, and HCoV-OC43. Statistical analyses were performed to describe the humoral response to SARS-CoV-2 among residents longitudinally. Findings: Survey findings demonstrated that among the 26 individuals that participated in both surveys, all 10 individuals seropositive after the first outbreak continued to be seropositive following the second outbreak, with no reinfections identified among them. SARS-CoV-2 attack rate in the second outbreak was lower (28.6%) than in the first outbreak (40.2%), though not statistically significant (P>0.05). Gradual waning of anti-nucleocapsid antibodies to SARS-CoV-2 was observed on commercial (median Δ=-3.7, P=0.0098) and multiplexed immunoassay (median Δ=-169579, P=0.014) platforms; however, anti-spike and anti-receptor binding domain (RBD) antibodies did not exhibit a statistically significant decline over 7 months. Elevated antibody levels for beta-HCoVs OC43 (P<0.0001) and HKU1 (P=0.0027) were observed among individuals seropositive for SARS-CoV-2 compared to seronegative individuals. Conclusion: Our study utilized well-validated serological platforms to demonstrate that humoral responses to SARS-CoV-2 persisted for at least 7 months. Elevated OC43 and HKU1 antibodies among SARS-CoV-2 seropositive individuals may be attributed to cross reaction and/or boosting of humoral response.

Performance comparison of micro-neutralization assays based on surrogate SARS-CoV-2 and WT SARS-CoV-2 in assessing virus-neutralizing capacity of anti-SARS-CoV-2 antibodies.

We compared neutralization assays using either the wild-type severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus or surrogate neutralization markers, using characterized sera. We found the results of the neutralization assays 75 % concordant overall and 80 % concordant for samples with high antibody levels. This demonstrates that commercial surrogate SARS-CoV-2 assays offer the potential to assess anti-SARS-CoV-2 antibodies' neutralizing capacity outside CL-3 laboratory containment.

Comparative Analysis of Capillary vs Venous Blood for Serologic Detection of SARS-CoV-2 Antibodies by RPOC Lateral Flow Tests.

A comparison of rapid point-of-care serology tests using finger prick and venous blood was done on 278 participants. In a laboratory setting, immunoglobulin G (IgG) sensitivity neared 100%; however, IgG sensitivity dramatically dropped (82%) in field testing. Possible factors include finger prick volume variability, hemolysis, cassette readability, and operator training.

Evaluation of a high volume antigen test for detection of SARS-CoV-2.

Increasing transmission of SARS-CoV-2 infection in successive waves may strain the capacity of laboratories performing molecular diagnostic testing. Alternative testing approaches may offer additional diagnostic capacity. A high throughput chemiluminescent antigen assay (Ortho VITROS SARS-CoV-2 antigen test) was evaluated using both an inactivated virus preparation and prospective clinical samples (nasopharyngeal swabs in virus transport medium). The limit of detection of the assay was approximately 0.5 TCID50/ml, equivalent to a Ct value of 33. The assay was linear over a wide range. When 528 clinical samples were tested with the antigen assay, the sensitivity was 84.2% and the specificity was 100% (positive predictive value 100% and negative predictive value 97.7%). High volume antigen tests might be used to supplement molecular diagnostic testing capacity.