Anti-N SARS-CoV-2 assays for evaluation of natural viral infection.

BACKGROUND: The 2019 coronavirus (COVID-19) epidemic, required the development of different diagnostic tests. While reverse transcriptase real-time PCR (RT-PCR) remains the first-line test of choice in acute infection diagnosis, anti-N antibodies serological assays provide a valuable tool to differentiate natural SARS-CoV-2 immunological response from that induced by vaccination, thus the goal of our study was to evaluate three serological tests agreement for these antibodies detection. METHODS: Three anti-N different tests were examined in 74 sera from patients referred or not COVID infection: immunochromatographic rapid test (Panbio™ COVID-19 IgG/IgM Rapid Test Device Abbott, Germany), ELISA kit (NovaLisa® SARS-CoV-2 IgG and IgM NovaTech Immunodiagnostic GmbH, Germany) and ECLIA immunoassay (Elecsys® Anti-SARS-CoV-2 Roche Diagnostics, Manheim, Germany). RESULTS: Qualitative comparison of the three analytical methods revealed a moderate agreement between ECLIA immunoassay and immunochromatographic rapid test (Cohen kappa coefficient κ = 0.564). Correlation analysis indicated weak positive correlation between total Ig (IgT) detected by ECLIA immunoassay and IgG by ELISA test (p < 0.0001), the analysis of ECLIA IgT and IgM ELISA detected, showed no statistical correlation. CONCLUSION: Comparison between of three analytical systems available for anti-N SARS-CoV-2 IgG and IgM antibodies showed a general agreement when compared to detect total and G class immunoglobulins, while doubtful or discordant results have been highlighted for IgT and IgM class. Anyway, all the tests examined provide reliable results to assess the serological status of SARS-CoV-2 infected patients.

Sensitivity of SARS-CoV-2 antibody tests with late convalescent sera.

SARS-CoV-2-specific IgM antibodies wane during the first three months after infection and IgG antibody levels decline. This may limit the ability of antibody tests to identify previous SARS-CoV-2 infection at later time points. To examine if the diagnostic sensitivity of antibody tests falls off, we compared the sensitivity of two nucleoprotein-based antibody tests, the Roche Elecsis II Anti-SARS-CoV-2 and the Abbott SARS-CoV-2 IgG assay and three glycoprotein-based tests, the Abbott SARS-CoV-2 IgG II Quant, Siemens Atellica IM COV2T and Euroimmun SARS-CoV-2 assay with 53 sera obtained 6 months after SARS-CoV-2 infection. The sensitivity of the Roche, Abbott SARS-CoV-2 IgG II Quant and Siemens antibody assays was 94.3% (95% confidence interval (CI) 84.3-98.8%), 98.1 % (95% CI: 89.9-100%) and 100 % (95% CI: 93.3-100%). The sensitivity of the N-based Abbott SARS-CoV-2 IgG and the glycoprotein-based Euroimmun ELISA was 45.3 % (95% CI: 31.6-59.6%) and 83.3% (95% CI: 70.2-91.9%). The nucleoprotein-based Roche and the glycoprotein-based Abbott receptor binding domain (RBD) and Siemens tests were more sensitive than the N-based Abbott and the Euroimmun antibody tests (p = 0.0001 to p = 0.039). The N-based Abbott antibody test was less sensitive 6 months than 4-10 weeks after SARS-CoV-2 infection (p = 0.0001). The findings show that most SARS-CoV-2 antibody assays correctly identified previous infection 6 months after infection. The sensitivity of pan-Ig antibody tests was not reduced at 6 months when IgM antibodies have usually disappeared. However, one of the nucleoprotein-based antibody tests significantly lost diagnostic sensitivity over time.

Validation of a SARS-CoV-2 Surrogate Virus Neutralization Test in Recovered and Vaccinated Healthcare Workers.

Vaccination against COVID-19 is the main public health approach to fight against the pandemic. The Spike (S) glycoprotein of SARS-CoV-2 is the principal target of the neutralizing humoral response. We evaluated the analytical and clinical performances of a surrogate virus neutralization test (sVNT) compared to conventional neutralization tests (cVNTs) and anti-S eCLIA assays in recovered and/or vaccinated healthcare workers. Our results indicate that sVNTs displayed high specificity and no cross-reactivity. Both eCLIA and sVNT immunoassays were good at identifying cVNT serum dilutions ≥1:16. The optimal thresholds when identifying cVNT titers ≥1:16, were 74.5 U/mL and 49.4 IU/mL for anti-S eCLIA and sVNT, respectively. Our data show that neutralizing antibody titers (Nab) differ from one individual to another and may diminish over time. Specific assays such as sVNTs could offer a reliable complementary tool to routine anti-S serological assays.

Sensitivity of three commercial tests for SARS-CoV-2 serology in children: an Italian multicentre prospective study.

BACKGROUND: US Food and Drug Administration has issued Emergency Use Authorizations for hundreds of serological assays to support Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) diagnosis. The aim of this study is to evaluate, for the first time in children, the performance of three widely utilized SARS-CoV-2 serology commercial assays, Diesse Diagnostics (IgG, IgA, IgM) and Roche Diagnostics, both Roche Nucleocapsid (N) IgG and Roche Spike (S) IgG assays. METHODS: Sensitivity and 95% confidence intervals (CIs) were estimated for each of the three different serological tests and mixed and direct comparison were performed. Univariate and multivariate Poisson regression models were fitted to calculate incidence rate ratios and 95% CIs as estimate of the effects of age, gender, time on the serology title. A p-value < 0.05 indicated statistical significance. RESULTS: Overall, 149 children were enrolled in the study. A low sensitivity was found for Diesse IgA, IgM and IgG. Compare to Diesse, Roche S had a higher sensitivity at 15-28 days from infection (0.94, 95%CI: 0.73-1.0) and Roche N at 28-84 days (0.78, 95%CI: 0.58-0.91). When a direct comparison of IgG tests sensitivity was feasible for patients with pairwise information, Roche S and Roche N showed a statistically significant higher sensitivity compared to Diesse in all the study periods, whereas there was no difference between the two Roche tests. CONCLUSION: Roche S and Roche N serology tests seem to better perform in children. Large prospective studies are needed to better define the characteristics of those tests.

Validation of Serological Methods for COVID-19 and Retrospective Screening of Health Employees and Visitors to the São Paulo University Hospital, Brazil.

Reliable serological tests for the detection of SARS-CoV-2 antibodies among infected or vaccinated individuals are important for epidemiological and clinical studies. Low-cost approaches easily adaptable to high throughput screenings, such as Enzyme-Linked Immunosorbent Assays (ELISA) or electrochemiluminescence immunoassay (ECLIA), can be readily validated using different SARS-CoV-2 antigens. A total of 1,119 serum samples collected between March and July of 2020 from health employees and visitors to the University Hospital at the University of São Paulo were screened with the Elecsys® Anti-SARS-CoV-2 immunoassay (Elecsys) (Roche Diagnostics) and three in-house ELISAs that are based on different antigens: the Nucleoprotein (N-ELISA), the Receptor Binding Domain (RBD-ELISA), and a portion of the S1 protein (ΔS1-ELISA). Virus neutralization test (CPE-VNT) was used as the gold standard to validate the serological assays. We observed high sensitivity and specificity values with the Elecsys (96.92% and 98.78%, respectively) and N-ELISA (93.94% and 94.40%, respectively), compared with RBD-ELISA (90.91% sensitivity and 88.80% specificity) and the ΔS1-ELISA (77.27% sensitivity and 76% specificity). The Elecsys® proved to be a reliable SARS-CoV-2 serological test. Similarly, the recombinant SARS-CoV-2 N protein displayed good performance in the ELISA tests. The availability of reliable diagnostic tests is critical for the precise determination of infection rates, particularly in countries with high SARS-CoV-2 infection rates, such as Brazil. Collectively, our results indicate that the development and validation of new serological tests based on recombinant proteins may provide new alternatives for the SARS-CoV-2 diagnostic market.

Antibodies against SARS-CoV-2 after natural infection in healthcare workers and clinical characteristics as putative antibody production prediction.

Introduction: There is a need for detailed data on early antibody responses against SARS-CoV-2 as this may contribute to the prediction of the clinical course of COVID-19 and the optimization of convalescent plasma treatment. This study aims to gain insight into developing antibodies to SARS-CoV-2 in health care workers (HCWs) infected in the first wave of the SARS-CoV-2 pandemic in the Netherlands. Materials and methods: In this retrospective analysis, sera from PCR-confirmed COVID-19 positive HCWs are included at the time of the initial PCR (T = 0, n = 95) and at least 21 days after the initial serum (T ≥ 21, n = 133). This study assesses correlations between qualitative total Ig, IgM, IgA, IgG, and quantitative anti-S-RBD antibody responses and participant characteristics. Results: Higher Ct values were associated with higher antibody positivity rates for total Ig (OR 1.261 (95% CI 1.095-1.452)), IgM (OR 1.373 (95% CI 1.125-1.675)), and IgA (OR 1.222 (95% CI 1.013-1.475)). Gender was predictive of IgM and IgA antibody positivity rates at T = 0 (OR 0.018 (95% CI 0.001-0.268)) and (OR 0.070 (95% CI 0.008-0.646)). At T ≥ 21, a substantial proportion of HCWs developed IgM (103/133; 77.4%) and total Ig (128/133; 96.2%) antibodies. IgA and IgG seroconversions were observed in only 51.1% (67/131) and 55.7% (73/131) of HCWs. Anti-S-RBD responses were higher when the interval between onset of symptoms and sampling was longer. Conclusion: The findings of this study give insight into early antibody responses and may have implications for the selection of convalescent plasma donors and the further development of monoclonal antibody treatment.

Head-to-Head Evaluation of Five Automated SARS-CoV-2 Serology Immunoassays in Various Prevalence Settings.

PURPOSE: To assess the diagnostic performances of five automated anti-SARS-CoV-2 immunoassays, Epitope (N), Diasorin (S1/S2), Euroimmun (S1), Roche N (N), and Roche S (S-RBD), and to provide a testing strategy based on pre-test probability. METHODS: We assessed the receiver operating characteristic (ROC) areas under the curve (AUC) values, along with the sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs), of each assay using a validation sample set of 172 COVID-19 sera and 185 negative controls against a validated S1-immunofluorescence as a reference method. The three assays displaying the highest AUCs were selected for further serodetection of 2033 sera of a large population-based cohort. RESULTS: In the validation analysis (pre-test probability: 48.1%), Roche N, Roche S and Euroimmun showed the highest discriminant accuracy (AUCs: 0.99, 0.98, and 0.98) with PPVs and NPVs above 96% and 94%, respectively. In the population-based cohort (pre-test probability: 6.2%) these three assays displayed AUCs above 0.97 and PPVs and NPVs above 90.5% and 99.4%, respectively. A sequential strategy using an anti-S assay as screening test and an anti-N as confirmatory assays resulted in a 96.7% PPV and 99.5% NPV, respectively. CONCLUSIONS: Euroimmun and both Roche assays performed equally well in high pre-test probability settings. At a lower prevalence, sequentially combining anti-S and anti-N assays resulted in the optimal trade-off between diagnostic performances and operational considerations.

Evaluation of a Broad Panel of SARS-CoV-2 Serological Tests for Diagnostic Use.

Serological testing is crucial in detection of previous infection and in monitoring convalescent and vaccine-induced immunity. During the Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) pandemic, numerous assay platforms have been developed and marketed for clinical use. Several studies recently compared clinical performance of a limited number of serological tests, but broad comparative evaluation is currently missing. Within this study, a panel of 161 sera from SARS-CoV-2 infected, seasonal CoV-infected and SARS-CoV-2 naïve subjects was enrolled to evaluate 16 ELISA/ECLIA-based and 16 LFA-based tests. Specificities of all ELISA/ECLIA-based assays were acceptable and generally in agreement with the providers' specifications, but sensitivities were lower as specified. Results of the LFAs were less accurate as compared to the ELISAs, albeit with some exceptions. We found a sporadic unequal immune response for different antigens and thus recommend the use of a nucleocapsid protein (N)- and spike protein (S)-based test combination when maximal sensitivity is necessary. Finally, the quality of the immune response in terms of neutralization should be tested using S-based IgG tests.

Spectrum Bias and Individual Strengths of SARS-CoV-2 Serological Tests-A Population-Based Evaluation.

Antibody testing for determining the SARS-CoV-2 serostatus was rapidly introduced in early 2020 and since then has been gaining special emphasis regarding correlates of protection. With limited access to representative samples with known SARS-CoV-2 infection status during the initial period of test development and validation, spectrum bias has to be considered when moving from a "test establishment setting" to population-based settings, in which antibody testing is currently implemented. To provide insights into the presence and magnitude of spectrum bias and to estimate performance measures of antibody testing in a population-based environment, we compared SARS-CoV-2 neutralization to a battery of serological tests and latent class analyses (LCA) in a subgroup (n = 856) of the larger population based TiKoCo-19 cohort (n = 4185). Regarding spectrum bias, we could proof notable differences in test sensitivities and specificities when moving to a population-based setting, with larger effects visible in earlier registered tests. While in the population-based setting the two Roche ELECSYS anti-SARS-CoV-2 tests outperformed every other test and even LCA regarding sensitivity and specificity in dichotomous testing, they didn't provide satisfying quantitative correlation with neutralization capacity. In contrast, our in-house anti SARS-CoV-2-Spike receptor binding domain (RBD) IgG-ELISA (enzyme-linked-immunosorbant assay) though inferior in dichotomous testing, provided satisfactory quantitative correlation and may thus represent a better correlate of protection. In summary, all tests, led by the two Roche tests, provided sufficient accuracy for dichotomous identification of neutralizing sera, with increasing spectrum bias visible in earlier registered tests, while the majority of tests, except the RBD-ELISA, didn't provide satisfactory quantitative correlations.

Long-Term Longitudinal Evaluation of Six Commercial Immunoassays for the Detection of IgM and IgG Antibodies against SARS CoV-2.

The number of serological assays for SARS-CoV-2 has skyrocketed in the past year. Concerns have been raised regarding their performance characteristics, depending on the disease severity and the time of the analysis post-symptom onset (PSO). Thus, independent validations using an unbiased sample selection are required for meaningful serology data interpretation. We aimed to assess the clinical performance of six commercially available assays, the seroconversion, and the dynamics of the humoral response to SARS-CoV-2 infection. The study included 528 serum samples from 156 patients with follow-up visits up to six months PSO and 161 serum samples from healthy people. The IgG/total antibodies positive percentage increased and remained above 95% after six months when chemiluminescent immunoassay (CLIA) IgG antiS1/S2 and electro-chemiluminescent assay (ECLIA) total antiNP were used. At early time points PSO, chemiluminescent microparticle immunoassay (CMIA) IgM antiS achieved the best sensitivity. IgM and IgG appear simultaneously in most circumstances, and when performed in parallel the sensitivity increases. The severe and the moderate clinical forms were significantly associated with higher seropositivity percentage and antibody levels. High specificity was found in all evaluated assays, but the sensitivity was variable depending on the time PSO, severity of disease, detection method and targeted antigen.

Antibody Responses One Year after Mild SARS-CoV-2 Infection.

Understanding the long-term kinetics of antibodies in coronavirus disease 2019 (COVID-19) is essential in interpreting serosurvey data. We investigated the antibody response one year after infection in 52 mildly symptomatic patients with severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection, using three commercial immunoassays and a surrogate virus neutralization test (sVNT) kit. Anti-N pan-immunoglobulin (Ig), anti-S IgG, and anti-S1 IgG were detected in 43 (82.7%), 44 (84.6%), and 30 (57.7%), respectively. In 49 (94.2%), the antibody could be detected by either anti-N pan-Ig or anti-S IgG assay. In the sVNT, 30 (57.7%) had positive neutralizing activity. Despite waning immunity, SARS-CoV-2 antibodies can be detected up to one year after infection, even in mild COVID-19 patients.

Detection of anti-SARS-CoV-2 antibodies in dried blood spots utilizing manual or automated spot extraction and electrochemiluminescence immunoassay (ECLIA).

Serological test methods to detect anti-SARS-CoV-2 antibodies represent a major measure to manage the pandemic caused by the coronavirus disease 2019 (COVID-19). In this communication, test results obtained from minimal-invasively collected dried blood spot (DBS) specimens, which can be sampled 'at home' without the need of medically trained personnel, are compared to conventionally collected venous blood samples. DBS samples were prepared for analysis either manually or by a card extraction robot, and electrochemiluminescence assay (ECLIA) characteristics, assay readout values as well as stability data covering a period of more than 200 days are provided. Constant anti-SARS-CoV-2 antibody readouts of quality control DBS were obtained over the entire test period using DBS specimens stored under dry and dark conditions. In addition, test results obtained from individuals tested twice within 10 months post-infection indicated a consistent presence of antibodies.

Evaluation of 18 commercial serological assays for the detection of antibodies against SARS-CoV-2 in paired serum samples.

A variety of serological tests have been developed to detect the presence of antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluated the performance of 18 commercially available SARS-CoV-2 antibody assays. Early (6-8 days after the start of symptoms) and late sera (>14 days) from ICU patients (n=10 and n=16, respectively) and healthcare workers (n=5 and n=9, respectively) were included. Additionally, 22 sera were included to detect potential cross-reactivity. Test characteristics were determined for the 18 assays. In >14 days samples, the Vircell IgG and Wantai Ig ELISAs had superior sensitivity compared to the other ELISAs (96%). Furthermore, the Roche Ig, the Epitope Diagnostics IgM, Wantai IgM, Euroimmun IgG, and IgA all showed a specificity of 100%. The POCTs of Boson Biotech and ACRO Biotech showed the highest sensitivities: 100% and 96% (83.5-99.8), respectively. The POCT of Orient Gene Biotech, VOMED Diagnostics, and Coris-Bioconcept showed highest specificities (100%). For the IgM and IgA assays, the Euroimmun IgA test showed the highest sensitivity in early samples: 46.7% (23.5-70.9) to 53.3% (29.1-76.5). In general, all tests performed better in patients with severe symptoms (ICU patients). We conclude that the Wantai Ig and Vircell IgG ELISAs may be suitable for diagnostic purposes. The IgM/IgA tests performed poorer than their IgG/Ig counterparts but may have a role in diagnoses of SARS-CoV-2 in a population in which the background seroprevalence of IgG high, and IgM and/or IgA may distinguish between acute or past infection.

Possible correlation of electrochemiluminescence based numerical cut off index value with concentration of anti-SARS-CoV-2 antibody: Is it worth reporting?

Background: Many laboratories are reporting a numerical cutoff index value (COI) value for most anti-SARS-CoV-2 qualitative tests. These numerical values in patients' report ultimately created great confusion in the public and physicians, therefore this study was designed to evaluate the correlation of electrochemiluminescence (ECLIA) based numerical COI values with quantitative ELISA of anti-SARS-CoV-2 antibody. Design and Methods: Two hundred and twenty-eight (228) recovered COVID-19 patients were included; their serum samples were analyzed by quantitative ELISA and ECLIA for anti-SARSCOV- 2 antibodies. Results: One hundred and seventy-three (75.8%) patients tested positive by ECLIA and ELISA assay and thirty-seven (6.2%) were tested negative by both methods. A weak positive correlation (r=0.37) was found between numerical COI value of ECLIA with ELISA concentration, which was statistically significant with p<0.001. All values were dispersed on scatter plot and there was no significant linear relationship between ECLIA and ELISA assay. Conclusions: As both testing techniques are base upon the same immunological phenomena of detecting antibodies against nucleocapsid protein. We suggest that COI values are not meant to describe the immunity level of the individuals thus the physicians should not consider it as a quantitative value for antibody levels in COVID-19 patients.

Clinical evaluation of the antibody response in patients with COVID-19 using automated high-throughput immunoassays.

Several automated high-throughput immunoassays for detecting anti-SARS-CoV-2 antibodies by a semi-quantitative approach have been commercialized. In this study, we describe the timeline of the antibody response in patients with RT-PCR-confirmed COVID-19. A total of 292 sequential serum samples from 33 Japanese patients were retrospectively analyzed using four test kits for SARS-CoV-2: the Abbott SARS-CoV-2 IgG assay (Abbott), Elecsys® Anti-SARS-CoV-2 assay (Roche Diagnostic), and VITROS® Anti-SARS-CoV-2 Total and IgG assays (Ortho Clinical Diagnostics). All automated immunoassays could equivalently identify positive sera collected within 2 weeks after symptom onset (99.3%-100%). In addition, the S protein-based automated immunoassay, the VITROS® Anti-SARS-CoV-2 Total assay, may play a complementary role in evaluating passive antibody therapies or vaccines against SARS-CoV-2, although further research is required.

Recent Advances in the Evaluation of Serological Assays for the Diagnosis of SARS-CoV-2 Infection and COVID-19.

Introduction: Few data on the diagnostic performance of serological tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are currently available. We evaluated sensitivity and specificity of five different widely used commercial serological assays for the detection of SARS-CoV-2-specific IgG, IgM, and IgA antibodies using reverse transcriptase-PCR assay in nasopharyngeal swab as reference standard test. Methods: A total of 337 plasma samples collected in the period April-June 2020 from SARS-CoV-2 RT-PCR positive (n = 207) and negative (n = 130) subjects were investigated by one point-of-care lateral flow immunochromatographic assay (LFIA IgG and IgM, Technogenetics) and four fully automated assays: two chemiluminescence immunoassays (CLIA-iFlash IgG and IgM, Shenzhen YHLO Biotech and CLIA-LIAISON® XL IgG, DiaSorin), one electrochemiluminescence immunoassay (ECLIA-Elecsys® total predominant IgG, Roche), and one enzyme-linked immunosorbent assay (ELISA IgA, Euroimmune). Results: The overall sensitivity of all IgG serological assays was >80% and the specificity was >97%. The sensitivity of IgG assays was lower within 2 weeks from the onset of symptoms ranging from 70.8 to 80%. The LFIA and CLIA-iFlash IgM showed an overall low sensitivity of 47.6 and 54.6%, while the specificity was 98.5 and 96.2%, respectively. The ELISA IgA yielded a sensitivity of 84.3% and specificity of 81.7%. However, the ELISA IgA result was indeterminate in 11.7% of cases. Conclusions: IgG serological assays seem to be a reliable tool for the retrospective diagnosis of SARS-CoV-2 infection. IgM assays seem to have a low sensitivity and IgA assay is limited by a substantial rate of indeterminate results.

Independent Side-by-Side Validation and Comparison of 4 Serological Platforms for SARS-CoV-2 Antibody Testing.

Highly sensitive and specific platforms for the detection of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies are becoming increasingly important for evaluating potential SARS-CoV-2 convalescent plasma donors, studying the spread of SARS-CoV-2 infections, and identifying individuals with seroconversion. This study provides a comparative validation of 4 anti-SARS-CoV-2 platforms. A unique feature of the study is the use of a representative cohort of convalescent patients with coronavirus disease 2019 and a mild to moderate disease course. All platforms showed significant correlations with a SARS-CoV-2 plaque reduction neutralization test, with highest sensitivities for the Euroimmun and the Roche platforms, suggesting their preferential use for screening persons at increased risk of SARS-CoV-2 infections.

Seroprevalence of neutralizing antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among healthcare workers in Makkah, Saudi Arabia.

OBJECTIVE: The new coronavirus disease 2019 (COVID-19) is a major health problem worldwide. The surveillance of seropositive individuals serves as an indicator to the extent of infection spread and provides an estimation of herd immunity status among population. Reports from different countries investigated this issue among healthcare workers (HCWs) who are "at risk" and "sources of risk" for COVID-19. This study aims to investigate the seroprevalence of COVID-19 among HCWs in one of the COVID-19 referral centers in Makkah, Saudi Arabia using three different serological methods. METHODS: In-house developed enzyme-linked immunoassay (ELISA), commercially available electro-chemiluminescence immunoassay (ECLIA), and microneutralization (MN) assay were utilized to determine the seroprevalence rate among the study population. 204 HCWs participated in the study. Both physicians and nurses working in the COVID-19 and non COVID-19 areas were included. Twelve out of 204 were confirmed cases of COVID-19 with variable disease severity. Samples from recovered HCWs were collected four weeks post diagnosis. RESULTS: The overall seroprevalence rate was 6.3% (13 out of 204) using the in-house ELISA and MN assay and it was 5.8% (12 out of 204) using the commercial ECLIA. Among HCWs undiagnosed with COVID-19, the seroprevalence was 2% (4 out 192). Notably, neutralizing antibodies were not detected in 3 (25%) out 12 confirmed cases of COVID-19. CONCLUSIONS: Our study, similar to the recent national multi-center study, showed a low seroprevalence of SARS-Cov-2 antibodies among HCWs. Concordance of results between the commercial electro-chemiluminescence immunoassay (ECLIA), in-house ELISA and MN assay was observed. The in-house ELISA is a promising tool for the serological diagnosis of SARS-CoV-2 infection. However, seroprevalence studies may underestimate the extent of COVID-19 infection as some cases with mild disease did not have detectable antibody responses.

SARS-CoV-2 infection serology validation of different methods: Usefulness of IgA in the early phase of infection.

BACKGROUND AND AIMS: A novel coronavirus (SARS-CoV-2) was isolated from the respiratory samples of patients with pneumonia as showed by the sequence analysis of the virus genomes obtained in Wuhan, China. The antibody response to SARS-CoV-2 is not well understood yet, but the availability of sensitive and specific serological assays will be crucial for the early diagnosis of infection, for epidemiological studies and for defining the presence of neutralizing antibodies in response to a possible vaccine. MATERIALS AND METHODS: We tested and compared the performances of one chemiluminescent immunoassay (CLIA), two enzyme-linked immunosorbent assay (ELISA) and an electrochemiluminescence immunoassay (ECLIA). RESULTS: The ECLIA serological assay performed best and may be a valid screening method for SARS-COV-2 infection. The IgA detected by the ELISA assay might be a more reliable and stable early serological marker than IgM. Instead, IgGs, as expected, showed stable level after 10 days from symptoms onset. CONCLUSION: The ECLIA method could be used as screening test, considering both the excellent performance and the cost per single test; while ELISA assay for IgG and IgA, which are present at a higher level than IgM and last longer, might be used as confirmatory test.

Antibody Responses 8 Months after Asymptomatic or Mild SARS-CoV-2 Infection.

Waning humoral immunity in coronavirus disease patients has raised concern over usefulness of serologic testing. We investigated antibody responses of 58 persons 8 months after asymptomatic or mildly symptomatic infection with severe acute respiratory syndrome coronavirus 2. For 3 of 4 immunoassays used, seropositivity rates were high (69.0%-91.4%).