SARS-CoV-2 antibody-based SURVEILLANCE: New light in the SHADOW

Serological diagnostic for SARS-CoV-2: an experimental External Quality Assessment Scheme

OBJECTIVES

Numerous analytical systems, rapidly made available on the market throughout the SARS-CoV-2 pandemic, aim to detect COVID-19, and to continuously update and improve the same systems. Medical laboratory professionals have also developed in-house analytical procedures in order to satisfy the enormous volume of requests for tests. These developments have highlighted the need control the analytical procedures used in order to guarantee patient safety. The External Quality Assessment (EQA) Scheme, an important quality assurance tool, aims to guarantee high standard performance for laboratory and analytical procedures. The aim of the present study was to report on the results collected in an experimental EQA scheme for the serological diagnosis of SARS-CoV-2.

METHODS

All qualitative results collected in the different EQA surveys were summarized in order to identify the percentage of laboratory results in relation to typology of antibodies, results and samples.

RESULTS

A total of 4,867 data sets were collected. The analysis of EQA data made, demonstrates a better agreement among laboratories results for total Ig than single immunoglobulins (IgG, IgM, IgA) in the case samples positive for SARS-CoV-2, and a wide divergence between IgM results for positive samples (only 34.9% were correct). Results for negative controls and specificity controls demonstrated a better overall agreement than results for positive samples.

CONCLUSIONS

Working in collaboration with the IVD manufacturers, laboratory professionals must strive to achieve harmonization of results, and to develop well-defined protocols complying with the ISO 15189 requirements.

Laboratory medicine in the COVID-19 era: six lessons for the future

The lockdown due to the coronavirus disease 2019 (COVID-19), a major healthcare challenge, is a worldwide threat to public health, social stability, and economic development. The pandemic has affected all aspects of society, dramatically changing our day-to-day lives and habits. It has also changed clinical practice, including practices of clinical laboratories. After one year, it is time to rethink what has happened, and is still happening, in order to learn lessons for the future of laboratory medicine and its professionals. While examining this issue, I was inspired by Italo Calvino's famous work, "Six memos for the next millennium".But I rearranged the Author's six memos into "Visibility, quickness, exactitude, multiplicity, lightness, consistency".

Antibody response to first and second dose of BNT162b2 in a cohort of characterized healthcare workers

BACKGROUND

Vaccine-induced population immunity is a key global strategy to control coronavirus disease 2019 (COVID-19). The rapid implementation and availability of several COVID-19 vaccines is now a global health-care priority but more information about humoral responses to single- and double-dose vaccine is needed.

METHODS

163 health care workers (HCW) of the Padua University Hospitals, who underwent a complete vaccination campaign with BNT162b2 vaccine were asked to collect serum samples at 12 (t12) and 28 (t28) days after the first inoculum to allow the measurement of SARS-CoV-2 Antibodies (Ab) using chemiluminescent assays against the spike (S) protein and the Receptor Binding Domain (RBD) of the virus, respectively.

RESULTS

Significant differences were found at t12 for infection-naïve and subjects with previous-natural infection who present higher values of specific antibodies, while no significant differences have been found between t12 and t28. No statistically significant difference was found between male and female, while lower Ab levels have been observed in subjects older than 60 years at t12 but not at t28.

CONCLUSIONS

Our study confirms observed differences in vaccine responses between infection-naïve and subjects with previous natural infection at t12 but not for a longer time. The influence of sex and age deserves further studies, even if the relationship with age seems particularly significant.

Analytical and clinical performances of a SARS-CoV-2 S-RBD IgG assay: comparison with neutralization titers

OBJECTIVES

SARS-CoV-2 serology presents an important role in several aspects of COVID-19 pandemic. Immunoassays performances have to be accurately evaluated and correlated with neutralizing antibodies. We investigated the analytical and clinical performances of a SARS-CoV-2 RBD IgG assay, automated on a high throughput platform, and the correlation of the antibodies (Ab) levels with the plaque reduction neutralization (PRNT₅₀) Ab titers.

METHODS

A series of 546 samples were evaluated by SARS-CoV-2 RBD IgG assay (Snibe diagnostics), including 171 negative and 168 positive SARS-CoV-2 subjects and a further group of 207 subjects of the COVID-19 family clusters follow-up cohort.

RESULTS

Assay imprecision ranged from 3.98 to 12.18% being satisfactory at low and medium levels; linearity was excellent in all the measurement range. Considering specimens collected after 14 days post symptoms onset, overall sensitivity and specificity were 99.0 and 92.5%, respectively. A total of 281 leftover samples results of the PRNT₅₀ test were available. An elevated correlation was obtained between the SARS-CoV-2 RBD IgG assay and the PRNT₅₀ titer at univariate (ρ=0.689) and multivariate (ρ=0.712) analyses.

CONCLUSIONS

SARS-CoV-2 S-RBD IgG assay shows satisfactory analytical and clinical performances, and a strong correlation with sera neutralizing activity.

Salivary SARS-CoV-2 antigen rapid detection: A prospective cohort study

Background and aim

SARS-CoV-2 quick testing is relevant for the containment of new pandemic waves. Antigen testing in self-collected saliva might be useful. We compared salivary and naso-pharyngeal swab (NPS) SARS-CoV-2 antigen detection by a rapid chemiluminescent assay (CLEIA) and two different point-of-care (POC) immunochromatographic assays, with results of molecular testing.

Methods

234 patients were prospectively enrolled. Paired self-collected saliva (Salivette) and NPS were obtained to perform rRT-PCR, chemiluminescent (Lumipulse G) and POC (NPS: Fujirebio and Abbott; saliva: Fujirebio) for SARS-CoV-2 antigen detection.

Results

The overall agreement between NPS and saliva rRT-PCR was 78.7%, reaching 91.7% at the first week from symptoms. SARS-CoV-2 CLEIA antigen was highly accurate in distinguishing positive and negative NPS (ROC-AUC = 0.939, 95%CI:0.903–0.977), with 81.6% sensitivity and 93.8% specificity. This assay on saliva reached the optimal value within 7 days from symptoms onset (Sensitivity: 72%; Specificity: 97%). Saliva POC antigen was limited in sensitivity (13%), performing better in NPS (Sensitivity: 48% and 66%; Specificity: 100% and 99% for Espline and Abbott respectively), depending on viral loads.

Conclusions

Self-collected saliva is a valid alternative to NPS for SARS-CoV-2 detection by molecular, but also by CLEIA antigen testing, which is therefore potentially useful for large scale screening.