In total, 127 patients exposed to SARS-CoV-2 were included in the study. Among them 68 (53.54%) were patients hospitalized the Department of Infectious Diseases and Neuroinfections at the Medical University of Bialystok and 59 (46.46%) were healthcare workers exposed to the virus, but without symptoms of infection. Blood samples for immunoserological diagnostic were collected from all the patients in the study one month after the exposition.
The study was approved by the Bioethical Commission of Medical University of Bialystok APK.002.259.2020. All patients signed informed consent for participation in the study.
Two serological tests have been used:
The SARS-CoV-2 IgG assay chemiluminescent microparticle immunoassay (CMIA) used for qualitative detection of IgG antibodies to SARS-CoV-2 in human plasma or serum on the Alinity system (ABBOTT) anti-N protein
The LIAISON® SARS-CoV-2 S1/S2 IgG chemiluminescence immunoassay (CLIA) technology for the quantitative determination of anti-S1 and anti-S2 specific IgG antibodies to SARS-CoV-2 (DiaSorin)
1. SARS-CoV-2 IgG - ALINITY (ABBOTT)
The SARS-CoV-2 IgG assay is a chemiluminescent microparticle immunoassay (CMIA) used for qualitative detection of IgG antibodies to SARS-CoV-2 in human plasma or serum on the Alinity system (ABBOTT). This assay is an automated two-step immunoassay. Sample SARS-CoV-2 antigen coated paramagnetic microparticles. The IgG antibodies to SARS- CoV-2 present in the sample bind to the SARS-CoV-2 antigen coated microparticles. Anti-human IgG acridinium-labeled conjugate is added to create a reaction mixture and incubated. The resulting chemiluminescent reaction is measured as a relative light unit (RLU). There is direct relationship between the amount of IgG antibodies to SARS-CoV-2 in the sample and the RLU detected by the system optics. This relationship is reflected in the calculated index (S/C). The titer above > 1,4 was considered as positive .
2. LIAISON® SARS-CoV-2 S1/S2 IgG
The specific recombinant S1 and S2 antigens are used for coating magnetic particles (solid phase) and mouse monoclonal antibodies to human IgG are linked to an isoluminol derivative (isoluminol-antibody conjugate). During the first incubation, the SARS-CoV-2 IgG antibodies present in calibrators, samples or controls bind to the solid phase through the recombinant S1 and S2 antigens. During the second incubation the antibody conjugate reacts with IgG to SARS-CoV-2 already bound to the solid phase. After each incubation, the unbound material is removed with a wash cycle. Subsequently, the starter reagents are added and a flash chemiluminescence reaction is thus induced. The light signal, and hence the amount of isoluminol-antibody conjugate, is measured by a photomultiplier as relative light units (RLU) and is indicative of IgG to SARS-CoV2 concentration present in calibrators, samples or controls. The titer above 15 AU/Ml was considered as positive .
All methods were carried out in accordance with relevant guidelines and regulations.
Statistical analysis was performed by using STATISTICA Data Miner + QC. For immeasurable features percentage was counted. P value <0.05 was considered statistically significant.