Performance Evaluation: Four Chemiluminescent SARS-Cov-2 Immunoassays and Rapid-Card Test in Mild Disease and Seroprevalence of SARS CoV-2 in Frontline Healthcare Workers

Introduction: The COVID-19 pandemic raised a host of challenges to modern medicine. Key amongst these were in diagnostics, as most SARS-CoV-2 assays had been rapidly developed and released under emergency-use authorization with limited validation on clinical samples and secondly, an increased risk of COVID-19 infection to healthcare workers (HCW). There are limited inter-assay comparisons to detect SARS-CoV-2 antibodies in cases with milder symptoms of COVID-19, necessary to evaluate whether assays can detect SARS-CoV-2 antibodies in patients with mild infection.

Aim: Therefore this study aimed to evaluate the performance of four chemiluminescence immunoassays and a rapid immunochromatographic assay in 100 rRT-PCR diagnosed-recovered frontline HCW with milder COVID-19 disease and secondly to evaluate the seroprevalence of SARS-CoV-2 infection in the asymptomatic frontline HCW at a multispeciality hospital in Delhi, India.
Study Design: Serum and plasma samples were obtained from 100 rRT-PCR diagnosed-recovered frontline HCWs with mild disease working across the hospital, and performance of four common chemiluminescence immunoassays evaluated. Also samples of 505 asymptomatic, frontline HCWs working in hospital, who had not developed or shown any symptoms of COVID-19 infection to date was collected and the seroprevalence of infection was evaluated.

Place and Duration of the Study: A study was conducted at BLK Superspeciality Hospital, New Delhi from September to October 2020.

Methods: Four chemiluminescence immunoassays [Abbott SARS-CoV-2 IgG (Nucleocapsid), Roche Elecsys® Anti-SARS-CoV-2 Total (Nucleocapsid), Ortho-Clinical Diagnostics: VITROS Anti-SARS-CoV-2 IgG (Spike) and Anti-SARS-CoV-2 Total (Spike)] and a rapid assay [Medsource Ozone Biomedicals] were evaluated in 100 rRT-PCR diagnosed-recovered frontline HCW with mild disease. Also, seroprevalence was studied in 505 asymptomatic, frontline HCW.

Results: At manufacturers' thresholds, overall sensitivity for Abbott was 71%, Roche 96%, Ortho (both total and IgG(S) 99% and rapid card 56%. Seroprevalence in asymptomatic frontline HCW was found to be 17.6%, with positivity being higher in the HCW group not facing patients directly compared to direct patient caregivers (P = 0.0034).

Conclusion: Assay performance depends on assay design (total IgM & IgG antibodies versus IgG alone), choice of antigen, and time of sample testing from the onset of disease. In our study, Ortho Vitros total-Ab; IgG (Spike), and Roche Elecsys total-Ab (Nucleocapsid) assays were found to have optimal sensitivity. A seroprevalence study in the frontline HCWs at our institute showed that seroprevalence was higher (17.6%) in HCWs in comparison to the community.