Analytic comparison between three high-throughput commercial SARS-CoV-2 antibody assays reveals minor discrepancies in a high-incidence population

Abstract

Performance of three automated commercial serological IgG-based assays was investigated for assessing SARS-CoV-2 "ever" (past or current) infection in a population-based sample in a high exposure setting. PCR and serological testing was performed on 394 individuals. SARS-CoV-2-IgG seroprevalence was 42.9% (95% CI 38.1-47.8%), 40.6% (95% CI 35.9-45.5%), and 42.4% (95% CI 37.6-47.3%) using the CL-900i, VidasIII, and Elecsys assays, respectively. Between the three assays, overall, positive, and negative percent agreements ranged between 93.2-95.7%, 89.3-92.8%, and 93.8-97.8%, respectively; Cohen's kappa statistic ranged from 0.86 to 0.91; and 35 specimens (8.9%) showed discordant results. Among all individuals, 12.5% (95% CI 9.6-16.1%) had current infection, as assessed by PCR. Of these, only 34.7% (95% CI 22.9-48.7%) were seropositive by at least one assay. A total of 216 individuals (54.8%; 95% CI 49.9-59.7%) had evidence of ever infection using antibody testing and/or PCR during or prior to this study. Of these, only 78.2%, 74.1%, and 77.3% were seropositive in the CL-900i, VidasIII, and Elecsys assays, respectively. All three assays had comparable performance and excellent agreement, but missed at least 20% of individuals with past or current infection. Commercial antibody assays can substantially underestimate ever infection, more so when infection rates are high.

Figure 1

Distribution of polymerase chain reaction (PCR) cycle threshold (Ct) values of (A) the 49 persons identified as SARS-CoV-2 PCR-positive at the time of specimen collection during the study, (B) the 17 persons identified as SARS-CoV-2 PCR-positive, but were antibody-positive in at least one of the assays, and (C) the 32 persons identified as SARS-CoV-2 PCR-positive, but were antibody-negative in all three assays.

Figure 2

Distribution of the optical density values in those seronegative versus those seropositive for each assay. Red line indicates the manufacturer’s cut-off values. Blue line indicates the empirically determined optical density cut-off values as informed by the literature^,.