Evaluation of Ortho VITROS and Roche Elecsys S and NC Immunoassays for SARS-CoV-2 Serosurveillance Applications

Abstract

SARS-CoV-2 seroprevalence studies are instrumental in monitoring epidemic activity and require well-characterized, high-throughput assays, and appropriate testing algorithms. The U.S. Nationwide Blood Donor Seroprevalence Study performed monthly cross-sectional serological testing from July 2020 to December 2021, implementing evolving testing algorithms in response to changes in pandemic activity. With high vaccine uptake, anti-Spike (S) reactivity rates reached >80% by May 2021, and the study pivoted from reflex Roche anti-nucleocapsid (NC) testing of Ortho S-reactive specimens to parallel Ortho S/NC testing. We evaluated the performance of the Ortho NC assay as a replacement for the Roche NC assay and compared performance of parallel S/NC testing on both platforms. Qualitative and quantitative agreement of Ortho NC with Roche NC assays was evaluated on preselected S/NC concordant and discordant specimens. All 190 Ortho S+/Roche NC+ specimens were reactive on the Ortho NC assay; 34% of 367 Ortho S+/Roche NC- specimens collected prior to vaccine availability and 43% of 37 Ortho S-/Roche NC+ specimens were reactive on the Ortho NC assay. Performance of parallel S/NC testing using Ortho and Roche platforms was evaluated on 200 specimens collected in 2019 and 3,903 study specimens collected in 2021. All 200 pre-COVID-19 specimens tested negative on the four assays. Cross-platform agreement between Roche and Ortho platforms was 96.4% (3,769/3,903); most discordant results had reactivity close to the cutoffs on the alternate assays. These findings, and higher efficiency and throughput, support the use of parallel S/NC testing on either Roche or Ortho platforms for large serosurveillance studies. IMPORTANCE Seroprevalence studies like the U.S. Nationwide Blood Donor Seroprevalence Study (NBDS) have been critical in monitoring SARS-CoV-2 epidemic activity. These studies rely on serological assays to detect antibodies indicating prior infection. It is critical that the assays and testing algorithms used in seroprevalence studies have adequate performance (high sensitivity, high specificity, ability to discriminate vaccine-induced and infection-induced antibodies, etc.), as well as appropriate characteristics to support large-scale studies, such as high throughput and low cost. In this study we evaluated the performance of Ortho's anti-nucleocapsid assay as a replacement for the Roche anti-nucleocapsid assay and compared performance of parallel anti-spike and anti-nucleocapsid testing on both platforms. These data demonstrate similar performance of the Ortho and Roche anti-nucleocapsid assays and that parallel anti-spike and anti-nucleocapsid testing on either platform could be used for serosurveillance applications.

Keywords: COVID-19; SARS-CoV-2; antibodies; serology; serosurveillance; serosurvey.

FIG 1

Comparison of Ortho and Roche nucleocapsid (NC) assays numeric outputs (S/CO and COI). Ortho NC and Roche NC numeric outputs on preselected specimens tested to validate the Ortho NC assay to replace the Roche NC assay. A) Ortho S+/Roche NC+ shown in orange and Ortho S-/Roche NC- shown in black (n = 190 and n = 200;, respectively). B) Ortho S-/Roche NC+ (n = 37). C) Ortho S+/Roche NC- (n = 367). In (B) and (C), red and blue symbols denote Ortho NC nonreactive and reactive specimens, respectively. Gray lines on the axes denote manufacturer-set cutoffs.

FIG 2

Numeric outputs from Ortho and Roche parallel testing for the antigen concordant nonreactive and reactive groups (S-/NC- and S+/NC+; n = 2365). (A) Numeric outputs of the two S assays. Gray line at 0.8 and 1 denote manufacturer set cutoff for the Roche and Ortho S assays, respectively. (B) Numeric outputs of the two NC assays. Gray lines at 1 on both axes denote manufacturer set cutoff for the Roche and Ortho NC assays.

FIG 3

Numeric output of specimens tested S+/NC+ on either or both platforms for detection of seroreactivity resulting from prior SARS-CoV-2 infection (n = 1057). (A) Numeric outputs of the two S assays. Gray lines at 0.8 and 1 denote manufacturers’ cutoffs for the Roche and Ortho S assays, respectively. (B) Numeric outputs of the two NC assays. Gray lines at 1 on both axes denote manufacturers’ cutoffs for the respective assays. Blue marks denote S+/NC+ reactive samples on both platforms, yellow marks S+/NC+ on Ortho only, and red marks S+/NC+ on Roche only.

FIG 4

Roche and Ortho NC assay numeric outputs for specimens classified as S- on both platforms and NC+ on either or both platforms representing differential detection of NC-only reactive samples (n = 17). Blue, yellow, and red symbols denote specimens in agreement between the two platforms, NC- on the Roche platform, and NC- on the Ortho platform, respectively.

FIG 5

Testing results of longitudinal CCP donor specimens on Ortho and Roche assays/platforms (n = 133). (A) Ortho assays/platform results, (B) Roche assays/platform results. Black lines represent weighted geometric means for 0–60 and 100+ time periods for each assay. 95% confidence intervals, calculated using a bootstrapping method, are shown in red for each assay’s weighted geometric mean at each time period.