Performance Characteristics of the Abbott Architect SARS-CoV-2 IgG Assay and Seroprevalence in Boise, Idaho

Abstract

Coronavirus disease 2019 (COVID-19), the novel respiratory illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is associated with severe morbidity and mortality. The rollout of diagnostic testing in the United States was slow, leading to numerous cases that were not tested for SARS-CoV-2 in February and March 2020 and necessitating the use of serological testing to determine past infections. Here, we evaluated the Abbott SARS-CoV-2 IgG test for detection of anti-SARS-CoV-2 IgG antibodies by testing 3 distinct patient populations. We tested 1,020 serum specimens collected prior to SARS-CoV-2 circulation in the United States and found one false positive, indicating a specificity of 99.90%. We tested 125 patients who tested reverse transcription-PCR (RT-PCR) positive for SARS-CoV-2 for whom 689 excess serum specimens were available and found that sensitivity reached 100% at day 17 after symptom onset and day 13 after PCR positivity. Alternative index value thresholds for positivity resulted in 100% sensitivity and 100% specificity in this cohort. We tested specimens from 4,856 individuals from Boise, ID, collected over 1 week in April 2020 as part of the Crush the Curve initiative and detected 87 positives for a positivity rate of 1.79%. These data demonstrate excellent analytical performance of the Abbott SARS-CoV-2 IgG test as well as the limited circulation of the virus in the western United States. We expect that the availability of high-quality serological testing will be a key tool in the fight against SARS-CoV-2.

Keywords: Abbott; COVID; COVID-19; Idaho; SARS; SARS-CoV-2; coronavirus; serology.

FIG 1

Performance characteristics of the Abbott SARS-CoV-2 IgG test. (A) Specificity was determined using 1,020 serum specimens taken before circulation of SARS-CoV-2 in the United States. Index values by sample are shown in rank order, and samples with index values greater than 0.7 are labeled. (B) Sensitivity by day since symptom onset and PCR positivity is depicted for 689 excess serum specimens comprising 415 unique patient follow-up days from 125 unique patients, using the manufacturer’s recommended positivity index value cutoff of 1.40. (C and D) Index values are depicted by day since symptom onset (C) or PCR positivity (D). Index values were averaged for patients with multiple specimens from the same day. The index value threshold of 1.40 for positivity is depicted by the red horizontal dashed line.

FIG 2

Receiver operating characteristic curves for the Abbott SARS-CoV-2 IgG test based on ≥17 days (A), ≥14 days (B), ≥10 days (C), and ≥7 days (D) after symptom onset or PCR positivity. Minimum specificity was set to 99.5%.

FIG 3

Variation among biological replicates is explained by seroconversion. (A) Coefficient of variation versus index value is depicted for biological serum replicates from individuals who had more than 3 serum or plasma samples drawn on the same calendar day. Data points representing specimens taken from individuals who were seroconverting during the repeat sampling period are in red. (B) Index value over time since symptom onset is shown for seven individuals who seroconverted and one who failed to meet the positivity threshold during the sampling period. Each individual is represented by a different color. The index value threshold of 1.40 for positivity is depicted by the red horizontal dashed line.