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. 2022 Oct 12;75(8):1351-1358.
doi: 10.1093/cid/ciac160.

Measurement of Severe Acute Respiratory Syndrome Coronavirus 2 Antigens in Plasma of Pediatric Patients With Acute Coronavirus Disease 2019 or Multisystem Inflammatory Syndrome in Children Using an Ultrasensitive and Quantitative Immunoassay

George B Sigal  1 , Tanya Novak  2 , Anu Mathew  1 , Janet Chou  3 , Yubo Zhang  4 , Navaratnam Manjula  1 , Pradeepthi Bathala  1 , Jessica Joe  1 , Nikhil Padmanabhan  1 , Daniel Romero  1 , Gabriella Allegri-Machado  5 , Jill Joerger  5 , Laura L Loftis  6 , Stephanie P Schwartz  7 , Tracie C Walker  7 , Julie C Fitzgerald  8 , Keiko M Tarquinio  9 , Matt S Zinter  10 , Jennifer E Schuster  11 , Natasha B Halasa  12 , Melissa L Cullimore  13 , Aline B Maddux  14 , Mary A Staat  15 , Katherine Irby  16 , Heidi R Flori  17 , Bria M Coates  18 , Hillary Crandall  19 , Shira J Gertz  20 , Adrienne G Randolph  2 , Nira R Pollock  21 ; Overcoming COVID-19 Investigators
Affiliations

Measurement of Severe Acute Respiratory Syndrome Coronavirus 2 Antigens in Plasma of Pediatric Patients With Acute Coronavirus Disease 2019 or Multisystem Inflammatory Syndrome in Children Using an Ultrasensitive and Quantitative Immunoassay

George B Sigal et al. Clin Infect Dis. .

Abstract

Background: Detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in blood has high sensitivity in adults with acute coronavirus disease 2019 (COVID-19), but sensitivity in pediatric patients is unclear. Recent data suggest that persistent SARS-CoV-2 spike antigenemia may contribute to multisystem inflammatory syndrome in children (MIS-C). We quantified SARS-CoV-2 nucleocapsid (N) and spike (S) antigens in blood of pediatric patients with either acute COVID-19 or MIS-C using ultrasensitive immunoassays (Meso Scale Discovery).

Methods: Plasma was collected from inpatients (<21 years) enrolled across 15 hospitals in 15 US states. Acute COVID-19 patients (n = 36) had a range of disease severity and positive nasopharyngeal SARS-CoV-2 RT-PCR within 24 hours of blood collection. Patients with MIS-C (n = 53) met CDC criteria and tested positive for SARS-CoV-2 (RT-PCR or serology). Controls were patients pre-COVID-19 (n = 67) or within 24 hours of negative RT-PCR (n = 43).

Results: Specificities of N and S assays were 95-97% and 100%, respectively. In acute COVID-19 patients, N/S plasma assays had 89%/64% sensitivity; sensitivities in patients with concurrent nasopharyngeal swab cycle threshold (Ct) ≤35 were 93%/63%. Antigen concentrations ranged from 1.28-3844 pg/mL (N) and 1.65-1071 pg/mL (S) and correlated with disease severity. In MIS-C, antigens were detected in 3/53 (5.7%) samples (3 N-positive: 1.7, 1.9, 121.1 pg/mL; 1 S-positive: 2.3 pg/mL); the patient with highest N had positive nasopharyngeal RT-PCR (Ct 22.3) concurrent with blood draw.

Conclusions: Ultrasensitive blood SARS-CoV-2 antigen measurement has high diagnostic yield in children with acute COVID-19. Antigens were undetectable in most MIS-C patients, suggesting that persistent antigenemia is not a common contributor to MIS-C pathogenesis.

Keywords: COVID-19; SARS-CoV-2; antigen; antigenemia; ultrasensitive immunoassay.

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Conflict of interest statement

Potential conflicts of Interest . G. B. S., A. M., N. M., P. B, J. J., N. P., and D. R. are employees of Meso Scale Diagnostics. N. B. H. receives unrelated research support from Sanofi and Quidel. J. E. S. has received unrelated research support from Merck. H. R. F. is an Advisor for LuciraHealth. A. G. R. reports grants or contracts from National Institute of Allergy and Infectious Diseases to the institution outside of the submitted work; royalties or licenses from UpToDate for Pediatric Critical Care Section Editor; and is an unpaid Treasurer for International Sepsis Forum. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Figures

Figure 1.
Figure 1.
Measured levels of SARS-CoV-2 nucleocapsid (N) and spike (S) antigen in the plasma of children and young-adult study participants. Participants were classified as controls with samples collected prior to 2020 (Pre-COVID-19; n = 67), controls ruled out for acute COVID-19 by negative nasopharyngeal swab RT-PCR (COVID-19 Negative; n = 43), patients with RT-PCR–confirmed acute COVID-19 infections (COVID-19 Acute; n = 36), and patients diagnosed as MIS-C (COVID-19 MIS-C; n = 53). Data points are colored based on the results of the most recent clinical COVID-19 RT-PCR test prior to sample collection. Of the patients with MIS-C, the most recent clinical RT-PCR results prior to research blood sample collection were as follows: 20 RT-PCR positive, 29 RT-PCR negative, 4 NA (3 not performed, 1 inconclusive). The horizontal dashed red lines represent the assay thresholds for classifying samples as antigen positive. Abbreviations: COVID-19, coronavirus disease 2019; MIS-C, multisystem inflammatory syndrome in children; NA, not available; Neg, negative; Pos, positive; RT-PCR, reverse transcription–polymerase chain reaction; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.
Figure 2.
Figure 2.
Measured levels of plasma IgG antibodies against SARS-CoV-2 nucleocapsid (N) and spike (S) antigens and correlation with concentrations of N and S antigens. (A) Measurement of IgG antibodies against SARS-CoV-2 N and S antigen in the plasma of children and young-adult study participants. Participants were classified as described in Figure 1. Data points are colored based on the results of the most recent clinical COVID-19 RT-PCR test prior to sample collection. The horizontal dashed red lines represent the assay thresholds for classifying samples as antibody positive (Supplementary Methods). (B, C) Correlation of the levels of antigen and anti-antigen antibodies for SARS-CoV-2 N (B) and S (C) for the data points categorized as COVID-19 Acute or COVID-19 MIS-C in Figures 1 and 2a. Horizontal and vertical dashed yellow lines represent the assay thresholds for classifying samples as antigen or antibody positive, respectively. Abbreviations: COVID-19, coronavirus disease 2019; IgG, immunoglobulin G; MIS-C, multisystem inflammatory syndrome in children; NA, not available; Neg, negative; Pos, positive; RT-PCR, reverse transcription–polymerase chain reaction; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.
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References

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