Validation of a diphtheria toxoid multiplex bead assay for serosurveys

Area of Science:

• Immunology
• Vaccinology
• Diagnostic Assay Development

Background:

• Diphtheria remains a global health concern, necessitating reliable methods to assess population immunity.
• Accurate measurement of diphtheria toxoid IgG antibodies is crucial for evaluating vaccine effectiveness and guiding public health strategies.
• The gold standard Vero cell toxin neutralization test (VNT) is complex and not suitable for high-throughput screening.

Purpose of the Study:

• To validate a novel multiplex bead assay for quantifying diphtheria toxoid-specific IgG antibodies.
• To compare the performance of the multiplex assay against the established VNT.
• To assess the diagnostic accuracy of the multiplex assay for determining seroprotection against diphtheria.

Main Methods:

• A multiplex bead immunoassay was developed and validated using 1300 human serum specimens.
• Results from the multiplex assay were correlated with those obtained from the VNT.
• Sensitivity, specificity, and agreement were calculated at predefined seroprotection cutoffs.

Main Results:

• The multiplex bead assay demonstrated strong correlation (r=0.88) with the VNT.
• At the minimal seroprotection cutoff (≥0.01 IU/mL), the assay showed 95% sensitivity and 83% specificity.
• Agreement across three antibody level categories (<0.01, 0.01–<0.1, ≥0.1 IU/mL) was 81% (kappa=0.71).

Conclusions:

• The validated multiplex bead assay is a reliable and efficient tool for measuring diphtheria toxoid IgG antibodies.
• This assay provides a high-throughput alternative to the VNT for assessing population immunity and vaccine response.
• The assay's performance supports its use in epidemiological studies and public health surveillance for diphtheria.