Technical evaluation of the InBios Strongy Detect IgG ELISA assay for the diagnosis of Strongyloides stercoralis infection

Abstract

Background Strongyloidiasis is a neglected tropical disease (NTD) caused by the soil-transmitted helminth Strongyloides stercoralis, recently included in the 2030 targets of the World Health Organization for the control of STHs. Assessment of infection prevalence is fundamental for decision-making about the implementation of control programs, but diagnostic assays to be applied in such context require evaluation. Seroassays based on recombinant antigens, which could be produced in a standardized and scalable manner, are particularly appealing for use in control programs. In this study, we performed a technical evaluation of the InBios Strongy Detect IgG ELISA, based on recombinant antigens NIE and SsIR, which has shown promising for field use. Methods A total of 46 plasma samples from Ethiopian children were used for this technical evaluation. Repeatability was evaluated on duplicate samples per plate, on four plates per day for 3 days using Bland–Altman plots, analysis of residuals, and variance components analysis. Three samples were selected for evaluation of the uniformity of test results within a single plate (border effect) by two-sided t-test. Correlation between samples and internal ELISA positive controls was analyzed using Spearman’s rank correlation coefficient applied on the results of 777 samples analyzed with the assay in a previous field-based study. Results Within and between plate residuals ranged from −0.05 to + 0.05 and −0.1 to + 0.1, respectively. Total variance was estimated at 0.327; 99.6% of variation could be attributed to the samples. There was no systematic border effect and a negligible correlation between positive internal control and samples results (R2 = 0.213; p < 0.001). Conclusion The results obtained in this study, in highly controlled conditions, point toward the InBios Strongy Detect IgG ELISA assay being reproducible, with no systematic border effect. These results encourage further assay’s development and evaluation for use in practice, including determination of preset cutoff values for positivity, which is currently not provided. Graphical Abstract