Evaluation of the elecsys chagas assay for detection of trypanosoma cruzi-specific antibodies in a multicenter study in Europe and Latin America

Serology is the preferred method to confirm a Chagas disease diagnosis and to screen blood donors. A battery of assays is often required due to the limited accuracy of single assays. The Elecsys Chagas assay is a newly developed, double-antigen sandwich assay for use on the Elecsys and cobas e immunoassay analyzers, intended to identify individuals infected with Trypanosoma cruzi, for diagnosis and screening. The performance of the Elecsys Chagas assay was evaluated in comparison with those of other widely used T. cruzi antibody assays, at multiple sites (Europe/Latin America). Relative sensitivity and specificity were assessed by using samples from blood donors, pregnant women, and hospitalized patients from regions where Chagas disease is endemic and from regions of nonendemicity. The Elecsys Chagas assay had an overall relative sensitivity of 100% (n 674). Overall relative specificities were 99.90% (n 14,681), 100% (n 313), and 100% (n 517) for samples from blood donors, pregnant women, and hospitalized patients, respectively. The analytical specificity was 99.83% (n 594). The Elecsys Chagas assay detected T. cruzi antibodies in two World Health Organization (WHO) standard T. cruzi reference panels (panels 09/188 and 09/186) at a 1:512 dilution, corresponding to a cutoff sensitivity of approximately 1 mIU/ml. The Elecsys Chagas assay demonstrated robust performance under routine conditions at multiple sites in Europe and Latin America. In contrast to other available Chagas assays, the Elecsys assay uses a reduced number of recombinant T. cruzi antigens, resulting in a significantly smaller number of cross-reactions and improved analytical specificity while being highly sensitive

Overview of all results per test and VLP.

<p>Numbers indicate how many input concentrations were detected per VLP and test, i.e. 3 = 50, 10 and 2 IU/ml concentrations detected, 2 = 50 and 10 IU/ml detected, 1 = 50 IU/ml detected, 0 =  VLP not detected at any concentration. The overall sensitivity for each test was calculated as number (#) of VLPs detected (D)/total number of VLPs (n = 129, i.e. # of VLPs detected + # of VLPs not detected [ND], excluding the WHO p24 standard).</p

Amino acid sequence divergence (%) of p24 in VLP panel and LANL reference subtypes after pairwise sequence alignment.

<p>Amino acid sequence divergence (%) of p24 in VLP panel and LANL reference subtypes after pairwise sequence alignment.</p

Phylogenetic relationship between Gag amino acid sequences of VLP panel members (red) and Los Alamos National Laboratory (LANL) subtype reference sequences (black).

<p>Gag subtype reference sequences were downloaded from the LANL website <a href="http://www.hiv.lanl.gov/content/sequence/NEWALIGN/align.html" target="_blank">http://www.hiv.lanl.gov/content/sequence/NEWALIGN/align.html</a> and filtered for subtypes present in the VLP panel. The phylogenetic tree was constructed using the neighbour joining method (Clustal W). The scale bar indicates branch length, expressed as the number of substitutions per site.</p

Detection of VLPs before and after heat-denaturation at 10 IU/ml.

<p>VLP preparations of 50 IU/ml were diluted at 1:5 in PBS and heat-denatured for 5 min at 100°C. Results for the non-heat treated VLPs for the Abbot Architect and Perkin Elmer Alliance were taken from the complete panel analysis and heat-treated VLP measurement was conducted separately. For the bioMérieux VIDAS DuoUltra, heat and non-heat treated samples were analysed in parallel. Highlighted in red are VLPs with loss of p24 detection between 1.9–3-fold for the Perkin Elmer Alliance and ≥3-fold for bioMérieux VIDAS DuoUltra and Abbott Architect.</p