910. Evaluation of an Enzymatic Immunoassay System for Detection and Differentiation of Rat Hepatitis E Virus Infection in Humans

BACKGROUND: Previously, hepatitis E in humans was believed to be caused exclusively by species A variants of the Orthohepevirus genus (HEV-A) of the family Hepeviridae. However, we have previously demonstrated that Orthohepevirus species C (HEV-C), also known as rat hepatitis E virus, also causes hepatitis in humans. Due to high sequence divergence between HEV-A and HEV-C, serological tests based on HEV-A are often insensitive for HEV-C diagnosis. Therefore, we developed an enzymatic immunoassay (EIA) system for differentiating HEV-A and HEV-C antibody signatures in patient sera. METHODS: HEV-A and HEV-C peptide homologs spanning the entire immunogenic E2s region of HEV ORF2 capsid protein were expressed in E. coli. These peptides, HEV-A4 p239 and HEV-C p241, form virus-like particles (figure 1). Both peptides were coated in separate 96-well plates. Sera obtained from patients with RT-PCR confirmed acute HEV-A infection (n = 54), HEV-C infection (n = 15), and uninfected HEV seronegative controls (n = 126) were tested in parallel in HEV-A4 p239 and HEV-C p241 EIAs for respective IgG antibodies. Sample optical densities (ODs) were divided by mean OD + 3SD of the seronegative controls to generate signal/noise (S/N) ratios. S/Ns marking positivity in either assay were determined by ROC analysis. An algorithm for assay interpretation was developed (table 1) and the performance of this algorithm was measured against the RT-PCR gold standard. HEV-A4 p239 and HEV-C1 p241 virus like particles [Image: see text] Transmission electron microscopy images of the two peptides used in this study Diagnostic testing algorithm interpretation [Image: see text] Interpretation of results of testing using parallel enzymatic immunoassays RESULTS: Using cutoffs determined by ROC analysis (figure 2), HEV-A4 p239 and HEV-C p241 EIAs detected species-specific antibody responses well (sensitivity: 92.6% and 80% respectively) and were specific (92.9% and 98.3% respectively). The DC was 100% congruent with HEV-C RT-PCR and 88.9% congruent with HEV-A RT-PCR in RT-PCR positive samples. Incorporating all three cutoffs into the algorithm, we derived a 3×3 confusion matrix of RT-PCR sample assignation vs EIA algorithm classification (table 2). The Cohen’s κ value was 0.883 indicating excellent inter-rater reliability. ROC analysis for determining S/N cutoffs [Image: see text] Curve for A/A represents analysis for HEV-A4 p239 EIA. Curve for C/¬C represents analysis for HEV-C p241 EIA. Curve for r(C/A) represents analysis for the differentiating ratio. 3×3 confusion matrix comparing sample assignations by RT-PCR vs. EIA algorithm [Image: see text] CONCLUSION: A parallel EIA system accurately differentiated HEV-A and HEV-C serological signatures in acute patient sera. This method can now be applied to seroprevalence studies to determine seroprevalence of rat hepatitis E in human populations. DISCLOSURES: Siddharth Sridhar, FRCPath, Abbott (Other Financial or Material Support, Speaker’s honoraria)