Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2019

Comparison of two Schistosoma IgG Enzyme immunoassays (#125)

Demi Giammichelle 1 , Jennifer Robson 1 , Kirra Callander 1
  1. Sullivan Nicolaides Pathology, Fortitude Valley, QLD, Australia

Although not endemic to Australia, Schistosomiasis serology is the mainstay for diagnosis of this chronic parasitic infection in a variety of settings including refugees, migrants and travellers to endemic countries. These groups will all have varying prevalence of infection.

The aim of this study was to compare the Euroimmun Schistosoma IgG ELISA kit to the Novalisa anti-Schistosoma IgG ELISA as feedback from clinicians had queried the specificity of the Novalisa ELISA and its potential high rate of false positive results in low risk populations.

In 2018 the seroprevalence of Schistosoma from 2480 specimens tested at Sullivan Nicoloaides Pathology was 19.2% (477) tested positive, 3.3% (81) tested equivocal, and 77.5% (1922) tested negative, with a total positive/equivocal rate of 22.5%. Positive and negative predictive values have been calculated based on a seroprevalence of 20%.

70 samples in total were tested; a sensitivity panel that included 15 high positive ( Novalisa >1.5) and 15 low positive equivocal patients (Novalisa 0.90 -1.5) samples and 40 specificity samples that included 20 challenge sample from patients with strongyloides, malaria, filariasis, and amebiasis. All specimens that had not previously been tested using the Novalisa assay (cross-reactors) were tested using both assays. For the analysis equivocal results were treated as positive.

62 episodes (88.5%) were concordant, and 8 discordant (11.5%). Based on the Novalisa results the sensitivity of the Euroimmun assay was 79.4% (CI: 62.1-91.3), specificity 97.2% (CI: 85.5-99.9); PPV 79.4% (CI: 49.2-95.3) and NPV 97.2% (87.7-99.6). Discordant analysis based on clinical history and follow up samples suggested a number of false positive calls with the Novalisa. The adjusted sensitivity of the Euroimmun assay was 96.4% (CI: 79.8-99.8), specificity 97.6% (CI: 85.5-99.9); PPV 92.9% (CI: 64.2-99.6) and NPV 99.1% (89.2-99.9). Cross reactions with Strongyloides positive specimens and a malaria specimen for both assays. The Euroimmun assay was less likely to detect false positive results in the HIV insurance specificity panel.