Quantitative Thresholds Enable Accurate Identification of Clostridium difficile Infection by the Luminex xTAG Gastrointestinal Pathogen Panel

Abstract

colonizes the gastrointestinal (GI) tract, resulting in either asymptomatic carriage or a spectrum of diarrheal illness. If clinical suspicion for is low, stool samples are often submitted for analysis by multiplex molecular assays capable of detecting multiple GI pathogens, and some institutions do not report this organism due to concerns for high false-positive rates. Since clinical disease correlates with organism burden and molecular assays yield quantitative data, we hypothesized that numerical cutoffs could be utilized to improve the specificity of the Luminex xTAG GI pathogen panel (GPP) for infection. Analysis of cotested liquid stool samples ( = 1,105) identified a GPP median fluorescence intensity (MFI) value cutoff of ≥1,200 to be predictive of two-step algorithm (2-SA; 96.4% concordance) and toxin enzyme immunoassay (EIA) positivity. Application of this cutoff to a second cotested data set ( = 1,428) yielded 96.5% concordance. To determine test performance characteristics, concordant results were deemed positive or negative, and discordant results were adjudicated via chart review. Test performance characteristics for the MFI cutoff of ≥150 (standard), MFI cutoff of ≥1,200, and 2-SA were as follows (respectively): concordance, 95, 96, and 97%; sensitivity, 93, 78, and 90%; specificity, 95, 98, and 98%; positive predictive value, 67, 82, and 81%;, and negative predictive value, 99, 98, and 99%. To capture the high sensitivity for organism detection (MFI of ≥150) and high specificity for active infection (MFI of ≥1,200), we developed and applied a reporting algorithm to interpret GPP data from patients ( = 563) with clinician orders only for syndromic panel testing, thus enabling accurate reporting of for 95% of samples (514 negative and 5 true positives) irrespective of initial clinical suspicion and without the need for additional testing.

Clinical interpretation of enteric molecular diagnostic tests

“…As Tilmanne et al [1] highlight, quantitative test results might distinguish DOI of original article: https://doi.org/10.1016/j.cmi.2019.07.021. pathogens causing active disease, such as the fluorescence-based method developed by Leal et al for C. difficile [11], but establishing cut-points for actionability requires considerable populationbased data. Detection of multiple pathogens is also common but highly variable [2,4e6].…”

Clinical evaluation of a non-purified direct molecular assay for the detection of Clostridioides difficile toxin genes in stool specimens

“…Several molecular assays for detection of toxin genes have been developed and are classified into three groups: those that detect tcdB gene for the diagnosis of CDI, including the BD MAX Cdiff assay [7], and the cobas Liat Cdiff assay [8]; those that detect cdt gene and tcdC mutations in addition to tcdB gene, including the Xpert C. difficile [9] assay and the Verigene CDF Panel [10]; and multiplex molecular assays such the FilmArray GI panel [11] and the xTAG Gastrointestinal Pathogen Panel [12]. Most molecular assays have been reported to have excellent performance for the detection of tcdB [7,13] and prompt identification was reported among several assays [14,15].…”

A high-throughput and multiplex microsphere immunoassay based on non-structural protein 1 can discriminate three flavivirus infections

“…With its high-throughput and multiplex (up to 100-plex) capacity, microsphere immunoassay (MIA) has been employed in the detection of cytokines, transplantation and transfusion antigens, and various bacterial and viral pathogens [40–43]. Previously, we reported that a combination of ELISAs based on the NS1 proteins of DENV and ZIKV can distinguish various DENV and ZIKV infections [44,45].…”