Ultrasensitive Detection of Clostridioides difficile Toxins in Stool by Use of Single-Molecule Counting Technology: Comparison with Detection of Free Toxin by Cell Culture Cytotoxicity Neutralization Assay.

Laboratory tests for Clostridioides difficile infection (CDI) rely on the detection of free toxin or molecular detection of toxin genes. The Singulex Clarity C. diff toxins A/B assay is a rapid, automated, and ultrasensitive assay that detects C. difficile toxins A and B in stool. We compared CDI assays across two prospective multicenter studies to set a cutoff for the Clarity assay and to independently validate the performance compared with that of a cell culture cytotoxicity neutralization assay (CCCNA). The cutoff was set by two sites testing fresh samples from 897 subjects with suspected CDI and then validated at four sites testing fresh samples from 1,005 subjects with suspected CDI. CCCNA testing was performed at a centralized laboratory. Samples with discrepant results between the Clarity assay and CCCNA were retested with CCCNA when the Clarity result agreed with that of at least one comparator method; toxin enzyme immunoassays (EIA), glutamate dehydrogenase (GDH) detection, and PCR were performed on all samples. The cutoff for the Clarity assay was set at 12.0 pg/ml. Compared to results with CCCNA, the Clarity assay initially had 85.2% positive agreement and 92.4% negative agreement. However, when samples with discrepant results between the Clarity assay and CCCNA in the validation study were retested by CCCNA, 13/17 (76.5%) Clarity-negative but CCCNA-positive samples (Clarity+/CCCNA-) became CCCNA-, and 5/26 (19.2%) Clarity+/CCCNA- samples became CCCNA+, resulting in a 96.3% positive agreement and 93.0% negative agreement between Clarity and CCCNA results. The toxin EIA had 59.8% positive agreement with CCCNA. The Clarity assay was the most sensitive free-toxin immunoassay, capable of providing CDI diagnosis in a single-step solution. A different CCCNA result was reported for 42% of retested samples, increasing the positive agreement between Clarity and CCCNA from 85.2% to 96.3% and indicating the challenges of comparing free-toxin results to CCCNA results as a reference standard.

Performance comparison of the cobas Liat and Cepheid GeneXpert systems for Clostridium difficile detection.

Clostridium difficile infection (CDI) is a high burden and significant cause of healthcare-acquired infectious diarrhea in the United States (US). Timely and accurate diagnosis of CDI enables the rapid initiation of antibiotic therapy and infection control policies to minimize disease transmission. Polymerase chain reaction (PCR) assays have become a preferred modality for diagnosing CDI in the US. The cobas Liat Cdiff PCR test is a novel assay that can be performed on-demand for hospital-based testing with a rapid 20-minute turnaround time from specimen collection to result reporting. We compared the clinical performance of the cobas Liat Cdiff test to the previously introduced Xpert C. difficile/Epi test; both tests are FDA-cleared PCR assays that detect the toxin B (tcdB) gene of C. difficile. Prospectively collected and remnant stool specimens from 310 patients with suspected CDI were obtained for analysis. The cobas Liat Cdiff and Xpert PCR tests showed an overall percent agreement of 97.4% (302/310; 95% CI: 95.0-98.9). Low bacterial burdens of toxigenic C. difficile, indicated by significantly delayed PCR cycle threshold (Ct) values, explained most of the discordance. Positive and negative percent agreement of the cobas Liat Cdiff test compared to the Xpert PCR test were 94.5% (52/55) and 98.0% (250/255), respectively. The clinical performance of the cobas Liat Cdiff test, combined with its simplicity of use and rapid result reporting, provides a reliable option for clinical laboratory use.

Clinical decision making in the emergency department setting using rapid PCR: Results of the CLADE study group.

BACKGROUND: Emergency Departments (ED) are challenged during influenza season by patients who present acutely during sporadic ED visits. ED management is largely empiric, often occurring without reliable diagnostics needed for targeted therapies, safe outpatient discharge, or hospital admissions. OBJECTIVE: To evaluate the impact of the influenza diagnosis on physician decision making during ED visits using the Cobas Liat® influenza A + B assay. STUDY DESIGN: Prospective study assessing the impact of rapid (<30 min), reverse-transcriptase polymerase chain reaction (RT-PCR) influenza testing on physician decision making in the ED. Physician responses established pre-and post-diagnosis management courses which required confirmation via secondary documentation in the medical record. Changes in physician decision making were analyzed across four clinical touchpoints: (i) admission/discharge status, (ii) medical procedures, (iii) antiviral and antibiotic prescribing, and (iv) laboratory studies. RESULTS: An influenza diagnosis changed patient management courses, relative to empiric, pre-diagnosis plans, in in 61% of the cases resulting in cost savings of $49,420-to-$42,270 over 143 patients and 104 days during influenza season resulting in a cost savings of $200.40/ED visit. Evaluation over 2000 ED patient visits projects cost savings > $578,000 due to deferred admissions, and reduction in antiviral prescribing. Sensitivity of ED-based influenza testing using the Cobas Liat® assay was equivalent to centralized lab testing at 98.8% sensitivity and 98.5% specificity respectively. CONCLUSION: Providing rapid, RT-PCR influenza testing to ED settings is actionable and used to guide patient care decisions. Understanding the cascade of events linked to the influenza diagnosis in the ED provides overall cost savings which offset the cost of providing ED-based testing.