ABSTRACT
Clostridium difficile-associated diarrhea is a well-recognized complication of antibiotic use. Historically, diagnosing C. difficile has been difficult, as antigen assays are insensitive and culture-based methods require several days to yield results. Nucleic acid amplification tests (NAATs) are quickly becoming the standard of care. We compared the performance of two automated investigational/research use only (IUO/RUO) NAATs for the detection of C. difficile toxin genes, the IMDx C. difficile for Abbott m2000 Assay (IMDx) and the BD Max Cdiff Assay (Max). A prospective analysis of 111 stool specimens received in the laboratory for C. difficile testing by the laboratory's test of record (TOR), the BD GeneOhm Cdiff Assay, and a retrospective analysis of 88 specimens previously determined to be positive for C. difficile were included in the study. One prospective specimen was excluded due to loss to follow-up discrepancy analysis. Of the remaining 198 specimens, 90 were positive by all three methods, 9 were positive by TOR and Max, and 3 were positive by TOR only. One negative specimen was initially inhibitory by Max. The remaining 95 specimens were negative by all methods. Toxigenic C. difficile culture was performed on the 12 discrepant samples. True C. difficile-positive status was defined as either positive by all three amplification assays or positive by toxigenic culture. Based on this definition, the sensitivity and specificity were 96.9% and 95% for Max and 92.8% and 100% for IMDx. In summary, both highly automated systems demonstrated excellent performance, and each has individual benefits, which will ensure that they will both have a niche in clinical laboratories.
Subject(s)
Biological Assay/methods , Clostridioides difficile/genetics , Clostridium Infections/diagnosis , Molecular Diagnostic Techniques/methods , Bacterial Proteins/genetics , Bacterial Toxins/genetics , Clostridium Infections/microbiology , Diarrhea/diagnosis , Diarrhea/microbiology , Enterotoxins/genetics , Feces/microbiology , Humans , Nucleic Acid Amplification Techniques/methods , Prospective Studies , Reagent Kits, Diagnostic , Retrospective Studies , Sensitivity and SpecificityABSTRACT
BACKGROUND: Reactivation of latent polyomavirus BK is associated with nephropathy (PVAN) after renal transplantation. BK viral load determinations are a highly sensitive and specific method for predicting risk for PVAN. OBJECTIVES AND STUDY DESIGN: The performance of three real-time PCR for BKV DNA quantification (MultiCode(®)-RTx BK virus ASR [MC-RTx], MGB-Alert BKV ASR [MGB] and a laboratory developed assay [LDA]) were evaluated against a conventional PCR (test of record, TOR) in terms of linearity, dynamic range, and accuracy. RESULTS: The LOD (log(10) copies/ml) were 2.0, 2.0 and 3.0 for MC-RTx, MGB and LDA, respectively with a commercial plasma panel and 2.0, 2.6 and 3.5 with a urine panel. These assays demonstrated excellent linearity (r(2) = 1.0) and reproducibility (CV range = 0.7-20.4%, 0.9-13.2%, and 0.5-13%, respectively). In an analysis of 100 clinical specimens, all 76 samples defined as true positive for BKV DNA (positive by two or more methods or a recent history of positivity) were detected with MC-RTx, while only 64 were detected with MGB and 55 were detected with LDA. BKV DNA was not detected by any method in the true negative specimens. Based on these results, the sensitivities were 100% for MC-RTx, 84% for MGB and 72% for LDA. The greatest linear correlation with the mean concentration was observed with MC-RTx (r(2) = 0.96) with two samples (3%) with greater than 0.5 log(10) variance in quantification versus seven (11%) with MGB and ten (18%) with LDA. CONCLUSIONS: These real-time assays for BKV load demonstrated excellent performance characteristics, with the MC-RTx demonstrating the greatest sensitivity.
