Paul Riska

Comparison of BD GeneOhm Cdiff Real-Time PCR Assay with a Two-Step Algorithm and a Toxin A/B Enzyme-Linked Immunosorbent Assay for Diagnosis of Toxigenic Clostridium difficile Infection

ABSTRACT The BD GeneOhm Cdiff assay, a real-time PCR assay for the detection of the Clostridium difficile toxin B (tcdB) gene, was compared with the toxin A/B (Tox A/B) II enzyme-linked immunosorbent assay (ELISA) and a two-step algorithm which includes a C. Diff Chek-60 glutamate dehydrogenase (GDH) antigen assay followed by cytotoxin neutralization. Four hundred liquid or semisolid stool samples submitted for diagnostic C. difficile testing, 200 GDH antigen positive and 200 GDH antigen negative, were selected for analysis. All samples were tested by the C. Diff Chek-60 GDH antigen and cytotoxin neutralization assays, the Tox A/B II ELISA, and the BD GeneOhm Cdiff assay. Specimens with discrepant results were tested by toxigenic culture as an independent “gold standard.” Of 200 GDH-positive samples, 71 were positive by the Tox A/B II ELISA, 88 were positive by the two-step method, 93 were positive by PCR, and 96 were positive by the GDH antigen assay only. Of 200 GDH-negative samples, 3 were positive by PCR only. Toxigenic culture was performed for 41 samples with discrepant results, and 39 were culture positive. Culture resolution of discrepant results showed the Tox A/B II assay to have detected 70 (66.7%), the two-step method to have detected 87 (82.9%), and PCR to have detected 96 (91.4%) of 105 true positives. The BD GeneOhm Cdiff assay was more sensitive in detecting toxigenic C. difficile than the Tox A/B II assay (P < 0.0001); however, the difference between PCR and the two-step method was not significant (P = 0.1237). Enhanced sensitivity and rapid turnaround time make the BD GeneOhm Cdiff assay an important advance in the diagnosis of toxigenic C. difficile infection.

Loop-Mediated Isothermal Amplification Compared to Real-Time PCR and Enzyme Immunoassay for Toxigenic Clostridium difficile Detection

ABSTRACT Clostridium difficile infection is the primary cause of health care-associated diarrhea. While most laboratories have been using rapid antigen tests for detecting C. difficile toxins, they have poor sensitivity; newer molecular methods offer rapid results with high test sensitivity and specificity. This study was designed to compare the performances of two molecular assays (Meridian illumigene and BD GeneOhm) and two antigen assays (Wampole Quik Chek Complete and TechLab Tox A/B II) to detect toxigenic C. difficile. Fecal specimens from hospitalized patients (n = 139) suspected of having C. difficile infection were tested by the four assays. Nine specimens were positive and 109 were negative by all four methods. After discrepant analysis by toxigenic culture (n = 21), the total numbers of stool specimens classified as positive and negative for toxigenic C. difficile were 21 (15%) and 118 (85%), respectively. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were as follows: GeneOhm (95.2%, 100%, 100%, and 99.2%), illumigene (95.2%, 96.6%, 83.3%, and 99.2%), Tox A/B II (52.4%, 97.5%, 78.6%, and 92.4%), and Quik Chek Complete (47.6%, 100%, 100%, and 91.9%). The illumigene assay performed comparably to the GeneOhm assay with a slight decrease in test specificity; the sensitivities of both far exceeded those of the antigen assays. The clinical characteristics of the concordant and discrepant study patients were similar, including stool consistency and frequency. In the era of rapid molecular-based tests for toxigenic C. difficile, toxin enzyme immunoassays (EIAs) should no longer be considered the standard of care.

Effect of Algorithm-Based Therapy vs Usual Care on Clinical Success and Serious Adverse Events in Patients with Staphylococcal Bacteremia: A Randomized Clinical Trial

Importance The appropriate duration of antibiotics for staphylococcal bacteremia is unknown. Objective To test whether an algorithm that defines treatment duration for staphylococcal bacteremia vs standard of care provides noninferior efficacy without increasing severe adverse events. Design, Setting, and Participants A randomized trial involving adults with staphylococcal bacteremia was conducted at 16 academic medical centers in the United States (n = 15) and Spain (n = 1) from April 2011 to March 2017. Patients were followed up for 42 days beyond end of therapy for those with Staphylococcus aureus and 28 days for those with coagulase-negative staphylococcal bacteremia. Eligible patients were 18 years or older and had 1 or more blood cultures positive for S aureus or coagulase-negative staphylococci. Patients were excluded if they had known or suspected complicated infection at the time of randomization. Interventions Patients were randomized to algorithm-based therapy (n = 255) or usual practice (n = 254). Diagnostic evaluation, antibiotic selection, and duration of therapy were predefined for the algorithm group, whereas clinicians caring for patients in the usual practice group had unrestricted choice of antibiotics, duration, and other aspects of clinical care. Main Outcomes and Measures Coprimary outcomes were (1) clinical success, as determined by a blinded adjudication committee and tested for noninferiority within a 15% margin; and (2) serious adverse event rates in the intention-to-treat population, tested for superiority. The prespecified secondary outcome measure, tested for superiority, was antibiotic days among per-protocol patients with simple or uncomplicated bacteremia. Results Among the 509 patients randomized (mean age, 56.6 [SD, 16.8] years; 226 [44.4%] women), 480 (94.3%) completed the trial. Clinical success was documented in 209 of 255 patients assigned to algorithm-based therapy and 207 of 254 randomized to usual practice (82.0% vs 81.5%; difference, 0.5% [1-sided 97.5% CI, −6.2% to ∞]). Serious adverse events were reported in 32.5% of algorithm-based therapy patients and 28.3% of usual practice patients (difference, 4.2% [95% CI, −3.8% to 12.2%]). Among per-protocol patients with simple or uncomplicated bacteremia, mean duration of therapy was 4.4 days for algorithm-based therapy vs 6.2 days for usual practice (difference, −1.8 days [95% CI, −3.1 to −0.6]). Conclusions and Relevance Among patients with staphylococcal bacteremia, the use of an algorithm to guide testing and treatment compared with usual care resulted in a noninferior rate of clinical success. Rates of serious adverse events were not significantly different, but interpretation is limited by wide confidence intervals. Further research is needed to assess the utility of the algorithm. Trial Registration ClinicalTrials.gov Identifier: NCT01191840

Two for the price of one: emerging carbapenemases in a returning traveller to New York City

We report a case of a complex orthopaedic infection in a patient returning to New York City from Bangladesh where he was involved in a serious motor vehicle accident. He developed extensive osteomyelitis with a carbapenem-resistant Klebsiella pneumoniae. The isolate was unique due to the coexistence of New Delhi metallo-β-lactamase-1 and Oxacillinase type-181 carbapenemases, which are relatively uncommon in North America and were presumably acquired in Bangladesh. Herein, we explore challenges associated with management of carbapenem-resistant Enterobacteriaceae infections, including limited available data on effective antimicrobial therapy. We also highlight the added value of rapid diagnostic technology in guiding clinical management. Ultimately, the patient required both aggressive surgical management and combination therapy with aztreonam and ceftazidime-avibactam for true source control and favourable clinical outcome.

The Emperor’s New Clothes: Prospective Observational Evaluation of the Association between the Day 2 Vancomycin Exposure and Failure Rates among Adult Hospitalized Patients with MRSA Bloodstream Infections (PROVIDE)

Abstract Background Current guidelines recommend vancomycin (VAN) dosing to achieve AUC/MIC ratio ≥400 for patients (pts) with serious MRSA bloodstream infections (BSI), but supporting data were largely derived in single center retrospective studies. A recent study using a Bayesian approach to estimate the VAN AUC found that patients with MRSA BSI who had an AUCDAY2/MICBMD ≥ 650 or an AUCDAY2/MICETEST ≥ 320 had lower incidences of failure (Clin Infect Dis 59:666, 2014). This study prospectively evaluated if these VAN AUCDAY2/MIC targets were associated with lower incidences of failure (PROVIDE, Award number UM1AI104681, Antibacterial Resistance Leadership Group). Methods Prospective, multi-center (n = 14), observational study (2014–2106) of hospitalized adults with confirmed MRSA BSI treated with VAN ≥ 72h. Exclusion: (1) neutropenia; (2) cystic fibrosis; (3) renal replacement therapy; (4) APACHE-II score > 25; (5) previous MRSA BSI within 60 days. VAN exposures were estimated using maximum a posteriori probability procedure in ADAPT 5. MICBMD and MICETEST were performed at a central laboratory. Outcomes: failure (30-day mortality or MRSA BSI ≥ 7 days); acute kidney injury (AKI), ≥1.5 × increase in serum creatinine (Scr) among patients with a baseline SCR < 2.0mg/dl. The study was powered at 80% to detect a 17.5% difference in failure between AUCDAY2/MIC groups. Results Among the 265 evaluable patients, mean (SD) age was 61 (17) and APACHE-II was 12 (6). Endocarditis was definite/possible in 29%. The MIC50/90 by BMD and ETEST were 1/1 and 1.5/1.5mg/l, respectively. Failure occurred in 18%; 26% had AKI. Mean (SD) VAN duration was 18 (14) days. Mean (SD) AUCDAY2 was 586.9 (235.5) and 44% and 73% of patients achieved an AUCDAY2/MICBMD ≥ 650 and AUCDAY2/MICETEST ≥ 320. In the multivariate analyses (Figure 1), failure was not significantly different between AUCDAY2/MIC groups. In contrast, AKI was significantly more common in patients with an AUCDAY2/ MICETEST > = 320. Conclusion Achievement of higher VAN AUCDAY2/MIC exposures for patients with MRSA BSIs were not associated with better outcomes and were found to result in increased AKI. Clinicians should assess the benefits vs. risks of using VAN regimens that confer high AUCDAY2/MIC exposures for patients with MRSA BSIs. Disclosures T. P. Lodise Jr., allergan: Consultant, Grant Investigator, Scientific Advisor and Speaker’s Bureau, Consulting fee and Speaker honorarium; medicines company: Consultant, Grant Investigator, Scientific Advisor and Speaker’s Bureau, Consulting fee, Research support and Speaker honorarium; melinta: Consultant, Consulting fee; motif: Consultant and Scientific Advisor, Consulting fee; paratek: Consultant and Scientific Advisor, Consulting fee; nabriva: Consultant, Consulting fee; M. J. Zervos, Merck, Inc.: Investigator, Research grant; M. Scheetz, Bayer: Scientific Advisor, Consulting fee; V. Fowler Jr., Pfizer, Novartis, Galderma, Novadigm, Durata, Debiopharm, Genentech, Achaogen, Affinium, Medicines Co., Cerexa, Tetraphase, Trius, MedImmune, Bayer, Theravance, Cubist, Basilea, Affinergy, Janssen, xBiotech, Contrafect: Consultant, Consulting fee; NIH, Basilea, MedImmune, Cerexa/Forest/Actavis/Allergan, Pfizer, Advanced Liquid Logics, Theravance, Novartis, Cubist/Merck; Medical Biosurfaces; Locus; Affinergy; Contrafect; Karius: Grant Investigator, Research grant; Green Cross, Cubist, Cerexa, Durata, Theravance; Debiopharm: Consultant, Consulting fee; UpToDate: author on several chapters, Royalties