title: Evaluation of the Xpert Carba-R (Cepheid) Assay Using Contrived Bronchial Specimens from Patients with Suspicion of Ventilator-Associated Pneumonia for the Detection of Prevalent Carbapenemases.
abstract: There is a critical need for rapid diagnostic methods for multidrug-resistant (MDR) pathogens in patients with a suspicion of ventilator-associated pneumonia (VAP). The Xpert Carba-R detects 5 targets for carbapenemase-producing organisms (blaKPC, blaNDM, blaVIM, blaOXA-48, and blaIMP-1). Our objective was to evaluate the performance of this assay directly on bronchial aspirates and to correlate the cycle number for a positive result (Ct) with the bacterial count. Bronchial aspirates from patients with a suspicion of VAP were spiked with a dilution of 1 of 4 MDR organisms carrying the resistance genes detected by the test prepared to a final concentration of 102-105 cfu/mL. We used a ROC curve and provided areas under the curve (AUC) with their 95% confidence intervals (CI). A point of maximum sensitivity (Se) and specificity (Sp) was derived and validity indices were calculated. One hundred contrived tests were performed. Se and Sp were 100% for all bacterial counts. A positive sample with a Ct ≤24.7 corresponded to a count ≥105 cfu/mL; if the Ct was within the range >24.7-≤26.9, this corresponded to a count ≥104 cfu/mL. When the Ct was >26.9, this corresponded to a count <104 cfu/mL. The Xpert Carba-R detects carbapenemase-producing organisms directly in contrived bronchial aspirates. Still, an important issue to consider is that the number of gene copies may vary according to many factors in vivo. If confirmed in further studies, the strong correlation observed between Ct values and the results of semiquantitative cultures suggests this test could serve to differentiate between infection and colonization in routine clinical practice.
authors.affiliation: Clinical Microbiology and Infectious Diseases Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.|Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.|Medicine Department, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Almudena
authors.initials: A
authors.lastname: Burillo
authors.affiliation: Clinical Microbiology and Infectious Diseases Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.|Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.|Medicine Department, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain.|CIBER de Enfermedades Respiratorias (CIBERES CB06/06/0058), Madrid, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Marín
authors.affiliation: Clinical Microbiology and Infectious Diseases Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.|Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.|Medicine Department, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain.|CIBER de Enfermedades Respiratorias (CIBERES CB06/06/0058), Madrid, Spain.
authors.forename: Emilia
authors.initials: E
authors.lastname: Cercenado
authors.affiliation: Microbiology Department, Hospital Universitario La Paz, Madrid, Spain.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Ruiz-Carrascoso
authors.affiliation: Department of Anesthesiology, Cardiac Surgery Intensive Care Unit, Hospital General Universitario Gregorio Marañón, Madrid, Spain.|CIBER de Enfermedades Respiratorias (CIBERES CB06/06/0058), Madrid, Spain.
authors.forename: María Jesús
authors.initials: MJ
authors.lastname: Pérez-Granda
authors.affiliation: Antibiotic Laboratory, Bacteriology Department, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Majadahonda, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: Oteo
authors.affiliation: Clinical Microbiology and Infectious Diseases Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.|Instituto de Investigación Sanitaria Gregorio Marañón, Madrid, Spain.|Medicine Department, School of Medicine, Universidad Complutense de Madrid, Madrid, Spain.|CIBER de Enfermedades Respiratorias (CIBERES CB06/06/0058), Madrid, Spain.
authors.forename: Emilio
authors.initials: E
authors.lastname: Bouza
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis*; D018432:Drug Resistance, Multiple; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology / Q000302:isolation & purification*; D004756:Enterobacteriaceae Infections / Q000175:diagnosis*; D057075:Enzyme Assays / Q000379:methods / Q000592:standards*; D006801:Humans; D025202:Molecular Diagnostic Techniques / Q000379:methods; D053717:Pneumonia, Ventilator-Associated / Q000175:diagnosis / Q000382:microbiology*; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000032:analysis*
chemical_list: D001426:Bacterial Proteins; D001618:beta-Lactamases; C063912:carbapenemase