We sought here to review the present definition of catheter-related bloodstream infections (CR-BSI) due to coagulase-negative staphylococci (CNS) by comparing the routine phenotypic methods with a genotypic procedure that considers different morphotypes. Our phenotypic characterization of CNS isolates included routine identification with biotype and antibiotype. The genotypic diagnosis was based on longer incubation periods with the consideration of all morphotypes and molecular typing by pulsed-field gel electrophoresis techniques. We prospectively selected 61 episodes of suspected CR-BSI by CNS occurring during 1 year, based on the presence of a compatible clinical setting and the isolation of one or more CNS from blood and catheter tip. Of these episodes, 47 (77%) were identified as true episodes of CR-BSI based on the presence of microorganisms of the same genotype in the blood and on the catheter tip. The sensitivity, specificity, positive predictive, negative predictive, accuracy, positive likelihood ratio, and negative likelihood ratio values obtained by different phenotypic microbiological approaches to establish the diagnosis of CR-BSI were as follows: identity at species level (78. Catheter-related bloodstream infections (CR-BSI) are the main cause of documented sepsis (4, 5) in modern hospitals (2,20,27) and are mainly produced by coagulase-negative staphylococci (CNS) (6,26,32). The confirmed definition of a CR-BSI requires the isolation of one or more identical microorganism/s from blood and the catheter tip (19). However, present definitions are far from clear regarding the demonstration of such identity, particularly in the case of CNS. Most CNS colonies look alike after 24-h incubation, and laboratory routine involves taking a single colony for identification and antimicrobial susceptibility tests from those CNS growing in blood and on catheter tip cultures. The identity of both isolates is usually established on a phenotypic basis when the same genus, species, and antibiotype of the isolates in both samples are present. It is well known, however, that CNS growing on catheter tips may be frequently polyclonal (6, 12), especially when colonies are observed after longer periods of incubation. Moreover, biotype and antibiotype may have a weak correlation with genotype in CNS (22,30,34).7%We compare here the yields of two procedures for the characterization of CNS CR-BSI: "phenotypic" characterization, carried out in microbiology laboratories on a daily basis, and a procedure by which the different morphotypes are obtained after prolonged incubation and the application of genotyping with molecular techniques.
MATERIALS AND METHODS
Selection of Patients with CR-BSI.During a one-year period, we prospectively selected all consecutive patients fulfilling the following criteria: (i) age of Ն18 years; (ii) clinical signs of nosocomial sepsis (patients who had been in the hospital for more than 48 h when the first episode of fever was recorded and with one or more of the following signs or symptoms: tempera...
