title: Comparison of method-specific vancomycin minimum inhibitory concentration values and their predictability for treatment outcome of meticillin-resistant Staphylococcus aureus (MRSA) infections.
abstract: The objectives of this study were to examine the predictive value of method-specific vancomycin (VAN) minimum inhibitory concentration (MIC) results on treatment outcomes of meticillin-resistant Staphylococcus aureus (MRSA) infections. VAN MIC values for MRSA strains were determined using Etest, VITEK-1, MicroScan (MScan) and broth microdilution (BMD), with additional screening for heterogeneous glycopeptide-intermediate S. aureus (hGISA) phenotype. Patients' charts were reviewed for outcome correlation. Performance characteristics of method-specific VAN MICs in predicting outcome were compared. Most (76%) of the 92 strains tested caused pneumonia or bacteraemia. The majority of strains tested (>70%) had a VAN MIC >1mg/L by Etest or MScan compared with 41% by Vitek and 7% by BMD. Agreement between test methods for high versus low MICs (>1mg/L vs. < or = 1mg/L) ranged from 36% to 71%. High versus low VAN MICs by Etest differentiated response of invasive strains to VAN. Performance characteristics (sensitivity/specificity/positive predictive value/negative predictive value) were: Etest, 55/81/89/38%; and Vitek, 56/62/81/32/%, respectively. Eight strains (9%) demonstrated a hGISA phenotype; more yielded high MICs by Etest, MScan and Vitek than BMD (87%, 87% and 75% vs. 50%). In conclusion, VAN MIC testing methods produce highly variable results. The Etest method appears to be relatively more reliable in predicting treatment response and yielded higher MICs for strains with a hGISA phenotype.
authors.affiliation: Western University of Health Sciences, College of Pharmacy, 309 E. Second Street, Pomona, CA, USA.
authors.forename: Donald I
authors.initials: DI
authors.lastname: Hsu
authors.forename: Levita K
authors.initials: LK
authors.lastname: Hidayat
authors.forename: Ryan
authors.initials: R
authors.lastname: Quist
authors.forename: Janet
authors.initials: J
authors.lastname: Hindler
authors.forename: Asa
authors.initials: A
authors.lastname: Karlsson
authors.forename: Anne
authors.initials: A
authors.lastname: Yusof
authors.forename: Annie
authors.initials: A
authors.lastname: Wong-Beringer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use*; D015331:Cohort Studies; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000379:methods*; D008875:Middle Aged; D010641:Phenotype; D011237:Predictive Value of Tests; D011446:Prospective Studies; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D016896:Treatment Outcome; D014640:Vancomycin / Q000494:pharmacology* / Q000627:therapeutic use*; D020713:Vancomycin Resistance; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin