Vancomycin MIC plus heteroresistance and outcome of methicillin-resistant Staphylococcus aureus bacteremia: trends over 11 years.
Vancomycin MICs (V-MIC) and the frequency of heteroresistant vancomycin-intermediate Staphylococcus aureus (hVISA) isolates are increasing among methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) isolates, but their relevance remains uncertain. We compared the V-MIC (Etest) and the frequency of hVISA (Etest macromethod) for all MRSA blood isolates saved over an 11-year span and correlated the results with the clinical outcome. We tested 489 isolates: 61, 55, 187, and 186 isolates recovered in 1996-1997, 2000, 2002-2003, and 2005-2006, respectively. The V-MICs were < or = 1, 1.5, 2, and 3 microg/ml for 74 (15.1%), 355 (72.6%), 50 (10.2%), and 10 (2.1%) isolates, respectively. We detected hVISA in 0/74, 48/355 (13.5%), 15/50 (30.0%), and 8/10 (80.0%) isolates with V-MICs of < or = 1, 1.5, 2, and 3 microg/ml, respectively (P < 0.001). The V-MIC distribution and the hVISA frequency were stable over the 11-year period. Most patients (89.0%) received vancomycin. The mortality rate (evaluated with 285 patients for whose isolates the trough V-MIC was > or = 10 microg/ml) was comparable for patients whose isolates had V-MICs of < or = 1 and 1.5 microg/ml (19.4% and 27.0%, respectively; P = 0.2) but higher for patients whose isolates had V-MICs of > or = 2 microg/ml (47.6%; P = 0.03). However, the impact of V-MIC and hVISA status on mortality or persistent (> or = 7 days) bacteremia was not substantiated by multivariate analysis. Staphylococcal chromosome cassette mec (SCCmec) typing of 261 isolates (including all hVISA isolates) revealed that 93.0% of the hVISA isolates were SCCmec type II. These findings demonstrate that the V-MIC distribution and hVISA frequencies were stable over an 11-year span. A V-MIC of > or = 2 microg/ml was associated with a higher rate of mortality by univariate analysis, but the relevance of the V-MIC and the presence of hVISA remain uncertain. A multicenter prospective randomized study by the use of standardized methods is needed to evaluate the relevance of hVISA and determine the optimal treatment of patients whose isolates have V-MICs of > or = 2.0 microg/ml.
Department of Medicine, Infectious Diseases, St. John Hospital and Medical Center, Detroit, MI, USA.
Adina C
AC
Musta
Kathleen
K
Riederer
Stephen
S
Shemes
Patrick
P
Chase
Jinson
J
Jose
Leonard B
LB
Johnson
Riad
R
Khatib
D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D016470:Bacteremia / Q000188:drug therapy* / Q000382:microbiology*; D015373:Bacterial Typing Techniques; D002876:Chromosomes, Bacterial / Q000235:genetics; D016000:Cluster Analysis; D016172:DNA Fingerprinting; D005838:Genotype; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology* / Q000401:mortality; D016896:Treatment Outcome; D020713:Vancomycin Resistance
D000900:Anti-Bacterial Agents