Decreasing incidence of Staphylococcus aureus bacteremia over 9 years: greatest decline in community-associated methicillin-susceptible and hospital-acquired methicillin-resistant isolates.

BACKGROUND: The impact of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) emergence on the epidemiology of S aureus bacteremia (SAB) is not well documented. METHODS: This was an observational study of adult (aged ≥18 years) inpatients with SAB in a single 808-bed teaching hospital during 2002-2003, 2005-2006, 2008-2009, and 2010 with period-stratified SAB rate, onset mode, patient characteristics, and outcome. RESULTS: We encountered a total of 1,098 cases over the entire study period. The rate decreased steadily over time (from 6.64/10(3) discharges in 2002-2003 to 6.49/10(3) in 2005-2006, 5.24/10(3) in 2008-2009, and 5.00/10(3) in 2010; P = .0001), with a greater decline in community-associated cases (0.99/10(3), 0.77/10(3), 0.58/10(3), and 0.40/10(3), respectively; P = .0005) compared with health care-associated cases (5.65/10(3), 5.72/10(3), 4.66/10(3), and 4.60/10(3), respectively; P = .005). The decline was principally in MSSA (3.11/10(3), 2.21/10(3), 2.24/10(3), and 1.75/10(3), respectively; P = .00006), including both community-associated (P = .0002) and health care-associated cases (P = .006). Although overall rate changes in MRSA were not significant (P = .09), hospital-onset MRSA decreased markedly (P < .00001), whereas CA-MRSA increased (P = .03). The all-cause 100-day mortality rate did not change significantly (25.6% for 2002-2003, 25.2% for 2005-2006, 28.1% for 2008-2009, and 32.2% for 2010; P = .10). Differences in MSSA/MRSA-associated mortality decreased (20.1% vs 30.6%, P = .03 for 2002-2003; 18.1% vs 28.9%, P = .05 for 2005-2006; 21.7% vs 32.9%, P = .05 for 2008-2009; and 29.3% vs 34.9, P = .5 for 2010). CONCLUSIONS: SAB incidence is decreasing, with the greatest decline in community-associated MSSA and hospital-onset MRSA cases. Most health care-associated cases currently are community-onset. MRSA/MSSA-related mortality is comparable. These changes are likely related to the emergence of CA-MRSA and the inpatient-to-outpatient shift in health care.

Relevance of vancomycin-intermediate susceptibility and heteroresistance in methicillin-resistant Staphylococcus aureus bacteraemia.

OBJECTIVES: To assess the relevance of vancomycin-intermediate susceptibility (VISA) and heteroresistance (hVISA) in methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia. METHODS: We determined vancomycin MICs for 371 saved MRSA blood isolates (2002-03; 2005-06) by Etest and broth microdilution (BMD), screened for hVISA (Etest methods), determined the population analysis profile (PAP)/AUC for isolates with suspected reduced susceptibility (MICs >2 mg/L and/or hVISA-screen-positive versus Mu3 (hVISA control), and stratified patient characteristics and outcome according to susceptibility phenotype: VISA (PAP/AUC >1.3), hVISA (PAP/AUC 0.9-1.3), and susceptible (S-MRSA; PAP/AUC <0.9). RESULTS: PAP/AUC revealed 6 (1.6%) VISA and 30 (8.1%) hVISA phenotypes. The Etest MIC was above the susceptibility cut-off (2 mg/L) for all VISA isolates, whereas the BMD MIC was within the susceptibility range in two (33.3%) instances. Eight hVISA isolates (26.7%) with MICs of 2 mg/L were hVISA-screen negative. SCCmec typing revealed SCCmec II in 100% of VISA, 86.7% of hVISA and 75.5% of S-MRSA isolates (P = 0.04). Prior vancomycin use was documented in 100% of VISA, 73.3% of hVISA and 52.2% of S-MRSA cases (P = 0.002). Outcome (compared in 243 vancomycin-treated patients with MICs of 2 mg/L) revealed longer time to clearance in VISA cases [12.1 ±â€Š13.1 days versus 3.3 ±â€Š3.9 (hVISA) and 3.7 ±â€Š5.1 (S-MRSA); P = 0.001], more frequent endocarditis [33.3% versus 9.1% (hVISA; P = 0.1) and 4.2% (S-MRSA; P = 0.001)] and attributable mortality [33.3% versus 9.1% (hVISA; P = 0.1) and 8.4% (S-MRSA); P = 0.08]. CONCLUSIONS: No adverse outcome was documented with hVISA phenotype, whereas VISA contributed to vancomycin treatment failure. VISA and hVISA appear to emerge in SCCmec II isolates among vancomycin-exposed patients and are better detected by Etest.

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.

Prevalence of colonization with community-associated methicillin-resistant Staphylococcus aureus among end-stage renal disease patients and healthcare workers.

OBJECTIVE: To evaluate the prevalence, epidemiologic features, and molecular characteristics of colonization with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) among hospitalized dialysis patients and their healthcare workers (HCWs). DESIGN: Prospective observational clinical and laboratory study of nasal colonization. SETTING: A 600-bed urban academic medical center. SUBJECTS: One hundred twenty hospitalized dialysis inpatients and 100 HCWs. RESULTS: Of 120 patients, 40 (33%) were colonized with S. aureus; 26 (65%) of these 40 were colonized with MRSA. Among the 26 MRSA isolates, 10 (38.5%) carried staphylococcal cassette chromosome (SCC) mec type IV (ie, CA-MRSA), and 7 of these 10 carried the genes for the Panton-Valentine leukocidin (PVL) toxin. Patients colonized with healthcare-associated MRSA strains and those colonized with CA-MRSA strains were similar, except for a higher frequency of a history of congestive heart failure among those with healthcare-associated MRSA strains (P=.014). Among 10 patients who presented with or developed an S. aureus infection while hospitalized, 8 were colonized with S. aureus, 7 with MRSA, and 3 with SCCmec type IV strains. Among 100 HCWs, 31 were colonized with S. aureus, including 6 with MRSA; 2 of the MRSA isolates belonged to CA-MRSA strains, and soft-tissue infections were reported in one of the HCWs and in the family member of the other HCW colonized with these strains. CONCLUSIONS: There is a high rate of colonization with MRSA and CA-MRSA among hospitalized dialysis patients and their HCWs. As other studies have found, it appears that individuals are being colonized with both CA-MRSA strains and healthcare-associated MRSA strains.