Screening for Intermediately Vancomycin-Susceptible and Vancomycin-Heteroresistant Staphylococcus aureus by Use of Vancomycin-Supplemented Brain Heart Infusion Agar Biplates: Defining Growth Interpretation Criteria Based on Gold Standard Confirmation.

BHI agars supplemented with vancomycin 4 (BHI-V4) and 3 (BHI-V3) mg/liter have been proposed for screening vancomycin intermediately susceptible Staphylococcus aureus (VISA) and heteroresistant (hVISA) phenotypes, respectively, but growth interpretation criteria have not been established. We reviewed the growth results (CFU) during population analysis profile-area under the curve (PAP-AUC) of consecutive methicillin-resistant Staphylococcus aureus (MRSA) blood isolates, which were saved intermittently between 1996 and 2012. CFU counts on BHI-V4 and BHI-V3 plates were stratified according to PAP-AUC interpretive criteria: <0.90 (susceptible [S-MRSA]), 0.90 to 1.3 (hVISA), and >1.3 (VISA). CFU cutoffs that best predict VISA and hVISA were determined with the use of receiver operating characteristic (ROC) curves. Mu3, Mu50, and methicillin-susceptible S. aureus (MSSA) controls were included. We also prospectively evaluated manufacturer-made BHI-V3/BHI-V4 biplates for screening of 2010-2012 isolates. The PAP-AUC of 616 clinical samples was consistent with S-MRSA, hVISA, and VISA in 550 (89.3%), 48 (7.8%), and 18 (2.9%) instances, respectively. For VISA screening on BHI-V4, a cutoff of 2 CFU/droplet provided 100% sensitivity and 97.7% specificity. To distinguish VISA from hVISA, a cutoff of 16 CFU provided 83.3% sensitivity and 94.7% specificity; the specificity was lowered to 89.5% with a 12-CFU cutoff. For detecting hVISA/VISA on BHI-V3, a 2-CFU/droplet cutoff provided 98.5% sensitivity and 93.8% specificity. These results suggest that 2-CFU/droplet cutoffs on BHI-V4 and BHI-V3 best approximate VISA and hVISA gold standard confirmation, respectively, with minimal overlap in samples with borderline PAP-AUC. Simultaneous screening for VISA/hVISA on manufacturer-made BHI-V4/BHI-V3 biplates is easy to standardize and may reduce the requirement for PAP-AUC confirmation.

Decreasing prevalence of isolates with vancomycin heteroresistance and vancomycin minimum inhibitory concentrations ≥2 mg/L in methicillin-resistant Staphylococcus aureus over 11 years: potential impact of vancomycin treatment guidelines.

We evaluated vancomycin MIC (V-MIC) and the prevalence of intermediately susceptible (VISA) and heteroresistant (hVISA) isolates trends in methicillin-resistant Staphylococcus aureus bacteremia among 720 adults (≥ 18 years) inpatients over 4 study periods (2002-2003, 2005-2006, 2008-2009, and 2010-2012). V-MIC (Etest) and the prevalence of hVISA and VISA (determined by population analysis profile-area under the curve) were stratified according to the study period. Mean vancomycin MIC was 1.78 ± 0.39, 1.81 ± 0.47, 1.68 ± 0.26, and 1.54 ± 0.28 mg/L in 2002-2003, 2005-2006, 2008-2009, and 2010-2012, respectively (P < 0.0001). We noted a steadily decreasing prevalence of isolates with V-MIC ≥ 2 mg/L (50.0%, 45.2%, 35.4%, and 18.7%; P < 0.0001) and hVISA (9.7%, 6.6%, 3.0%, and 2.1%; P=0.0003). VISA prevalence remained low (0-2%). These changes coincided with steadily increasing vancomycin trough levels (9.9 ± 7.8, 11.1 ± 8.4, 16.6 ± 7.8, and 19.7 ± 5.9 mg/L in 2002-2003, 2005-2006, 2008-2009, and 2010-2012, respectively; P < 0.0001). These changes imply that adherence to vancomycin treatment guidelines may suppress the development of less susceptible isolates.

MALDI-TOF identification of Gram-negative bacteria directly from blood culture bottles containing charcoal: Sepsityper® kits versus centrifugation-filtration method.

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry has dramatically altered the way microbiology laboratories identify clinical isolates. Direct blood culture (BC) detection may be hampered, however, by the presence of charcoal in BC bottles currently in clinical use. This study evaluates an in-house process for extraction and MALDI-TOF identification of Gram-negative bacteria directly from BC bottles containing charcoal. Three hundred BC aliquots were extracted by a centrifugation-filtration method developed in our research laboratory with the first 96 samples processed in parallel using Sepsityper® kits. Controls were colonies from solid media with standard phenotypic and MALDI-TOF identification. The identification of Gram-negative bacteria was successful more often via the in-house method compared to Sepsityper® kits (94.7% versus 78.1%, P≤0.0001). Our in-house centrifugation-filtration method was further validated for isolation and identification of Gram-negative bacteria (95%; n=300) directly from BC bottles containing charcoal.

Lack of association of outcomes with treatment duration and microbiologic susceptibility data in Clostridium difficile infections in a non-NAP1/BI/027 setting.

BACKGROUND: Concerns regarding the poor response of severe Clostridium difficile infection (CDI) treated with metronidazole have arisen over the last 5 y. METHODS: We conducted a prospective, non-interventional study of CDI cases at our institution to evaluate the role of drug resistance, co-morbidities, and the emergence of hypervirulent strains on patient outcomes. A total of 118 adult inpatients with diarrhea and a positive stool for C. difficile toxin immunoassay had positive stool cultures and were included in the study. All 118 isolates had vancomycin and metronidazole susceptibility testing via the E-test method; rep-PCR was performed on 47 isolates. Of the 118 study patients, 107 were treated with either metronidazole or vancomycin. RESULTS: Initial therapy was metronidazole in 98.1% (n = 105) and vancomycin in 1.9% (n = 2) patients. Evaluable clinical response within 5 days of treatment was noted in 52.5% (52/99) of cases. The mean duration of treatment was 11.7 ± 7.2 days. The 30-day all-cause mortality rate was 24.6% (29/118). Recurrence occurred in 23.6% (21/89). A recent stay in the intensive care unit was associated with increased 30-day mortality (odds ratio 3.58, p = 0.012). There were no isolates resistant to metronidazole or vancomycin. Only 1 isolate was possibly related to the NAP1/BI/027 reference strain. No strain-related differences in deaths or recurrence were noted. CONCLUSIONS: Deaths related to CDI in our study appear to be related to multiple factors and did not appear to be independently related to antibiotic susceptibility, strain type, or treatment duration.

The effect of resident peer-to-peer education on compliance with urinary catheter placement indications in the emergency department.

OBJECTIVE This study aims to evaluate the effect of resident peer-to-peer education on knowledge of appropriate urinary catheter (UC) placement in the emergency department (ED) and to determine if this translates into further reduction in UC utilisation. Background Instituting guidelines for appropriate UC placement reduces UC utilisation in the ED. No study has explored if resident education in a teaching hospital would further reduce UC utilisation. METHODS An educational intervention implemented in February 2009 consisted of a lecture, distribution of pocket cards and a peer-administered weekly review of institutional UC guidelines. A 12-question multiple-choice test was given to residents prelecture and postlecture, and the 12-question test was repeated 3 months later. Retrospective chart review was performed to evaluate UC utilisation before, immediately after and 3 months after the educational intervention. RESULTS 30 residents completed all three tests. Significant differences were found between the mean test score pre-education and the mean test score immediately after education (9.43±1.17 vs 10.87±1.46, p<0.001) and between the mean test score pre-education and the mean test score 3 months posteducation (9.43±1.17 vs 10.43±1.28, p<0.001). There was no significant difference in UC utilisation or in the proportion of indicated UCs placed by residents within the three study periods. CONCLUSIONS Resident peer-to-peer education was associated with improvement of knowledge but did not result in decreased UC utilisation. A more active approach must be taken and other factors need to be further explored to reduce unnecessary placement of UC by residents in the ED.

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.

Urinary catheters in the emergency department: very elderly women are at high risk for unnecessary utilization.

BACKGROUND: Many of the urinary catheters (UCs) placed in the emergency department (ED) might not be necessary. We evaluated compliance with our institutional UC utilization guidelines and assessed factors influencing utilization. METHODS: We conducted a 12-week retrospective observational study evaluating UC utilization in all admissions from the ED. Data included reason for placement, presence of a physician's order for placement, resident physician involvement, and patient age and sex. RESULTS: Out of 4521 patients evaluated, 532 (11.8%) had a UC placed. Of these UCs, 371 (69.7%) were indicated, and 312 (58.6%) had a physician's order documented. The mean age of the patients who had a UC placed without an indication was 71.3 ± 18.8 years, that of patients with an indication was 60.0 ± 22.4 years (P < .0001), and that of patients who did not have a UC placed was 56.2 ± 22.6 years (P < .0001). Half of the women aged ≥80 years who had a UC placed did not have an indication according to our institutional guidelines. Multivariate logistic regression showed that women were 1.9 times more likely than men, and those age ≥80 years were 2.9 times more likely than those age ≤50 years, to have a UC placed without an indication. CONCLUSION: Very elderly women are at high risk for inappropriate UC utilization in the ED. Interventions are needed to address this vulnerable population.

Effect of establishing guidelines on appropriate urinary catheter placement.

OBJECTIVES: Avoiding placement of unnecessary urinary catheters (UCs) in the emergency department (ED) affects UC utilization during hospitalization. The authors sought to evaluate the effect of establishing institutional guidelines for appropriate UC placement coupled with emergency physician (EP) education on UC utilization. METHODS: Urinary catheter utilization was measured before and after the establishment of guidelines and EP education. Data collected included the presence of a UC on ED arrival, placement of a UC in the ED, documentation of a physician order for UC placement, reasons for placement, and compliance with the guidelines. Chi-square analyses were used to study the association between pre- and postintervention time periods and catheter use. RESULTS: A total of 377 (15%) patients had UCs; only 151 (47%) UCs initially placed in the ED had a physician order documented. UC placement was appropriately indicated in 75.5% of patients with a documented physician order, but in only 52% of cases without a documented physician order (p<0.001). The physician intervention was associated with an overall reduction in UC utilization from 16.4% to 13% (p=0.018). Physicians ordered 40% fewer UCs postintervention compared to preintervention. Preintervention, a physician order for UC placement was found indicated in 72.6% patients, compared to 82.2% patients with UC placed postintervention (p=0.21). CONCLUSIONS: Establishing guidelines for UC placement and physician education in the ED were associated with a marked reduction in utilization. However, addressing appropriate UC utilization may require evaluating other factors such as nursing influence on utilization.

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.

Role of SCCmec type in outcome of Staphylococcus aureus bacteremia in a single medical center.

Staphylococcus aureus virulence factors may determine infection presentation. Whether SCCmec type-associated factors play a role in S. aureus bacteremia is unclear. We conducted a prospective observation of adult inpatients with S. aureus bacteremia (1 November 2005 to 31 December 2006), performed SCCmec typing of methicillin-resistant S. aureus (MRSA) isolates, and stratified the results according to SCCmec type. We studied 253 patients. MRSA accounted for 163 (64.4%) cases. The illness severity index was similar in MRSA and methicillin-sensitive S. aureus (MSSA) cases. MRSA caused higher in-hospital mortality (23.9% versus 8.9%; P=0.003), longer bacteremia (4.7+/-6.5 days versus 2.7+/-2.9 days; P=0.01), but similar metastatic infection (14.7% versus 15.6%). Stratifying the results according to SCCmec type revealed significant differences. SCCmec type II caused highest mortality (33.3%) versus type IVa (13.5%), other MRSA (12.5%), and MSSA (8.9%). SCCmec IVa produced the highest metastatic infection (26.9% versus 9.1% [SCCmec II], 8.3% [other MRSA], and 15.6% [MSSA]). Persistent bacteremia (>or= 7 days) was similar in all SCCmec types (16.7 to 20.7%); each exceeded MSSA (6.7%; P=0.05). In multivariate analysis, SCCmec II was a predictor of mortality (odds ratio [OR]=3.73; 95% confidence interval [CI] = 1.81 to 7.66; P=0.009), SCCmec IVa was a predictor of metastatic infection (OR=3.52; CI=1.50 to 8.23; P=0.004), and MRSA (independent of SCCmec type) was a predictor of persistent bacteremia (OR=4.16; CI=1.47 to 11.73; P=0.007). These findings suggest that SCCmec-associated virulence factors play a role in the outcome of S. aureus bacteremia. Additional studies are needed to identify which virulence factors are the determinants of increased mortality with SCCmec type II and metastatic infection with SCCmec type IVa.

Staphylococcus aureus skin/soft-tissue infections: the impact of SCCmec type and Panton-Valentine leukocidin.

We assessed the role of Panton-Valentine leukocidin (PVL) and SCCmec type in community associated (CA) and healthcare associated (HC) Staphylococcus aureus (SA) skin/soft-tissue infections (STI). We prospectively monitored microbiology results (11 January 2005 to 6 January 2006), screened inpatients with SA in tissue samples or blood, and selected adults with STI. We recorded clinical/microbiological characteristics, and tested saved isolates for PVL genes (real time PCR) and SCCmec type (conventional multiplex PCR). We encountered 204 patients. MRSA strains that accounted for 70.5% CA and 66.0% HC cases, caused more abscesses (55.7% vs 29.7%; p =0.001) and were often PVL-positive (68.9% vs 4.8%; p <0.001). PVL-positive isolates caused more abscesses (72.9% vs 26.5%; p <0.001) but similar bacteremia (7.3% vs 7.1%). SCCmec IVa made up 95.8% of PVL-positive strains and accounted for 69.8% of the abscesses. SCCmec II caused higher mortality (14.8% vs 0-3.1%; p = 0.02). PVL was a predictor of abscesses (p <0.001). Predictors of bacteremia were age > or = 65 y (p =0.004), necrotizing infection (p =0.014), and head/neck location (p =0.05). These findings suggest that SCCmec type and PVL status influence STI manifestations and contribute to MRSA-MSSA differences. PVL is implicated in abscess formation but not bacteremia. Bacteremia is likely related to host condition and/or other virulence factors that were not studied.