Penicillin plus Ceftriaxone versus Ampicillin plus Ceftriaxone Synergistic Potential against Clinical Enterococcus faecalis Blood Isolates.

Penicillin plus ceftriaxone is a promising alternative to ampicillin plus ceftriaxone for the treatment of Enterococcus faecalis infective endocarditis. Limited data is available supporting the utilization of penicillin plus ceftriaxone. A total of 20 E. faecalis isolates; one wild-type strain (JH2-2) and 19 clinical blood strains were assessed for penicillin plus ceftriaxone and ampicillin plus ceftriaxone synergy using a 24-h time-kill experiment. Susceptibility was determined by broth microdilution. Differences in bactericidal, bacteriostatic, or inactivity, as well as synergy between treatments were assessed by chi-square or Fisher exact test. All E. faecalis isolates were considered susceptible to ampicillin and penicillin. Ampicillin plus ceftriaxone versus penicillin plus ceftriaxone similarly demonstrated synergy. Bactericidal activity was more commonly observed for ampicillin plus ceftriaxone versus penicillin plus ceftriaxone. Among isolates with a penicillin MIC of 4 µg/mL (n = 7), synergistic activity for both combinations was less common compared to isolates with a penicillin MIC ≤ 2 µg/mL (n = 13). Ampicillin plus ceftriaxone and penicillin plus ceftriaxone demonstrate similar synergistic potential against E. faecalis clinical blood isolates, but strains with higher penicillin and ceftriaxone MICs less frequently demonstrated synergy. Further research is warranted to determine the role of the penicillin plus ceftriaxone therapy and the penicillin MIC in clinical practice. IMPORTANCE Penicillin plus ceftriaxone demonstrates similar synergistic activity against Enterococcus faecalis to ampicillin plus ceftriaxone. Isolates with a penicillin MIC of 4 mg/L and a ceftriaxone MIC of 512 or higher, lack penicillin plus ceftriaxone synergy despite the penicillin susceptibility MIC breakpoint of 8 mg/L.

Multicenter Cohort Study of Ceftaroline Versus Daptomycin for Treatment of Methicillin-Resistant Staphylococcus aureus Bloodstream Infection.

BACKGROUND: Observational data suggest ceftaroline may be effective for methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI), but comparative data with standard of care are limited. This analysis compares the outcomes of MRSA BSI treated with ceftaroline or daptomycin. METHODS: Multicenter, retrospective, observational cohort study of adult patients with MRSA BSI from 2010 to 2017. Patients treated with ≥72 hours of ceftaroline or daptomycin were included. Those clearing BSI before study drug and those with a pneumonia source were excluded. The primary outcome was composite treatment failure, defined as 30-day mortality, BSI duration ≥7 days on study drug, and 60-day MRSA BSI recurrence. Inverse probability of treatment weighted risk difference in composite failure between daptomycin and ceftaroline groups was computed and 15% noninferiority margin applied. RESULTS: Two hundred seventy patients were included; 83 ceftaroline and 187 daptomycin. Ceftaroline was noninferior to daptomycin with respect to composite failure (39% daptomycin, 32.5% ceftaroline; weighted risk difference, 7.0% [95% confidence interval, -5.0% to 19.0%]). No differences between treatment groups was observed for 30-day mortality or other secondary efficacy outcomes. Creatine phosphokinase elevation was significantly more common among daptomycin patients (5.3% vs 0%, P = .034). Rash was significantly more common among ceftaroline patients (10.8 vs 1.1%, P = .001). CONCLUSIONS: No difference in treatment failure or mortality was observed between MRSA BSI treated with ceftaroline or daptomycin. These data support future study of ceftaroline as a primary MRSA BSI treatment and current use of ceftaroline when an alternative to vancomycin and daptomycin is required.

Optimizing outcomes using vancomycin therapeutic drug monitoring in patients with MRSA bacteremia: trough concentrations or area under the curve?

BACKGROUND: Vancomycin therapeutic drug monitoring is routinely performed but the specific measure used in practice is variable. OBJECTIVE: To evaluate the relationship between the first measured vancomycin trough, area-under-the-curve (AUC), and failure in patients with MRSA bacteremia. METHODS: This retrospective, cohort study included adult non-neutropenic patients with MRSA bacteremia who received vancomycin. The primary outcome was treatment failure. Initial trough and AUC values were compared between the failure and success groups. Classification and regression tree analysis was used to identify thresholds associated with failure. Multivariate analysis was performed to control for identified confounders. RESULTS: There were 89 patients. Failure occurred in 23 (26%). Trough and AUC values associated with failure were < 10.6 mg/L (39% vs. 13%; P = 0.006) and AUC < 410mg*h/L (40% vs. 17%; P = 0.014). Both remained significant after controlling covariates (trough < 10.6 mg/L, OR [95% CI] = 4.91 [1.6-15]; AUC<410mg*h/L, OR [95% CI] = 3.13 [1.14-8.62]). Only AUC was predictive of nephrotoxicity. CONCLUSION: Failure was more common with troughs < 10.6 mg/L or AUC < 410 mg*h/L. Supratherapeutic AUCs, but not trough, were associated with nephrotoxicity.

Glycopeptide Hypersensitivity and Adverse Reactions.

Glycopeptides, such as vancomycin and teicoplanin, are primarily used in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections, such as cellulitis, endocarditis, meningitis, pneumonia, and septicemia, and are some of the most commonly prescribed parenteral antimicrobials. Parenteral glycopeptides are first-line therapy for severe MRSA infections; however, oral vancomycin is used as a first-line treatment of Clostridioides difficile infections. Also, we currently have the longer-acting lipoglycopeptides, such as dalbavancin, oritavancin, and telavancin to our armamentarium for the treatment of MRSA infections. Lastly, vancomycin is often used as an alternative treatment for patients with ß-lactam hypersensitivity. Common adverse effects associated with glycopeptide use include nephrotoxicity, ototoxicity, and Redman Syndrome (RMS). The RMS is often mistaken for a true allergy; however, it is a histamine-related infusion reaction rather than a true immunoglobulin E (IgE)-mediated allergic reaction. Although hypersensitivity to glycopeptides is rare, both immune-mediated and delayed reactions have been reported in the literature. We describe the various types of glycopeptide hypersensitivity reactions associated with glycopeptides and lipoglycopeptides, including IgE-mediated reactions, RMS, and linear immunoglobulin A bullous dermatosis, as well as describe cross-reactivity with other glycopeptides.

The Emerging Role of ß-Lactams in the Treatment of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections.

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) are associated with substantial morbidity and mortality. Monotherapy with first-line antimicrobials such as vancomycin (VAN; glycopeptide) and daptomycin (DAP; lipopeptide) are inadequate in some cases due to reduced antibiotic susceptibilities or therapeutic failure. In recent years, ß-lactam antibiotics have emerged as a potential option for combination therapy with VAN and DAP that may meet an unmet therapeutic need for MRSA BSI. Ceftaroline (CPT), the only commercially available ß-lactam in the United States with intrinsic in vitro activity against MRSA, has been increasingly studied in the setting of VAN and DAP failures. Novel combinations of first-line agents (VAN and DAP) with ß-lactams have been the subject of many recent investigations due to in vitro findings such as the "seesaw effect," where ß-lactam susceptibility may be improved in the presence of decreased glycopeptide and lipopeptide susceptibility. The combination of CPT and DAP, in particular, has become the focus of many scientific evaluations, due to intrinsic anti-MRSA activities and potent in vitro synergistic activity against various MRSA strains. This article reviews the available literature describing these innovative therapeutic approaches for MRSA BSI, focusing on preclinical and clinical studies, and evaluates the potential benefits and limitations of each strategy.

Utilization of Augmented Renal Clearance in Trauma Intensive Care Scoring System to Improve Vancomycin Dosing in Trauma Patients at Risk for Augmented Renal Clearance.

Background: The Augmented Renal Clearance in Trauma Intensive Care (ARCTIC) scoring system is a validated system to predict augmented renal clearance in trauma patients. This study examined the ability of the ARCTIC score to identify patients at risk for subtherapeutic vancomycin trough concentrations relative to estimated creatinine clearance (eCrCl) alone. Methods: Trauma patients admitted to the intensive care unit from September 2012 to December 2017 who received vancomycin and had a vancomycin trough concentration recorded were included. Patients were excluded if their serum creatinine concentration was >1.3 mg/dL, if they had received vancomycin doses <30 mg/kg per day, an improperly timed trough concentration measurement, or renal replacement therapy. The primary endpoint was an initial subtherapeutic vancomycin trough concentration (<10 mg/L). Classification and regression tree (CART) analysis was used to identify thresholds for the ARCTIC score and other continuous data where subtherapeutic troughs were more common. A step-wise logistic regression analysis was performed to control for confounders for subtherapeutic troughs whereby inclusion of ARCTIC was modeled sequentially after eCrCl. Results: A total of 119 patients with a mean age of 42 ± 17 years and eCrCl 142 ± 39 mL/min met the inclusion criteria. The mean daily vancomycin dose was 44 ± 9 mg/kg, and the incidence of subtherapeutic trough concentration was 46%. The CART analysis identified two variables creating three groups where subtherapeutic trough concentrations differed: eCrCl >105 mL/min and ARCTIC score ≥7, eCrCl >105 mL/min and ARCTIC score <7, and eCrCl ≤105 mL/min. The base logistic regression model identified eCrCl >105 mL/min and pelvic fracture as risk factors for subtherapeutic trough values. The final model included the addition of ARCTIC score ≥7, which improved the model significantly (p = 0.009). Predictors of subtherapeutic trough concentrations were (odds ratio [95% confidence interval]): eCrCl >105 mL/min (6.5 [1.66-25.07]), ARCTIC score ≥7 (3.26 [1.31-8.09]), and pelvic fracture (4.36 [1.27-14.93]). Conclusion: The ARCTIC score is useful when applied in conjunction with eCrCl. Patients with a eCrCl >105 mL/min and an ARCTIC score ≥7 may require a more aggressive dosing strategy.

The Risk of Acute Kidney Injury in Critically Ill Patients Receiving Concomitant Vancomycin With Piperacillin-Tazobactam or Cefepime.

PURPOSE: The objective of this study was to compare the incidence of acute kidney injury (AKI) among critically ill patients receiving combination therapy with vancomycin plus piperacillin-tazobactam (VPT) against patients receiving vancomycin plus cefepime (VC). METHODS: A retrospective cohort study of adult patients admitted to an intensive care unit between September 2012 and December 2016 was conducted. Patients were included if they received combination therapy with VPT or VC for ≥48 hours. Patients were excluded if creatinine clearance was <60 mL/min or received renal replacement therapy prior to the initiation of therapy. The primary end point was AKI, as defined by the Acute Kidney Injury Network classification, during or within 48 hours of completion of therapy. The incidence of AKI was compared between groups and multivariate analysis was performed to control for relevant confounders. RESULTS: A total of 394 patients received either VPT (n = 258) or VC (n = 136). There were no differences in baseline serum creatinine (0.8 [0.3]mg/dL vs 0.7 [0.3] mg/dL, P = 0.207), use of vasopressors (44% vs 38%, P = 0.255), mechanical ventilation (45% vs 40%, P = 0.350), or initial vancomycin trough (11.2 [5] mg/L vs 11 [4.8] mg/L, P = 0.668) between VPT and VC groups, respectively. The incidence of AKI was 28.7% for VPT patients versus 21.3% for VC patients (P = 0.114). Multivariate analysis revealed vancomycin trough >20 mg/L (odds ratio, OR [95% confidence interval, CI] = 2.69 [1.62-4.47]), baseline SCr (OR [95% CI] = 3.34 [1.43-7.80]), vasopressors (OR [95% CI] = 1.77 [1.04-3.04]), and duration of combination therapy (OR [95% CI] = 1.009 [1.003-1.015]) as independent risk factors for AKI. CONCLUSION: The risk of AKI was similar between VPT and VC groups in critically ill patients. Risk factors for AKI were related to baseline renal function, duration of combination therapy, supratherapeutic vancomycin troughs, and severity of illness.

Antibiotic Hypersensitivity Mechanisms.

Antibiotics are commonly prescribed to treat a variety of bacterial infections. As with all medications, hypersensitivity reactions may occur and clinicians should be able to recognize them accurately and recommend appropriate management. Antibiotic related hypersensitivity reactions may be one of four different types: Type I reactions, which are IgE mediated and may lead to anaphylaxis; Type II reactions that are antibody-mediated and may result in thrombocytopenia, neutropenia, or hemolytic anemia; Type III reaction that involves an immune complex formation such as vasculitis; and Type IV reactions that consist of four subtypes and typically include a rash of varying level of severity with or without systemic signs and symptoms. Herein, we describe the mechanisms of different types of allergic reactions to commonly prescribed antibiotics and offer recommendations for management. Further, we briefly refer to antibiotic reactions that mimic hypersensitivity reactions but are not immune mediated, such as pseudoallergies and serum sickness-like reactions.

Multicenter Study of Outcomes with Ceftazidime-Avibactam in Patients with Carbapenem-Resistant Enterobacteriaceae Infections.

Ceftazidime-avibactam is a novel cephalosporin-beta-lactamase inhibitor combination that is active against many carbapenem-resistant Enterobacteriaceae (CRE). We describe a retrospective chart review for 60 patients who received ceftazidime-avibactam for a CRE infection. In-hospital mortality was 32%, 53% of patients had microbiological cure, and 65% had clinical success. In this severely ill population with CRE infections, ceftazidime-avibactam was an appropriate option.

Risk Factors for 30-Day Mortality in Patients with Methicillin-Resistant Staphylococcus aureus Bloodstream Infections.

OBJECTIVES: Methicillin-resistant Staphylococcus aureus (MRSA) blood stream infections (BSI) are a major health care problem accounting for a large percentage of nosocomial infections. The aim of this study was to identify risk factors associated with 30-day mortality in patients with MRSA BSI. METHODS: This was a retrospective study performed in Southeast Michigan. Over a 9- year period, a total of 1,168 patients were identified with MRSA BSI. Patient demographics and clinical data were retrieved and evaluated using electronic medical health records. RESULTS: 30-day mortality during the 9-year study period was 16%. Significant risk factors for 30-day mortality were age, cancer, heart disease, neurologic disease, nursing home residence and Charlson score >3 with Odds Ratio (OR) of 1.03 (CI 1.02-1.04), 2.29 (CI 1.40-3.75), 1.78 (CI 1.20-2.63), 1.65 (CI 1.08-2.25), 1.66 (CI 1.02 - 2.70) and 1.86 (CI 1.18 - 2.95) correspondingly. Diabetes mellitus, peripheral vascular disease (PVD), and readmission were protective factors for 30-day mortality with OR of 0.53 (CI 0.36-0.78), 0.46 (CI 0.26-0.84) and 0.13 (CI0.05 - 0.32) respectively. CONCLUSIONS: Our study identified significant risk factors for 30-day mortality in patients with MRSA BSI. Interestingly, diabetes mellitus, PVD and readmission were protective effects on 30-day mortality. There was no statistically significant variability in 30-day mortality over the 9-year study period.

Ceftaroline fosamil monotherapy for methicillin-resistant Staphylococcus aureus bacteremia: a comparative clinical outcomes study.

OBJECTIVES: Vancomycin is the treatment of choice for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia; however, its use has been subject to scrutiny due to failure in severe infections. Ceftaroline fosamil (CPT-F) is approved for MRSA acute bacterial skin and skin structure infections, but not for bloodstream infections. The clinical outcomes of treatment with CPT-F in patients with MRSA bacteremia were evaluated. METHODS: Patients diagnosed with MRSA bacteremia at Henry Ford Hospital in Detroit, Michigan, USA, involving isolates with a vancomycin minimum inhibitory concentration ≥1.0mg/l and susceptible in vitro to CPT-F, were systematically reviewed retrospectively. Ceftaroline fosamil-treated patients were matched with at least two vancomycin- and/or one daptomycin-treated control patient based on age-patients age 65 years or greater or less than 65 years of age. Outcomes evaluated included the duration of hospitalization, duration of therapy, adverse events, relapse, hospital readmission, and death. RESULTS: Thirty consecutive cases of MRSA bacteremia treated with CPT-F during the period May 2011 to June 2013 were identified; these patients were matched to 56 MRSA bacteremia patients treated with vancomycin and 46 MRSA bacteremia patients treated with daptomycin. The primary source of MRSA bacteremia in the cohort treated with CPT-F was endocarditis (n=7, 23%), skin/wound (n=9, 30%), and bone/joint (n=8, 27%). The MRSA bacteremia in those treated with CPT-F was community-acquired in 43% of cases, healthcare-associated in 43%, and hospital-acquired in 13%. The mean length of hospital stay for these patients was 22 days. The overall 30-day mortality rate was 13% (n=4) in CPT-F patients versus 24% (n=11) in daptomycin patients and 11% (n=6) in vancomycin patients (p=0.188). CONCLUSIONS: CPT-F demonstrated comparable clinical outcomes in MRSA bacteremia patients compared with the other agents, especially as salvage therapy.

Emerging Issues and Treatment Strategies in Carbapenem-Resistant Enterobacteriaceae (CRE).

Carbapenems are the broadest spectrum antimicrobials utilized in the treatment of serious infections since the 1980s. Soon after their introduction, the discovery of carbapenem-resistant Enterobacteriaceae (CRE) was reported in the 1990s. Invasive CRE infections are associated with high mortality and limited treatment options making care for patients with these infections challenging for clinicians. Current practice has reverted back to the use of "older" antimicrobials, such as the polymyxins, tigecycline, and fosfomycin, to combat invasive CRE infections. However, recent approval of ceftazidime-avibactam has added another treatment option to the current antimicrobial armamentarium. Resistance among the "older" agents is still rare but has been reported. Currently, there are numerous agents that are under investigation as well as combination therapy that looks promising in the treatment of CRE infections.

Resistance to Non-glycopeptide Agents in Serious Staphylococcus aureus Infections.

The role of vancomycin in the treatment of serious Staphylococcus aureus infections, both methicillin-susceptible and methicillin-resistant, is becoming increasingly ineffective due to increasing MIC and failure. The development of reduced vancomycin susceptibility by S. aureus to glycopeptides highlights the need for clinicians to reexamine the roles of non-glycopeptide therapy. As the use of these alternative non-glycopeptides antimicrobials increases, it will become pertinent to monitor the rates of resistance. Large surveillance programs have provided data for resistance against S. aureus for the non-glycopeptides (daptomycin, ceftaroline, tigecycline, linezolid, and tedizolid). The current published literatures suggest that worldwide resistance rates to these non-glycopeptides for serious MRSA infections are still low. Implementation of antimicrobial stewardship programs will be crucial in prevention of resistance of these antimicrobials against S. aureus.

Pharmacokinetic and Pharmacodynamic Evaluation of Doripenem in Critically Ill Trauma Patients with Sepsis.

BACKGROUND: Doripenem is approved by the Food and Drug Administration for the treatment of patients with complicated intra-abdominal infections and complicated urinary tract infections. While studies have described the pharmacokinetics/pharmacodynamics (PK/PD) of doripenem in the critically ill, no study has described the probability of target attainment profile among trauma patients with sepsis. PATIENTS AND METHODS: This study was a prospective, open-label, pharmacokinetic study in the surgical intensive care unit (SICU) at Grady Health System. Thirty trauma patients with sepsis admitted to the SICU received doripenem 1 g infused over 4 hours every 8 hours for three doses. Blood samples were taken just before and after the third dose. A two-compartment model was fit to the data using non-parametric population PK modeling software. Embedded with the final PK model, a Monte Carlo Simulations (MCS) was performed to determine the PK/PD profile of doripenem 1 g, infused over 4 hours, every 8 hours after administration of the first and fourth doses. RESULTS: Overall, the model fit the data well, and mean (standard deviation) clearance and volume of the central compartment were 16.9 (11.4) L/h and 28.5 (16.0) L, respectively. In the MCS analyses, doripenem 1 g, infused over 4 hours, administered every 8 hours, conferred >90% probabilities of achieving 30-50% time greater than the minimum inhibitory concentration (30-50% T>MIC) for MICs ≤2 mg/L after infusion of both the first and fourth doses. The MCS indicated that more intensive doripenem dosing schemes should be considered for organisms with MIC values in excess of 2 mg/L. CONCLUSIONS: This is the first study to describe the doripenem PK/PD in critically ill patients with trauma. Among these patients, the MCS analyses suggest that current dosing strategies may be ineffective when the MIC value for the infecting pathogen is expected to be above 2 mg/L.

Neisseria gonorrhoeae and fosfomycin: Past, present and future.

Drug-resistant Neisseria gonorrhoeae has become a global health concern that requires immediate attention. Due to increasing resistance to cephalosporins, pursuing novel alternatives for treating N. gonorrhoeae infections is paramount. Whilst new drug development is often cumbersome, reviving antiquated antibiotic agents for treatment of modern infections has become prevalent in clinical practice. Fosfomycin exhibits bactericidal activity through a unique mechanism of action, and a variety of organisms including N. gonorrhoeae are susceptible. In vitro studies have demonstrated that fosfomycin can retain activity against ceftriaxone-resistant N. gonorrhoeae; however, it remains unclear whether there is synergy between fosfomycin and other antibiotics. Clinical investigations evaluating fosfomycin for the treatment of N. gonorrhoeae infections are confounded by methodological limitations, none the less they do provide some perspective on its potential role in therapy. Future studies are needed to establish a safe, convenient and effective fosfomycin regimen for treating N. gonorrhoeae infections.

Cleaning and disinfecting environmental surfaces in health care: Toward an integrated framework for infection and occupational illness prevention.

BACKGROUND: The Cleaning and Disinfecting in Healthcare Working Group of the National Institute for Occupational Safety and Health, National Occupational Research Agenda, is a collaboration of infection prevention and occupational health researchers and practitioners with the objective of providing a more integrated approach to effective environmental surface cleaning and disinfection (C&D) while protecting the respiratory health of health care personnel. METHODS: The Working Group, comprised of >40 members from 4 countries, reviewed current knowledge and identified knowledge gaps and future needs for research and practice. RESULTS: An integrated framework was developed to guide more comprehensive efforts to minimize harmful C&D exposures without reducing the effectiveness of infection prevention. Gaps in basic knowledge and practice that are barriers to an integrated approach were grouped in 2 broad areas related to the need for improved understanding of the (1) effectiveness of environmental surface C&D to reduce the incidence of infectious diseases and colonization in health care workers and patients and (2) adverse health impacts of C&D on health care workers and patients. Specific needs identified within each area relate to basic knowledge, improved selection and use of products and practices, effective hazard communication and training, and safer alternatives. CONCLUSION: A more integrated approach can support multidisciplinary teams with the capacity to maximize effective and safe C&D in health care.

Evaluation of in vitro susceptibility trends to vancomycin and daptomycin by strain type of Staphylococcus aureus causing bloodstream infections.

In total, 718 consecutive clinical meticillin-resistant Staphylococcus aureus (MRSA) isolates from 2006 to 2010 and 417 clinical meticillin-susceptible S. aureus (MSSA) isolates from mid-2007 to 2010 were evaluated. Isolates were from blood cultures obtained from separate patients in Detroit, MI, and were tested for in vitro susceptibility trends to vancomycin and daptomycin by molecular strain type. The MRSA pulsed-field gel electrophoresis (PFGE) results showed that 290 (40.4%) were USA100, 296 (41.2%) were USA300 and the remaining isolates were non-USA100/300. Vancomycin minimum inhibitory concentrations (MICs) by Etest [mean±standard deviation (S.D.) 1.55±0.26mg/L] in MRSA isolates showed no significant change over the 5-year period within all strain types, whilst daptomycin MICs by Etest (mean±S.D. 0.51±0.25mg/L) showed a significant downward trend across time (r=-0.243; P<0.001), with this trend occurring among all PFGE groups. For MSSA, a significant decrease in MICs to vancomycin was found by Etest (r=-0.160; P=0.001) and conversely a significant increase in daptomycin MICs by Etest was found (r=0.146; P=0.028). The results of this study showed that changes in MIC were not specific to strain molecular type. For vancomycin, there was no change in MRSA MICs and a decrease in MSSA MICs for blood isolates. For daptomycin, MICs decreased in MRSA and increased in MSSA blood isolates over the study period.

Characterization of heterogeneous vancomycin-intermediate resistance, MIC and accessory gene regulator (agr) dysfunction among clinical bloodstream isolates of staphyloccocus aureus.

BACKGROUND: The development of hVISA has been associated with vancomycin clinical failures and is commonly misidentified in clinical microbiology laboratories. Therefore, the objectives of this present study was to improve the reliability of methodologies and criteria for identifying hVISA, evaluate the prevalence of hVISA among clinical bloodstream isolates of S. aureus and determine if there exists a relationship between accessory gene regulator (agr) dysfunction and the hVISA phenotype. METHODS: The presence of hVISA in 220 clinical S. aureus isolates (121 MSSA, 99 MRSA) from bloodstream infections was examined by CLSI broth microdilution, Macro & Standard Etest. Isolates which were classified as hVISA by Macro Etest, were additionally evaluated using a modified PAP-AUC method using a modified starting inoculum of 10(10) CFU/mL, and growth on brain heart infusion agar with 4 mg/L vancomycin (BHIV4) at 10(8) and 10(10) CFU/mL, and agr function was assessed by delta-hemolysin production. RESULTS: Broth microdilution MIC(50/90) of S.aureus and hVISA was 1.0/2.0 and 1.5/2.0 mg/L (p= 0.02), respectively. Macro Etest identified 12 (5.5%) hVISA isolates; higher among MRSA (9.1%) versus MSSA (2.5%) (p = 0.03). The mean modified PAP-AUC ratios (> 0.8) of 7 MRSA strains and 3 MSSA strains were significantly different (p = 0.001). 58% of hVISA strains were found to be agr dysfunctional when 21% of MRSA strains were agr dysfunctional. hVISA was detected among S. aureus bloodstream isolates, which were classified as susceptible among clinical microbiology laboratories. CONCLUSIONS: Evaluating the correlation between Etest MICs and modified PAP-AUC ratio values will add further improvement of discriminating hVISA, and agr dysfunction may be predictive of strains which display a greater predilection to display the hVISA phenotype.