Early Response Assessment to Guide Management of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections With Vancomycin Therapy

Background

A subset of vancomycin-treated patients with methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) developed persistent positive blood cultures. Treatment eventually failed.

Methods

A retrospective study was conducted to determine whether early response on day 3 after initiation of vancomycin therapy for MRSA BSI was associated with reduced rates of persistent bacteremia, end-of-treatment failure, and infection-related mortality. Patients’ medical charts were reviewed. Susceptibility testing and molecular characterization of bacterial isolates were performed.

Results

In this elderly cohort (n = 111; median age 70 years, interquartile range: 57–80 years), early response was observed in 62% of patients and was significantly (P < 0.0001) associated with lower rates of end-of-treatment failure (19% vs 57%) and infection-related death (1% vs 29%), but not with persistent bacteremia (17% vs 29%, P = 0.23). Nearly half (46%; 46 of 100 patients) remained on vancomycin therapy for the entire treatment course; those who continued despite lack of early response had a trend toward a higher risk of death than those who were switched to alternative therapy (38% vs 10%, P = NS). Most (68%) isolates had vancomycin MIC of >1 µg/mL, whereas 10% showed heterogeneous glycopeptide-intermediate Staph aureus (hGISA) phenotype. Nearly half (47%) were typed with staphylococcal cassette chromosome mec IV or V. In a multivariate logistic regression model, lack of response at day 3 was the strongest predictor for end-of-treatment failure, after adjustment for confounders such as age, Acute Physiology And Chronic Health Evaluation II score, intensive care unit admission, vancomycin MIC >1 µg/mL, unbound trough concentration <4 to 5× MIC, and continued vancomycin therapy without change.

Conclusions

Early response assessment after initiation of vancomycin therapy appeared to be useful for considering further diagnostic workup or a switch to alternative therapy to affect a positive outcome in patients with MRSA BSI.     

耐甲氧西林金黄色葡萄球菌血流感染：关注感染来源和去路

耐甲氧西林金黄色葡萄球菌（MRSA）血流感染发病率和病死率居高不下。规范留取血标本后血培养阳性是诊断菌血症的金标准。临床诊断MRSA血流感染后应注意寻找可能的原发感染源和迁徙感染灶，及时处理原发感染灶和转移性感染灶是MRSA血流感染治疗成功的前提与基础。指南推荐万古霉素和达托霉素是治疗MRSA血流感染的一线抗生素，而利奈唑胺可作为万古霉素耐药或合并肾功能不全MRSA血流感染患者补救性治疗。系统回顾MRSA血流感染若干热点问题，关注感染来源和去路，具有重要临床意义。     

Clinical Outcomes in Patients with Heterogeneous Vancomycin-Intermediate Staphylococcus aureus Bloodstream Infection

The prevalence of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) infections varies in the literature, a problem complicated by the lack of routine screening procedures; however, limited data suggest that hVISA has been associated with persistent bloodstream infections (BSI) and vancomycin failure, yet these studies have been confounded by design issues. We conducted this study to compare the characteristics of patients with BSI caused by hVISA with those with vancomycin-susceptible Staphylococcus aureus (VSSA) treated with vancomycin. This retrospective, multicenter matched (1:1) cohort study compared the clinical characteristics and outcomes of hVISA and VSSA. Patients with hVISA methicillin-resistant Staphylococcus aureus (MRSA) BSI from 2004 to 2012 were matched to VSSA-MRSA BSI patients. The primary outcome was failure of vancomycin treatment, defined as a composite of persistent bacteremia (≥7 days), persistent signs and symptoms, change of MRSA antibiotic, recurrent BSI, or MRSA-related mortality. We identified 122 matched cases. The overall vancomycin failure rate was 57% (82% hVISA versus 33% VSSA; P < 0.001). The individual components of failure in hVISA versus VSSA were persistent bacteremia, 59% versus 21% (P < 0.001); change in MRSA therapy, 54% versus 25% (P = 0.001); MRSA-related mortality, 21% versus 10% (P = 0.081); and recurrence of BSI, 26% versus 2% (P < 0.001). Using logistic regression analysis and adjusting for covariates, hVISA (adjusted odds ratio [aOR], 11.1; 95% confidence interval [CI], 4.3 to 28.7) and intensive care unit (ICU) admission (aOR, 4.5; 95% CI, 1.8 to 11.6) were still independently associated with vancomycin failure. Relative to VSSA BSI, patients with hVISA were more likely to experience failure of vancomycin treatment, including persistent bacteremia and recurrence. Our results indicate that hVISA was responsible for considerable morbidity.     

血液感染金黄色葡萄球菌耐药性及甲氧西林耐药株危险因素分析

目的分析血液感染金黄色葡萄球菌耐药性及甲氧西林耐药株感染的危险因素。方法对本院2009~2011年金黄色葡萄球菌血液感染患者流行病学资料进行回顾性研究。将感染患者分为甲氧西林敏感(MSSA)组和耐药组(MRSA),然后采用1∶2成组病例对照方法选取同时期非金黄色葡萄球菌感染患者作为对照组,对MRSA血液感染危险因素进行分析。结果血液标本分离的289株金黄色葡萄球菌中192株为甲氧西林耐药株,占66.90%,MRSA组耐药性明显高于MSSA组。甲氧西林耐药组和敏感组感染患者的病死率均高于对照组,但是MRSA组与MSSA组病死率比较差异无统计学意义。Logistic回归分析显示,重症监护室(ICU)入住(>7d)、中心静脉置管、联合用药大于2种和抗生素使用时间大于2周是MRSA感染的独立危险因素。结论血液分离金黄色葡萄球菌MRSA株检出率高、耐药性强,患者的病死率高。MRSA血液感染具有多个独立危险因素,加强对这些独立危险因素的控制可有效预防其感染扩散。     

Daily practice and prognostic factors for pneumonia caused by methicillin-resistant Staphylococcus aureus in Japan: A multicenter prospective observational cohort study

Pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA) is associated with poor clinical outcomes. We surveyed clinical outcomes of MRSA pneumonia in daily practice to identify risk factors for the clinical failure and mortality in patients with MRSA pneumonia.This multicenter prospective observational study was performed across 48 Japanese medical institutions. Adult patients with culture-positive MRSA pneumonia were recruited and treated with anti-MRSA antibiotics. The relationships between clinical and microbiological characteristics and clinical outcomes at test of cure (TOC) or 30-day all-cause mortality were analyzed.In total, 199 eligible patients, including nursing and healthcare-associated pneumonia (n = 95), hospital-acquired pneumonia (n = 76), and community-acquired pneumonia (n = 25), received initial treatment with anti-MRSA agents such as vancomycin (n = 135), linezolid (n = 36), or teicoplanin (n = 22). Overall clinical failure rate at TOC and the 30-day mortality rate were 51.1% (48/94 patients) and 33.7% (66/196 patients), respectively. Multivariable logistic regression analyses for vancomycin-treated populations revealed that abnormal white blood cell count (odds ratio [OR] 4.34, 95% confidence interval [CI] 1.31–14.39) was a risk factor for clinical failure and that no therapeutic drug monitoring (OR 3.10, 95% CI 1.35–7.12) and abnormally high C-reactive protein level (OR 3.54, 95% CI 1.26–9.92) were risk factors for mortality.In conclusion, this study provides evidence that majority of MRSA pneumonia patients are initially treated with vancomycin in Japan, and the absence of therapeutic drug monitoring for vancomycin is significantly associated with the mortality in patients with MRSA pneumonia.     

Relationship between vancomycin MIC and failure among patients with methicillin-resistant Staphylococcus aureus bacteremia treated with vancomycin

There is growing concern that vancomycin has diminished activity for methicillin-resistant Staphylococcus aureus (MRSA) infections, with vancomycin MICs at the high end of the CLSI susceptibility range. Despite this growing concern, there are limited clinical data to support this notion. To better elucidate this, a retrospective cohort study was conducted among patients with MRSA bloodstream infections who were treated with vancomycin between January 2005 and May 2007. The inclusion criteria were as follows: at least 18 years old, nonneutropenic, with an MRSA culture that met the CDC criteria for bloodstream infection, had received vancomycin therapy within 48 h of the index blood culture, and survived >24 h after vancomycin administration. Failure was defined as 30-day mortality, bacteremia ≥10 days on vancomycin therapy, or a recurrence of MRSA bacteremia within 60 days of vancomycin discontinuation. Classification and regression tree (CART) analysis identified the vancomycin MIC breakpoint associated with an increased probability of failure. During the study period, 92 patients met the inclusion criteria. The vancomycin MIC breakpoint derived by CART analysis was ≥1.5 mg/liter. The 66 patients with vancomycin MICs of ≥1.5 mg/liter had a 2.4-fold increase in failure compared to patients with MICs of ≤1.0 mg/liter (36.4% and 15.4%, respectively; P = 0.049). In the Poisson regression, a vancomycin MIC of ≥1.5 mg/liter was independently associated with failure (adjusted risk ratio, 2.6; 95% confidence interval, 1.3 to 5.4; P = 0.01). These data strongly suggest that patients with MRSA bloodstream infections with vancomycin MICs of ≥1.5 mg/liter respond poorly to vancomycin. Alternative anti-MRSA therapies should be considered for these patients.     

Higher clinical success in patients with ventilator-associated pneumonia due to methicillin-resistant Staphylococcus aureus treated with linezolid compared with vancomycin: results from the IMPACT-HAP study

Introduction

Controversy exists regarding optimal treatment for ventilator-associated pneumonia (VAP) due to methicillin-resistant Staphylococcus aureus (MRSA). The primary objective of this study was to compare clinical success of linezolid versus vancomycin for the treatment of patients with MRSA VAP.

Methods

This was a multicenter, retrospective, observational study of patients with VAP (defined according to Centers for Disease Control and Prevention criteria) due to MRSA who were treated with linezolid or vancomycin. MRSA VAP was considered when MRSA was isolated from a tracheal aspirate or bronchoalveolar lavage. Clinical success was evaluated by assessing improvement or resolution of signs and symptoms of VAP by day 14. After matching on confounding factors, logistic regression models were used to determine if an association existed between treatment arm and clinical success.

Results

A total of 188 patients were evaluated (101 treated with linezolid and 87 with vancomycin). The mean ± standard deviation Acute Physiology and Chronic Health Evaluation (APACHE) II score was 21 ± 11 for linezolid- and 19 ± 9 for vancomycin-treated patients (P = 0.041). Clinical success occurred in 85% of linezolid-treated patients compared with 69% of vancomycin-treated patients (P = 0.009). After adjusting for confounding factors, linezolid-treated patients were 24% more likely to experience clinical success than vancomycin-treated patients (P = 0.018).

Conclusions

This study adds to the evidence indicating that patients with MRSA VAP who are treated with linezolid are more likely to respond favorably compared with patients treated with vancomycin.     

Vancomycin AUC24/MIC ratio in patients with complicated bacteremia and infective endocarditis due to methicillin-resistant Staphylococcus aureus and its association with attributable mortality during hospitalization

Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of complicated bacteremia (CB) and infective endocarditis (IE). The gold standard treatment for these infections is vancomycin. A vancomycin area under the concentration-time curve from 0 to 24 h (AUC(24))/MIC ratio of >400 has been suggested as a target to achieve clinical effectiveness, and yet to date no study has quantitatively investigated the AUC(24)/MIC ratio and its association with attributable mortality (AM). We performed a review of patients treated for MRSA CB and IE from 1 July 2006 to 30 June 2008. AM was defined as deaths where CB or IE was documented as the main cause or was mentioned as the main diagnosis. Classification and regression tree analysis (CART) was used to identify the AUC(24)/MIC ratio associated with AM. Mann-Whitney and Fisher exact tests were used for univariate analysis, and logistic regression was used for multivariate modeling. The MICs were determined by Etest, and the AUC(24) was determined using a maximum a posteriori probability-Bayesian estimator. A total of 32 CB and 18 IE patients were enrolled. The overall crude mortality and AM were 24 and 16%, respectively. The CART-derived partition for the AUC(24)/MIC ratio and AM was <211. Patients with an AUC(24)/MIC ratio of <211 had a >4-fold increase in AM than patients who received vancomycin doses that achieved an AUC(24)/MIC ratio of ≥211 (38 and 8%, respectively; P = 0.02). In bivariate analysis the APACHE-II score and an AUC(24)/MIC ratio of <211 were significantly associated with AM. In the multivariate model, the APACHE-II score (odds ratio, 1.24; P = 0.04) and a vancomycin AUC/MIC ratio of <211 (odds ratio, 10.4; P = 0.01) were independent predictors of AM. In our analysis, independent predictors of AM were the APACHE-II score and an AUC(24)/MIC ratio of <211. We believe further investigations are warranted.     

High prevalence of isolates with reduced glycopeptide susceptibility in persistent or recurrent bloodstream infections due to methicillin-resistant Staphylococcus aureus

Reduced susceptibility to glycopeptides in methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates is considered a risk factor for failure of glycopeptide therapy. We compared the prevalences of MRSA isolates with reduced glycopeptide susceptibility in patients with versus without persistent or recurrent MRSA bloodstream infections. A retrospective cohort study at the University Hospital of Geneva identified 27 patients with persistent or recurrent clonally related MRSA bacteremic episodes over an 8-year period, which included 208 consecutive nosocomial MRSA bacteremic episodes. Vancomycin and teicoplanin MICs were determined by a modified macrodilution assay allowing improved detection of glycopeptide-intermediate MRSA isolates (GISA), characterized by elevated teicoplanin or/and vancomycin MICs (≥ 4 μg/ml). For 16 patients (59%), their pretherapy and/or posttherapy MRSA isolates showed elevated teicoplanin MICs, among which 10 (37%) concomitantly displayed elevated vancomycin MICs. In contrast, 11 other patients (41%) were persistently or recurrently infected with non-GISA isolates. In comparison, only 39 (22%) of 181 single isolates from patients with no microbiological evidence of persistent or recurrent infections showed elevated teicoplanin MICs, among which 14 (8%) concomitantly displayed elevated vancomycin MICs. Clinical, microbiological, and pharmacokinetic variables for patients persistently or recurrently infected with GISA or non-GISA isolates were similar. Bacteremic patients with a poor response to glycopeptide therapy had a 2.8-fold- and 4.8-fold-higher rates of MRSA isolates displaying elevated teicoplanin and vancomycin MICs, respectively, than patients with single isolates (P < 0.0001). Detection of elevated teicoplanin MICs may help to predict a poor response to glycopeptide therapy in MRSA bacteremic patients.     

Predictors of mortality in multidrug-resistant Klebsiella pneumoniae bloodstream infections

The dramatic increase of antibiotic resistance in Klebsiella pneumoniae has been associated with fatal outcomes. First, bloodstream infections (BSIs) caused by extended-spectrum β-lactamases (ESBL) Enterobacteriaceae have been associated with treatment failure, more recently BSIs caused by carbapenem-resistant K. pneumoniae (CR-KP) have been reported to be fatal in approximately 50% of cases. Severity of underlying disease, intensive care unit stay at infection onset, infection with ESBL or CR-KP strain and delay in administration of appropriate therapy are among the most common risk factors for mortality in patients with K. pneumoniae BSI, while infection source control and early appropriate antimicrobial treatment have been associated with survival. Thus, risk assessment for ESBL and/or CR-KP is mandatory in patients with suspicion of K. pneumoniae BSI. Here, we examine current evidence regarding risk factors for mortality in patients with K. pneumoniae BSI and address the issue of a risk prediction model for CR-KP BSI.     

Results of a double-blind, randomized trial of ceftobiprole treatment of complicated skin and skin structure infections caused by gram-positive bacteria

Ceftobiprole is the first broad-spectrum cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA) to be assessed in late-stage clinical trials. As a pivotal step in the clinical development of ceftobiprole, a multicenter, global, randomized, double-blind trial was conducted to compare the efficacy of ceftobiprole to that of vancomycin in patients with complicated skin and skin structure infections (cSSSIs) caused by gram-positive bacteria. The primary objective was to assess noninferiority on the basis of the cure rates 7 to 14 days after the completion of therapy in patients administered ceftobiprole 500 mg every 12 h or vancomycin 1 g every 12 h. Of 784 patients randomized, 282 receiving ceftobiprole and 277 receiving vancomycin were clinically evaluable. Of these patients, 93.3% treated with ceftobiprole and 93.5% treated with vancomycin were cured (95% confidence interval of difference, -4.4%, 3.9%). The cure rates for patients with MRSA infections were 91.8% (56/61) with ceftobiprole treatment and 90.0% (54/60) with vancomycin treatment (95% confidence interval of difference, -8.4%, 12.1%). At least one adverse event (AE) was reported by 52% of the ceftobiprole-treated patients and 51% of the vancomycin-treated patients. The most common AEs reported by the ceftobiprole-treated patients were nausea (14%) and taste disturbance (8%). Discontinuation of the study drug because of treatment-emergent AEs occurred in 4% (n = 17) of the ceftobiprole-treated patients and 6% (n = 22) of the vancomycin-treated patients. The results of this trial support the use of ceftobiprole as an effective and well-tolerated treatment option for patients with cSSSIs caused by a spectrum of gram-positive bacteria.     

Clinical impact of antimicrobial resistance in European hospitals: excess mortality and length of hospital stay related to methicillin-resistant Staphylococcus aureus bloodstream infections

Antimicrobial resistance is threatening the successful management of nosocomial infections worldwide. Despite the therapeutic limitations imposed by methicillin-resistant Staphylococcus aureus (MRSA), its clinical impact is still debated. The objective of this study was to estimate the excess mortality and length of hospital stay (LOS) associated with MRSA bloodstream infections (BSI) in European hospitals. Between July 2007 and June 2008, a multicenter, prospective, parallel matched-cohort study was carried out in 13 tertiary care hospitals in as many European countries. Cohort I consisted of patients with MRSA BSI and cohort II of patients with methicillin-susceptible S. aureus (MSSA) BSI. The patients in both cohorts were matched for LOS prior to the onset of BSI with patients free of the respective BSI. Cohort I consisted of 248 MRSA patients and 453 controls and cohort II of 618 MSSA patients and 1,170 controls. Compared to the controls, MRSA patients had higher 30-day mortality (adjusted odds ratio [aOR] = 4.4) and higher hospital mortality (adjusted hazard ratio [aHR] = 3.5). Their excess LOS was 9.2 days. MSSA patients also had higher 30-day (aOR = 2.4) and hospital (aHR = 3.1) mortality and an excess LOS of 8.6 days. When the outcomes from the two cohorts were compared, an effect attributable to methicillin resistance was found for 30-day mortality (OR = 1.8; P = 0.04), but not for hospital mortality (HR = 1.1; P = 0.63) or LOS (difference = 0.6 days; P = 0.96). Irrespective of methicillin susceptibility, S. aureus BSI has a significant impact on morbidity and mortality. In addition, MRSA BSI leads to a fatal outcome more frequently than MSSA BSI. Infection control efforts in hospitals should aim to contain infections caused by both resistant and susceptible S. aureus.     

耐甲氧西林金黄色葡萄球菌血流感染死亡患者临床特征及危险因素分析

目的 分析耐甲氧西林金黄色葡萄球菌(MRSA)血流感染患者临床特征及预后危险因素,为控制和预防MRSA血流感染提供依据.方法 回顾性分析2015年1月—2020年12月南京医科大学第一附属医院门诊及住院血液培养MRSA阳性患者临床特征和预后危险因素.结果 142例MRSA血流感染患者以男性、老年为主,生存99例,死亡4...     

造血干细胞移植后血流感染的临床分析

目的:分析造血干细胞移植(HSCT)患者血流感染的临床特征。方法:回顾性分析2013年1月至2020年6月在我科行HSCT的910例患者的临床特征、发生血流感染的病原菌分布及药敏情况。结果:910例患者中,111例在移植后100 d内确诊血流感染,98例的血流感染发生在粒细胞缺乏(粒缺)期。多因素分析显示,预处理方案含抗胸腺细胞球蛋白(ATG)、粒缺持续时间长、单个核细胞(MNC)输注量低是HSCT后血流感染的独立危险因素。分离出的121株病原菌中,革兰氏阴性(G-)菌76株(62.8%),革兰氏阳性(G+)菌40株(33.1%),真菌5株(4.1%)。病原菌前3位依次为大肠埃希菌、表皮葡萄球菌和铜绿假单胞菌。大肠埃希菌、肺炎克雷伯菌和铜绿假单胞菌对碳青霉烯类药物耐药率分别为14.3%、7.7%和66.7%。G+菌对万古霉素、利奈唑胺、替考拉宁的敏感率分别为97.5%、100%和100%。血流感染患者HSCT后100 d死亡率显著高于无血流感染患者(P<0.001)。结论:预处理方案含ATG、粒缺持续时间长、MNC输注量低是HSCT后血流感染的独立危险因素,移植后血流感染病原菌以...     

Stratification of the Impact of Inappropriate Empirical Antimicrobial Therapy for Gram-Negative Bloodstream Infections by Predicted Prognosis

The bloodstream infection mortality risk score (BSIMRS) predicts the outcome of patients with Gram-negative bloodstream infections (BSI) with high discrimination. This retrospective cohort study examined the impact of inappropriate antimicrobial therapy on mortality in adult patients with Gram-negative BSI admitted to Palmetto Health Hospitals in Columbia, SC, USA, from 1 January 2011 to 31 December 2012 after stratification by predicted prognosis at initial presentation using BSIMRS. A multivariate Cox regression model was used to identify independent risk factors for 28-day mortality overall and within each predefined BSIMRS category (<5, 5 to 9, and ≥10). Relative risk reduction (RRR), absolute risk reduction (ARR), and number needed to treat (NNT) were calculated from a predictive logistic regression model of mortality. Overall, 390 unique patients with first episodes of Gram-negative BSI were identified. The median age was 66 years, and 229 (59%) were women. There was significant association between inappropriate antimicrobial therapy and mortality in patients with BSIMRS of 5 to 9 (adjusted hazard ratio [aHR], 3.55; 95% confidence intervals [CI], 1.22 to 8.31; P = 0.02) and BSIMRS of ≥10 (aHR, 4.99; 95% CI, 1.09 to 22.87; P = 0.04) but not in those with BSIMRS of <5 (aHR, 3.34; 95% CI, 0.17 to 22.77; P = 0.34). RRR, ARR, and NNT were 0.25, 0.02, and 63 for BSIMRS of <5; 0.56, 0.32, and 3 for BSIMRS of 5 to 9; and 0.39, 0.39, and 3 for BSIMRS of ≥10, respectively. There is a significant benefit from appropriate antimicrobial therapy in patients with Gram-negative BSI with guarded (BSIMRS of 5 to 9) and poor (BSIMRS of ≥10) predicted prognosis. Survival difference remains unclear among those with good predicted prognosis (BSIMRS of <5) at initial presentation.     

Health Economic Evaluation of Patients Treated for Nosocomial Pneumonia Caused by Methicillin-resistant Staphylococcus aureus: Secondary Analysis of a Multicenter Randomized Clinical Trial of Vancomycin and Linezolid

Purpose

Results from studies comparing health care resource use (HCRU), costs of treatment, and cost-effectiveness of linezolid compared with vancomycin therapy in the treatment of hospitalized patients with methicillin-resistant Staphylococcus aureus (MRSA) nosocomial pneumonia are limited in the published literature. We therefore conducted an analysis to compare the HCRU, costs of treatment, and cost-effectiveness of linezolid compared with vancomycin in the treatment of hospitalized patients with MRSA nosocomial pneumonia using data from a Phase IV clinical trial. The economic effect of moderate to severe adverse events (MSAEs) and the development of renal failure were also evaluated.

Methods

We performed a post hoc analysis of data from a Phase IV, double-blind, randomized, comparator-controlled, multicenter trial that compared linezolid and vancomycin treatment in patients with MRSA nosocomial pneumonia. HCRU and costs were compared based on treatment, development of MSAEs, and development of renal failure using data from the modified intent-to-treat population. Predictors of costs were evaluated using generalized linear models. A piggyback cost-effectiveness analysis was conducted to assess the incremental cost-effectiveness ratio of linezolid versus vancomycin, given the significantly higher clinical success of linezolid compared with vancomycin found in the trial.

Findings

Overall, HCRU and costs were similar between the linezolid and vancomycin treatment groups; drug costs were significantly higher and dialysis costs significantly lower for linezolid- compared with vancomycin-treated patients. Total treatment costs were approximately $8000 higher (P = .046) for patients who developed renal failure compared with those who did not. Renal failure occurred more commonly in patients randomized to receive vancomycin (15%) compared with linezolid (4%; P < .001). Region, ventilator-associated pneumonia, clinical failure, and development of renal failure were associated with significantly higher total costs. The point estimate incremental cost-effectiveness ratio for linezolid compared with vancomycin was $16,516 per treatment success, with linezolid dominant in 24% and dominated in <2% of bootstrapped samples.

Implications

This phase 4 clinical trial conducted in patients with MRSA-confirmed nosocomial pneumonia reveals that linezolid- compared with vancomycin-treated patients had similar HCRU and total overall costs. Fewer patients developed renal failure during the study while taking linezolid compared with vancomycin, and patients with a documented MSAE or renal failure had increased HCRU and costs. In summary, linezolid may be a cost-effective treatment strategy in MRSA-confirmed nosocomial pneumonia.     

Impact of Reduced Vancomycin MIC on Clinical Outcomes of Methicillin-Resistant Staphylococcus aureus Bacteremia

Vancomycin has been a key antibiotic agent for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. However, little is known about the relationship between vancomycin MIC values at the higher end of the susceptibility range and clinical outcomes. The aim of this study was to determine the impact of MRSA bacteremia on clinical outcomes in patients with a vancomycin MIC near the upper limit of the susceptible range. Patients with MRSA bacteremia were divided into a high-vancomycin-MIC group (2 μg/ml) and a low-vancomycin-MIC group (≤1.0 μg/ml). We examined the relationship between MIC, genotype, primary source of bacteremia, and mortality. Ninety-four patients with MRSA bacteremia, including 31 with a high vancomycin MIC and 63 with a low MIC were analyzed. There was no significant difference between the presence of agr dysfunction and SCCmec type between the two groups. A higher vancomycin MIC was not found to be associated with mortality. In contrast, high-risk bloodstream infection sources (hazard ratio [HR], 4.63; 95% confidence interval [CI] = 1.24 to 17.33) and bacterial eradication after treatment (HR, 0.06; 95% CI = 0.02 to 0.17), irrespective of vancomycin MIC, were predictors of all-cause 30-day mortality. Our study suggests that a high-risk source of bacteremia is likely to be associated with unfavorable clinical outcomes, but a high vancomycin MIC in a susceptible range, as well as genotype characteristics, are not associated with mortality.     

Effects of prolonged vancomycin administration on methicillin-resistant Staphylococcus aureus (MRSA) in a patient with recurrent bacteraemia

OBJECTIVES: To evaluate microbiological properties of methicillin-resistant Staphylococcus aureus (MRSA) during prolonged vancomycin therapy. METHODS: We evaluated vancomycin susceptibility and heteroresistance, accessory gene regulator (agr) function, autolysis, biofilm production and in vitro vancomycin killing in serial MRSA bloodstream isolates obtained over a 30 month period from a patient with a chronic endovascular infection. RESULTS: Despite the fact that the MRSA in this patient had the same genetic background as other clinical glycopeptide intermediate-resistant S. aureus (GISA) isolates, vancomycin administered for 9 months, maintaining serum concentrations >10 mg/L, did not select for GISA. Minimal changes in vancomycin susceptibility were detected using agar dilution and population analysis methods. We noted increases in delta haemolysin production, autolysis and the bactericidal effects of vancomycin in vitro against the MRSA obtained after prolonged vancomycin suppressive therapy was discontinued. CONCLUSIONS: Despite the lack of development of detectable resistance, MRSA exposed to vancomycin for prolonged periods may begin to develop vancomycin tolerance and decreased autolysis. In addition, suppression of agr function appears to end after vancomycin is stopped. Whether these changes are prerequisites for attenuated vancomycin efficacy and the development of glycopeptide resistance warrants further study. The development of vancomycin resistance may be more difficult under conditions where vancomycin serum concentrations are maintained >10 mg/L.     

Efficacy of Linezolid in Treatment of Experimental Endocarditis Caused by Methicillin-Resistant Staphylococcus aureus

The efficacies of orally (p.o.) dosed linezolid and intravenously (i.v.) dosed vancomycin against methicillin-resistant Staphylococcus aureus (MRSA) in rabbits with experimental aortic-valve endocarditis were investigated. After endocarditis was established with a recent clinical MRSA isolate, rabbits were dosed for 5 days with linezolid (p.o., three times a day) at either 25, 50, or 75 mg/kg of body weight or vancomycin (i.v., twice a day) at 25 mg/kg. The 25-mg/kg linezolid group had a high mortality rate and bacterial counts in the valve vegetations that were not different from those of the controls. Linezolid dosed p.o. at 50 and 75 mg/kg and i.v. vancomycin produced statistically significant reductions in bacterial counts compared to those of the untreated controls. The reduced bacterial counts and culture-negative valve rates for the animals treated with linezolid at 75 mg/kg were similar to those for the vancomycin-treated animals. Concentrations of linezolid in plasma were determined at several points in the dosing regimen. These results suggest that the efficacy of linezolid in this infection model is related to trough levels in plasma that remain above the MIC for this microorganism. At the ineffective dose of linezolid (25 mg/kg) the concentration at sacrifice was 0.045 times the MIC, whereas the concentrations of linezolid in plasma in the 50- and 75-mg/kg groups were 2 and 5 times the MIC at sacrifice, respectively. The results from this experimental model suggest that the oxazolidinone linezolid may be effective for the treatment of serious staphylococcal infections when resistance to other antimicrobials is present.     

Acquired bloodstream infection in the intensive care unit: incidence and attributable mortality

Introduction

To estimate the incidence of intensive care unit (ICU)-acquired bloodstream infection (BSI) and its independent effect on hospital mortality.

Methods

We retrospectively studied acquisition of BSI during admissions of >72 hours to adult ICUs from two university-affiliated hospitals. We obtained demographics, illness severity and co-morbidity data from ICU databases and microbiological diagnoses from departmental electronic records. We assessed survival at hospital discharge or at 90 days if still hospitalized.

Results

We identified 6339 ICU admissions, 330 of which were complicated by BSI (5.2%). Median time to first positive culture was 7 days (IQR 5-12). Overall mortality was 23.5%, 41.2% in patients with BSI and 22.5% in those without. Patients who developed BSI had higher illness severity at ICU admission (median APACHE III score: 79 vs. 68, P < 0.001). After controlling for illness severity and baseline demographics by Cox proportional-hazard model, BSI remained independently associated with risk of death (hazard ratio from diagnosis 2.89; 95% confidence interval 2.41-3.46; P < 0.001). However, only 5% of the deaths in this model could be attributed to acquired-BSI, equivalent to an absolute decrease in survival of 1% of the total population. When analyzed by microbiological classification, Candida, Staphylococcus aureus and gram-negative bacilli infections were independently associated with increased risk of death. In a sub-group analysis intravascular catheter associated BSI remained associated with significant risk of death (hazard ratio 2.64; 95% confidence interval 1.44-4.83; P = 0.002).

Conclusions

ICU-acquired BSI is associated with greater in-hospital mortality, but complicates only 5% of ICU admissions and its absolute effect on population mortality is limited. These findings have implications for the design and interpretation of clinical trials.