Antimicrobial Stewardship in the Emergency Department Observation Unit: Definition of a New Indicator and Evaluation of Antimicrobial Use and Clinical Outcomes.

We aimed to define a novel indicator for monitoring antimicrobial use specifically in the Emergency Department Observation Unit (EDOU) and to assess the long-term impact of an institutional education-based antimicrobial stewardship program (ASP) on the antimicrobial prescribing pattern and clinical outcomes in this setting. A quasi-experimental interrupted time-series study was performed from 2011 to 2022. An educational ASP was implemented at the EDOU in 2015. To estimate changes in antimicrobial use, we designed an indicator adjusted for patients at risk of antimicrobial prescribing: defined daily doses (DDDs) per 100 patients transferred from the Emergency Department to the Observation Unit (TOs) per quarter. The number of bloodstream infections (BSIs) and the crude all-cause 14-day mortality were assessed as clinical outcomes. Antimicrobial use showed a sustained reduction with a trend change of -1.17 DDD per 100 TO and a relative effect of -45.6% (CI95% -64.5 to -26.7), particularly relevant for meropenem and piperacillin-tazobactam, with relative effects of -80.4% (-115.0 to -45.7) and -67.9% (-93.9 to -41.9), respectively. The incidence density of all BSIs increased significantly during the ASP period, with a relative effect of 123.2% (41.3 to 284.7). The mortality rate remained low and stable throughout the study period, with an absolute effect of -0.7% (-16.0 to 14.7). The regular monitoring of antimicrobial use in the EDOU by using this new quantitative indicator was useful to demonstrate that an institutional education-based ASP successfully achieved a long-term reduction in overall antimicrobial use, with a low and steady BSI mortality rate.

Rates and Predictors of Treatment Failure in Staphylococcus aureus Prosthetic Joint Infections According to Different Management Strategies: A Multinational Cohort Study-The ARTHR-IS Study Group.

INTRODUCTION: Guidelines have improved the management of prosthetic joint infections (PJI). However, it is necessary to reassess the incidence and risk factors for treatment failure (TF) of Staphylococcus aureus PJI (SA-PJI) including functional loss, which has so far been neglected as an outcome. METHODS: A retrospective cohort study of SA-PJI was performed in 19 European hospitals between 2014 and 2016. The outcome variable was TF, including related mortality, clinical failure and functional loss both after the initial surgical procedure and after all procedures at 18 months. Predictors of TF were identified by logistic regression. Landmark analysis was used to avoid immortal time bias with rifampicin when debridement, antibiotics and implant retention (DAIR) was performed. RESULTS: One hundred twenty cases of SA-PJI were included. TF rates after the first and all surgical procedures performed were 32.8% and 24.2%, respectively. After all procedures, functional loss was 6.0% for DAIR and 17.2% for prosthesis removal. Variables independently associated with TF for the first procedure were Charlson ≥ 2, haemoglobin < 10 g/dL, bacteraemia, polymicrobial infection and additional debridement(s). For DAIR, TF was also associated with a body mass index (BMI) > 30 kg/m2 and delay of DAIR, while rifampicin use was protective. For all procedures, the variables associated with TF were haemoglobin < 10 g/dL, hip fracture and additional joint surgery not related to persistent infection. CONCLUSIONS: TF remains common in SA-PJI. Functional loss accounted for a substantial proportion of treatment failures, particularly after prosthesis removal. Use of rifampicin after DAIR was associated with a protective effect. Among the risk factors identified, anaemia and obesity have not frequently been reported in previous studies. TRIAL REGISTRATION: This study is registered at clinicaltrials.gov, registration no. NCT03826108.

Staphylococcus aureus is one of the most virulent bacteria and frequently causes prosthetic joint infections.Knowledge of the treatment of this type of infection has advanced in recent years, and treatment guidelines have led to improved management. Typically, the successful treatment of these infections has been determined by clinical cure, that is, the symptoms of infection have disappeared, but has not taken into account loss of function (such as significant difficulties walking), which is critical for the patient's quality of life. Our aim in this study was to evaluate the success of current management strategies for S. aureus prosthetic joint infection, including recovery of functionality, and the factors that predict why some of these infections are not cured, to identify areas for improvement.In a multinational cohort of 128 patients with S. aureus prosthetic joint infection, rates of treatment failure were found to be high, with significant rates of loss of function, especially when the prosthesis needed to be removed. Loss of function was less frequent when the infection was initially treated with surgical cleaning without removal of the prosthesis, even when this procedure failed at first. We found that anaemia and obesity were associated with lower treatment success, and that the probability of treatment success increased when surgical cleaning without prosthesis removal was performed early, and when the antibiotic rifampicin was used in combination with another antibiotic.

Preoperative and perioperative risk factors, and risk score development for prosthetic joint infection due to Staphylococcus aureus: a multinational matched case-control study.

OBJECTIVES: We aim to identify the preoperative and perioperative risk factors associated with post-surgical Staphylococcus aureus prosthetic joint infections (PJI) and to develop and validate risk-scoring systems, to allow a better identification of high-risk patients for more efficient targeted interventions. METHODS: We performed a multicenter matched case-control study of patients who underwent a primary hip and knee arthroplasty from 2014 to 2016. Two multivariable models by logistic regression were performed, one for the preoperative and one for perioperative variables; predictive scores also were developed and validated in an external cohort. RESULTS: In total, 130 cases and 386 controls were included. The variables independently associated with S. aureus-PJI in the preoperative period were (adjusted OR; 95% CI): body mass index >30 kg/m2 (3.0; 1.9 to 4.8), resident in a long-term care facility (2.8; 1.05 to 7.5), fracture as reason for arthroplasty (2.7; 1.4 to 5.03), skin disorders (2.5; 0.9 to 7.04), previous surgery in the index joint (2.4; 1.3 to 4.4), male sex (1.9; 1.2 to 2.9) and American Society of Anesthesiologists index score 3 to 4 (1.8; 1.2 to 2.9). The area under the receiver operating characteristic curve was 0.73 (95% CI 0.68 to 0.78). In perioperative model, the risk factors were the previous ones plus surgical antibiotic prophylaxis administered out of the first 60 minutes before incision (5.9; 2.1 to 16.2), wound drainage for >72 hours after arthroplasty (4.5; 1.9 to 19.4) and use of metal bearing material versus ceramic (1.9; 1.1 to 3.3). The area under the receiver operating characteristic curve was 0.78 (95% CI 0.72 to 0.83). The predictive scores developed were validated in the external cohort. DISCUSSION: Predictive scores for S. aureus-PJI were developed and validated; this information would be useful for implementation of specific preventive measures.

Examining the immune signatures of SARS-CoV-2 infection in pregnancy and the impact on neurodevelopment: Protocol of the SIGNATURE longitudinal study.

The COVID-19 pandemic represents a valuable opportunity to carry out cohort studies that allow us to advance our knowledge on pathophysiological mechanisms of neuropsychiatric diseases. One of these opportunities is the study of the relationships between inflammation, brain development and an increased risk of suffering neuropsychiatric disorders. Based on the hypothesis that neuroinflammation during early stages of life is associated with neurodevelopmental disorders and confers a greater risk of developing neuropsychiatric disorders, we propose a cohort study of SARS-CoV-2-infected pregnant women and their newborns. The main objective of SIGNATURE project is to explore how the presence of prenatal SARS-CoV-2 infection and other non-infectious stressors generates an abnormal inflammatory activity in the newborn. The cohort of women during the COVID-19 pandemic will be psychological and biological monitored during their pregnancy, delivery, childbirth and postpartum. The biological information of the umbilical cord (foetus blood) and peripheral blood from the mother will be obtained after childbirth. These samples and the clinical characterisation of the cohort of mothers and newborns, are tremendously valuable at this time. This is a protocol report and no analyses have been conducted yet, being currently at, our study is in the recruitment process step. At the time of this publication, we have identified 1,060 SARS-CoV-2 infected mothers and all have already given birth. From the total of identified mothers, we have recruited 537 SARS-COV-2 infected women and all of them have completed the mental health assessment during pregnancy. We have collected biological samples from 119 mothers and babies. Additionally, we have recruited 390 non-infected pregnant women.

Prognosis of unexpected positive intraoperative cultures in arthroplasty revision: A large multicenter cohort.

BACKGROUND: The positive-intraoperative-cultures-type prosthetic joint infection (PIOC-PJI) is considered when surgical cultures yield microorganisms in presumed aseptic arthroplasty revisions. Herein we assess the risk factors for failure in the largest cohort of PIOC-PJI patients reported to date. METHODS: A retrospective, observational, multicenter study was performed during 2007-2017. Surgeries leading to diagnose PIOC-PJI included only one-stage procedures with either complete or partial prosthesis revision. Failure was defined as recurrence caused by the same microorganism. RESULTS: 203 cases were included (age 72 years, 52% females). Coagulase-negative staphylococci (n = 125, 62%) was the main etiology, but some episodes were caused by virulent bacteria (n = 51, 25%). Prosthesis complete and partial revision was performed in 93 (46%) and 110 (54%) cases, respectively. After a median of 3.4 years, failure occurred in 17 episodes (8.4%, 95%CI 5.3-13.1). Partial revision was an independent predictor of failure (HR 3.63; 95%CI 1.03-12.8), adjusted for gram-negative bacilli (GNB) infection (HR 2.68; 95%CI 0.91-7.89) and chronic renal impairment (HR 2.40; 95%CI 0.90-6.44). Treatment with biofilm-active antibiotics (rifampin/fluoroquinolones) had a favorable impact on infections caused by staphylococci and GNB. CONCLUSION: Overall prognosis of PIOC-PJI is good, but close follow-up is required in cases of partial revision and in infections caused by GNB.

Impact of the COVID-19 Pandemic on Antimicrobial Consumption and Hospital-Acquired Candidemia and Multidrug-Resistant Bloodstream Infections.

During the COVID-19 pandemic, the implementation of antimicrobial stewardship strategies has been recommended. This study aimed to assess the impact of the COVID-19 pandemic in a tertiary care Spanish hospital with an active ongoing antimicrobial stewardship programme (ASP). For a 20-week period, we weekly assessed antimicrobial consumption, incidence density, and crude death rate per 1000 occupied bed days of candidemia and multidrug-resistant (MDR) bacterial bloodstream infections (BSI). We conducted a segmented regression analysis of time series. Antimicrobial consumption increased +3.5% per week (p = 0.016) for six weeks after the national lockdown, followed by a sustained weekly reduction of -6.4% (p = 0.001). The global trend for the whole period was stable. The frequency of empirical treatment of patients with COVID-19 was 33.7%. No change in the global trend of incidence of hospital-acquired candidemia and MDR bacterial BSI was observed (+0.5% weekly; p = 0.816), nor differences in 14 and 30-day crude death rates (p = 0.653 and p = 0.732, respectively). Our work provides quantitative data about the pandemic effect on antimicrobial consumption and clinical outcomes in a centre with an active ongoing institutional and education-based ASP. However, assessing the long-term impact of the COVID-19 pandemic on antimicrobial resistance is required.

Outpatient Parenteral Antimicrobial Treatment for Non-Cystic Fibrosis Bronchiectasis Exacerbations: A Prospective Multicentre Observational Cohort Study.

BACKGROUND: The recently published guidelines of the Spanish Society of Pulmonology and Thoracic Surgery encourage physicians to use outpatient antimicrobial therapy to treat exacerbations in patients with non-cystic fibrosis bronchiectasis (NCFB). The published literature on this topic, however, is scarce. METHODS: We report a prospective observational cohort study of patients with NCFB who received treatment at home for at least one exacerbation episode between September 2012 and September 2017 as part of an outpatient parenteral antimicrobial therapy (OPAT) program. Patients were included in the analysis if they fulfilled all of the following criteria: established diagnosis of bronchiectasis according to current guidelines criteria, clinical exacerbation, requiring intravenous antibiotics because of failure to respond to oral antibiotics, or isolation of a microorganism resistant to oral options. OBJECTIVES: To evaluate the effectiveness and safety of the treatment of patients with NCFB exacerbations in an OPAT program under "real-world" conditions. RESULTS: Sixty-seven patients were treated in the OPAT program due to bacterial exacerbations of NCFB. Forty-five (67.2%) patients were admitted to hospital for a median of 7 days before starting OPAT. Sixty-three (94%) patients achieved resolution of the exacerbation at the end of therapy. Four patients needed hospital readmission, and one died. The OPAT program saved 11,586 days of hospital admission, equivalent to EUR 7,866,904. CONCLUSIONS: OPAT appears to be a safe, effective, and efficient strategy for treating patients with exacerbations of NCFB.

Escherichia coli causing meningitis in an adult: A case report and experimental characterization of its virulence / Meningitis por Escherichia coli en un adulto: caso clínico y caracterización experimental de su virulencia

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The Different Microbial Etiology of Prosthetic Joint Infections according to Route of Acquisition and Time after Prosthesis Implantation, Including the Role of Multidrug-Resistant Organisms.

The aim of our study was to characterize the etiology of prosthetic joint infections (PJIs)-including multidrug-resistant organisms (MDRO)-by category of infection. A multicenter study of 2544 patients with PJIs was performed. We analyzed the causative microorganisms according to the Tsukayama's scheme (early postoperative, late chronic, and acute hematogenous infections (EPI, LCI, AHI) and "positive intraoperative cultures" (PIC)). Non-hematogenous PJIs were also evaluated according to time since surgery: <1 month, 2-3 months, 4-12 months, >12 months. AHIs were mostly caused by Staphylococcus aureus (39.2%) and streptococci (30.2%). EPIs were characterized by a preponderance of virulent microorganisms (S. aureus, Gram-negative bacilli (GNB), enterococci), MDROs (24%) and polymicrobial infections (27.4%). Conversely, coagulase-negative staphylococci (CoNS) and Cutibacterium species were predominant in LCIs (54.5% and 6.1%, respectively) and PICs (57.1% and 15.1%). The percentage of MDROs isolated in EPIs was more than three times the percentage isolated in LCIs (7.8%) and more than twice the proportion found in AHI (10.9%). There was a significant decreasing linear trend over the four time intervals post-surgery for virulent microorganisms, MDROs, and polymicrobial infections, and a rising trend for CoNS, streptococci and Cutibacterium spp. The observed differences have important implications for the empirical antimicrobial treatment of PJIs.

La formación de grado en enfermedades infecciosas, resistencia y uso de antibióticos desde la perspectiva de los estudiantes de Medicina / Perspective of Spanish medical students regarding undergraduate education in infectious diseases, bacterial resistance and antibiotic use

Introducción: Una de las principales herramientas para optimizar el uso de los antibióticos es la formación de los prescriptores. El objetivo de este trabajo es conocer la opinión de los estudiantes de Medicina españoles sobre la formación en enfermedades infecciosas. Material y métodos: Se distribuyó un cuestionario on line anonimizado entre estudiantes de sexto curso a través de distintos canales. El cuestionario incluyó 45 preguntas sobre conocimientos, actitudes y percepciones sobre el diagnóstico, resistencia antimicrobiana, uso de antibióticos y la formación de pregrado en enfermedades infecciosas. Resultados: Se recibieron un total de 441 encuestas de 21 facultades. Se obtuvieron 374 respuestas (84,8%) de las 8 facultades más representadas, con una tasa de respuesta del 28,9%. La mayoría de los alumnos se sentían preparados para identificar los signos clínicos de infección (418; 94,8%) y para interpretar correctamente las pruebas de laboratorio (382; 86,6%). Reconocieron saber elegir un antibiótico con seguridad sin consultar libros ni guías (178; 40,4%). Solo 107 alumnos (24,3%) consideraron haber recibido suficiente formación en el uso prudente de los antimicrobianos. Respecto a los métodos de aprendizaje, se percibieron como más útiles la discusión de casos clínicos, los rotatorios en servicios o unidades de enfermedades infecciosas y los talleres de pequeños grupos: se evaluaron favorablemente en un 76,9; en un 76 y en un 68,8% de los casos, respectivamente. Conclusión: Los estudiantes de Medicina se encuentran más seguros en el diagnóstico de enfermedades infecciosas que en el tratamiento antibiótico. Asimismo, sienten la necesidad de recibir mayor formación en antibioterapia y uso prudente en antibióticos

Introduction: One of the main tools to optimize antibiotics use is education of prescribers. The aim of this article is to study undergraduate education in the field of infectious diseases, antimicrobial resistance and antibiotic stewardship from the perspective of Spanish medical students. Material and methods: An anonymous online questionnaire was distributed among sixth grade students using different channels in Europe, within the ESGAP Student-Prepare survey. The questionnaire included 45 questions about knowledge, attitudes and perceptions about diagnosis, bacterial resistance, use of antibiotics and undergraduate training in infectious diseases. We present here the Spanish results. Results: A total of 441 surveys were received from 21 medical schools. A total of 374 responses (84.8%) were obtained from the 8 most represented faculties, with a response rate of 28.9%. Most students felt adequately prepared to identify clinical signs of infection (418; 94.8%) and to accurately interpret laboratory tests (382; 86.6%). A total of 178 (40.4%) acknowledged being able to choose an antibiotic with confidence without consulting books or guidelines. Only 107 (24.3%) students considered that they had received sufficient training in judicious use of antibiotics. Regarding learning methods, the discussion of clinical cases, infectious diseases units rotatories and small group workshops were considered the most useful, being evaluated favorably in 76.9%, 76% and 68.8% of the cases. Conclusion: Medical students feel more confident in the diagnosis of infectious diseases than in antibiotic treatment. They also feel the need to receive more training in antibiotics and judicious antibiotic use

Perspective of Spanish medical students regarding undergraduate education in infectious diseases, bacterial resistance and antibiotic use. / La formación de grado en enfermedades infecciosas, resistencia y uso de antibióticos desde la perspectiva de los estudiantes de Medicina.

INTRODUCTION: One of the main tools to optimize antibiotics use is education of prescribers. The aim of this article is to study undergraduate education in the field of infectious diseases, antimicrobial resistance and antibiotic stewardship from the perspective of Spanish medical students. MATERIAL AND METHODS: An anonymous online questionnaire was distributed among sixth grade students using different channels in Europe, within the ESGAP Student-Prepare survey. The questionnaire included 45 questions about knowledge, attitudes and perceptions about diagnosis, bacterial resistance, use of antibiotics and undergraduate training in infectious diseases. We present here the Spanish results. RESULTS: A total of 441 surveys were received from 21 medical schools. A total of 374 responses (84.8%) were obtained from the 8 most represented faculties, with a response rate of 28.9%. Most students felt adequately prepared to identify clinical signs of infection (418; 94.8%) and to accurately interpret laboratory tests (382; 86.6%). A total of 178 (40.4%) acknowledged being able to choose an antibiotic with confidence without consulting books or guidelines. Only 107 (24.3%) students considered that they had received sufficient training in judicious use of antibiotics. Regarding learning methods, the discussion of clinical cases, infectious diseases units rotatories and small group workshops were considered the most useful, being evaluated favorably in 76.9%, 76% and 68.8% of the cases. CONCLUSION: Medical students feel more confident in the diagnosis of infectious diseases than in antibiotic treatment. They also feel the need to receive more training in antibiotics and judicious antibiotic use.

Evaluation of the impact of a nationwide massive online open course on the appropriate use of antimicrobials.

Objectives: To evaluate the impact of a massive online open course (MOOC) design on the appropriate use of antimicrobial agents, to determine specific study areas with better learning outcomes and to identify weak points. Methods: A pre- and post-intervention study in the context of a training course on infectious diseases aimed at health professionals. We designed a questionnaire with 30 questions related to the management of infectious diseases in different clinical situations. Participants had to answer the questions based on their competencies and training for these situations. We analysed the scores obtained before and after the course and the resulting progress. In addition, an open response section was provided to enable a qualitative evaluation. Results: Two thousand one hundred and forty-eight health professionals were enrolled in the course. The questionnaire was completed before and after the course by 606 participants, mainly physicians (81.2%) and pharmacists (15.4%). The mean overall scores for the pre- and post-course questionnaires were 6.2 (SD 1.38) and 7.9 (SD 0.88), respectively (overall score increase = 1.8, SD 1.21, P < 0.001). A significant increase in self-assessment was detected (P < 0.001) for all the questions. Qualitative assessments were provided by 218 participants with 225 comments, most of which were very positive. Conclusions: The course with a MOOC design showed a great teaching capacity in the infectious diseases area for all the clinical situations analysed, notably in the management of severe infections with higher mortality. For future editions of this training activity, the need to include other infectious diseases, especially infections in primary care, was highlighted.

Long-Term Impact of an Educational Antimicrobial Stewardship Program on Hospital-Acquired Candidemia and Multidrug-Resistant Bloodstream Infections: A Quasi-Experimental Study of Interrupted Time-Series Analysis.

BACKGROUND: The global crisis of bacterial resistance urges the scientific community to implement intervention programs in healthcare facilities to promote an appropriate use of antibiotics. However, the clinical benefits or the impact on resistance of these interventions has not been definitively proved. METHODS: We designed a quasi-experimental intervention study with an interrupted time-series analysis. A multidisciplinary team conducted a multifaceted educational intervention in our tertiary-care hospital over a 5-year period. The main activity of the program consisted of peer-to-peer educational interviews between counselors and prescribers from all departments to reinforce the principles of the proper use of antibiotics. We assessed antibiotic consumption, incidence density of Candida and multidrug-resistant (MDR) bacteria bloodstream infections (BSIs) and their crude death rate per 1000 occupied bed days (OBDs). RESULTS: A quick and intense reduction in antibiotic consumption occurred 6 months after the implementation of the intervention (change in level, -216.8 defined daily doses per 1000 OBDs; 95% confidence interval, -347.5 to -86.1), and was sustained during subsequent years (average reduction, -19,9%). In addition, the increasing trend observed in the preintervention period for the incidence density of candidemia and MDR BSI (+0.018 cases per 1000 OBDs per quarter; 95% confidence interval, -.003 to .039) reverted toward a decreasing trend of -0.130 per quarter (change in slope, -0.029; -.051 to -.008), and so did the mortality rate (change in slope, -0.015; -.021 to -.008). CONCLUSIONS: This education-based antimicrobial stewardship program was effective in decreasing the incidence and mortality rate of hospital-acquired candidemia and MDR BSI through sustained reduction in antibiotic use.

Bacteraemia due to non-ESBL-producing Escherichia coli O25b:H4 sequence type 131: insights into risk factors, clinical features and outcomes.

The epidemiology and outcomes of bloodstream infections (BSIs) caused by Escherichia coli ST131 isolates not producing extended-spectrum ß-lactamases (ESBLs) are not well defined despite being more prevalent than ESBL-producers. In this study, risk factors and the impact on outcome of BSIs caused by non-ESBL-producing ST131 E. coli versus non-ST131 E. coli were investigated. A case-control study was performed in two tertiary centres to identify risk factors for ST131. Molecular methods were used to investigate all E. coli isolates from blood cultures for those belonging to O25b:H4-ST131 clonal group. fimH alleles were characterised in ST131 isolates. Multivariate analysis was performed by logistic regression or Cox regression as appropriate. A total of 33 ST131 E. coli cases and 56 controls were studied. ST131 isolates showed higher rates of resistance to ampicillin and ciprofloxacin; fimH alleles were H30 in 14 isolates (42.4%) and H22 in 12 isolates (36.4%). Only recent surgery (OR = 7.03, 95% CI 1.71-28.84; P = 0.007) and unknown source of bacteraemia (OR = 5.37, 95% CI 0.93-30.81; P = 0.05) were associated with ST131. ST131 isolates showed no association with 30-day mortality, therapeutic failure, presentation with severe sepsis/shock or length of stay. Bacteraemia due to non-ESBL-producing O25b:H4-ST131 E. coli showed few differences in terms of risk factors as well as similar outcome to non-ST131 E. coli. These data support the notion that ST131 strains are not less clinically virulent despite showing increased antimicrobial resistance, but also that they are not more virulent than other clonal groups causing BSI.

Enfermedad recurrente por Clostridium difficile ribotipo 027 / Recurrent disease due to ribotype 027 Clostridium difficile

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Impact of the MIC of piperacillin/tazobactam on the outcome for patients with bacteraemia due to Enterobacteriaceae: the Bacteraemia-MIC project.

OBJECTIVE: Our objective was to evaluate the impact of low versus borderline MIC of piperacillin/tazobactam on the clinical outcomes of patients with bacteraemia caused by Enterobacteriaceae who were treated with that antimicrobial. PATIENTS AND METHODS: A prospective observational multicentre cohort study was conducted in 13 Spanish university hospitals. Patients >17 years old with bacteraemia due to Enterobacteriaceae who received empirical piperacillin/tazobactam treatment for at least 48 h were included. Outcome variables were clinical response at day 21, clinical response at end of treatment with piperacillin/tazobactam and all-cause 30 day mortality. Univariate and multivariate logistic regression analyses were performed. RESULTS: Overall, 275 patients were included in the analysis; 248 (90.2%) in the low MIC group (≤ 4 mg/L) and 27 (9.8%) in the borderline MIC group (8-16 mg/L). The biliary tract was the most common source of infection (48.4%) and Escherichia coli was the most frequent pathogen (63.3%). Crude 30 day mortality rates were 10.5% and 11.1% for the low MIC group and the borderline MIC group, respectively (relative risk = 1.06, 95% CI = 0.34-3.27, P = 1). Multivariate analysis of failure at day 21 and at end of treatment with piperacillin/tazobactam and 30 day mortality showed no trend towards increased clinical failure or mortality with borderline MICs (OR = 0.96, 95% CI = 0.18-4.88, P = 0.96; OR = 0.47, 95% CI = 0.10-2.26, P = 0.35; OR = 1.48, 95% CI = 0.33-6.68, P = 0.6). CONCLUSIONS: We did not find that higher piperacillin/tazobactam MIC within the susceptible or intermediate susceptibility range had a significant influence on the outcome for patients with bacteraemia due to Enterobacteriaceae.