Risk factors for piperacillin-tazobactam-resistant Pseudomonas aeruginosa among hospitalized patients

Evaluation of intravenous amoxicillin-clavulanate use in two Canadian hospitals

We describe our experience with intravenous amoxicillin-clavulanate, which is new to the Canadian market. The majority of patients were successfully de-escalated from piperacillin-tazobactam or a carbapenem for respiratory infections or skin and soft tissue infections. Intravenous amoxicillin-clavulanate provides a good alternative in an era of rising Pseudomonas aeruginosa resistance.

Prevalence of Pseudomonas aeruginosa and its antibiotic resistance in patients who have received Hematopoietic Stem-Cell Transplantation; A globally Systematic Review

Gram-negative bacteria are infectious and life-threatening agents after hematopoietic stem cell transplantation (HSCT). So, this study aimed to investigate the prevalence of Pseudomonas aeruginosa and its antibiotic resistance in patients who have received Hematopoietic Stem-Cell Transplantation through a systematic review. The systematic search was done with key words; Pseudomonas aeruginosa, hematopoietic stem cell transplantation from 2000 to the end of July 2023 in Google Scholar and PubMed/Medline, Scopus, and Web of Science. Twelve studies were able to include our study. Quality assessment of studies was done by Appraisal tool for Cross-Sectional Studies. The most of the included studies were conducted as allo-HSCT. Infections such as respiratory infection, urinary infection and bacteremia have occurred. The rate of prevalence with P. aeruginosa has varied between 3 and 100%. The average age of the participants was between 1 and 74 years. The rate of prevalence of P. aeruginosa resistant to several drugs has been reported to be variable, ranging from 20 to 100%. The highest antibiotic resistance was reported against cefotetan (100%), and the lowest was related to tobramycin (1.8%) followed by amikacin, levofloxacin and ciprofloxacin with the prevalence of 16.6%. Our findings showed a high prevalence and antibiotic resistance rate of P. aeruginosa in Hematopoietic stem cell transplantation. Therefore, more serious health measures should be taken in patients after transplantation.

Impact of the cefazolin shortage on the selection and cost of parenteral antibiotics during the supply disruption period in Japan: A controlled interrupted time series analysis

BACKGROUND

A serious shortage of cefazolin (CEZ) occurred in Japan in 2019. We compared the impact of the CEZ shortage on the selection of parenteral antibiotics at affected and non-affected hospitals.

METHODS

The data were extracted from a nationwide Japanese administrative database and included all hospitalized cases between April 2016 and December 2020. We defined 'hospitals with shortage' as those hospitals with a statistically significant decrease in the use of CEZ during the supply disruption period compared to the same months of the previous year; other hospitals as 'hospitals without shortage'. We determined the proportion of each selected parenteral antibiotic use to the sum of all selected antibiotic use in the two groups of hospitals during the supply disruption period and during the same months of the previous year. A controlled interrupted time series (CITS) analysis was conducted to estimate the impact of the CEZ shortage on each antibiotic use and the cost of all parenteral antibiotics per patient day in hospitals with shortage as compared to those without shortage.

RESULTS

In the hospitals with shortage, the proportion of CEZ use to the sum of all selected antibiotics decreased (23.5-11.1%). The decrease in CEZ use was mainly offset by the use of ceftriaxone, ceftriaxone, and ampicillin/sulbactam. The CITS analysis showed a statistically significant increase in the use of broader-spectrum beta-lactams and clindamycin during the supply disruption period (flomoxef up 58.1%, cefotiam up 63.1%, cefmetazole up 14.5%, ceftriaxone up 13.9%, and clindamycin up 20.1%). The analysis showed no statistically significant change in the cost of all parenteral antibiotics per patient day.

CONCLUSIONS

During the CEZ supply disruption, there was a statistically significant increase in the use of broader-spectrum beta-lactams and clindamycin in hospitals with shortage compared with those without shortage.

Dimerization of 600 Da branched polyethylenimine improves β-lactam antibiotic potentiation against antibiotic-resistant Staphylococcus epidermidis and Pseudomonas aeruginosa

Antibiotic resistance is a growing concern in the medical field. Drug-susceptible infections are often treated with β-lactam antibiotics, which bind to enzymes known as penicillin-binding proteins (PBPs). When the PBPs are disabled, the integrity of the cell wall is compromised, leading to cell lysis. Resistance renders β-lactam antibiotics ineffective, and clinicians turn to be more effective, but often more toxic, antibiotics. An alternative approach is combining antibiotics with compounds that disable resistance mechanisms. Previously, we have shown that low-molecular-weight 600 Da branched polyethylenimine restores β-lactam susceptibility to Gram-positive and Gram-negative pathogens with antibiotic resistance. In this study, this approach is extended to the homodimers of 600 Da BPEI that have improved potentiation properties compared to monomers of 600 Da BPEI and 1200 Da BPEI. The homodimers are synthesized by linking two 600 Da BPEI molecules with methylenebisacrylamide (MBAA). The resulting product was characterized with FTIR spectroscopy, ¹ H NMR spectroscopy, checkerboard microbroth dilution assays, and cell toxicity assays. These data show that the 600 Da BPEI homodimer is more effective than 1200 Da BPEI toward the potentiation of oxacillin against methicillin-resistant Staphylococcus epidermidis and the potentiation of piperacillin against Pseudomonas aeruginosa.

Pilot study evaluating intravenous amoxicillin-clavulanate as an alternative to piperacillin-tazobactam for general surgery patients

In this point-prevalence survey followed by prospective audit and feedback at 4 tertiary-care hospitals in Calgary, Alberta, Canada, we evaluated whether intravenous amoxicillin-clavulanate may be used as a narrower-spectrum alternative to intravenous piperacillin-tazobactam for patients admitted to general surgery services.

Risk Factors for the Acquisition of Enterococcus faecium Infection and Mortality in Patients with Enterococcal Bacteremia: A 5-Year Retrospective Analysis in a Tertiary Care University Hospital

The incidence of bacteremia caused by Enterococcus faecium, which is highly resistant to multiple antibiotics, is increasing in Japan. However, risk factors for the acquisition of E. faecium infection and mortality due to enterococcal bacteremia are not well known. We compared demographic, microbiological, and clinical characteristics using a Cox regression model and univariate analysis. We performed a multivariate analysis to identify risk factors for patients treated between 2014 and 2018. Among 186 patients with enterococcal bacteremia, two groups included in the Kaplan–Meier analysis (E. faecalis (n = 88) and E. faecium (n = 94)) showed poor overall survival in the E. faecium group (HR: 1.92; 95% confidence interval: 1.01–3.66; p = 0.048). The median daily antibiotic cost per patient in the E. faecium group was significantly higher than that in the E. faecalis group ($23 ($13–$34) vs. $34 ($22–$58), p < 0.001). E. faecium strains were more frequently identified with previous use of antipseudomonal penicillins (OR = 4.04, p < 0.001) and carbapenems (OR = 3.33, p = 0.003). Bacteremia from an unknown source (OR = 2.79, p = 0.025) and acute kidney injury (OR = 4.51, p = 0.004) were associated with higher risks of 30-day mortality in patients with enterococcal bacteremia. Therefore, clinicians should provide improved medical management, with support from specialized teams such as those assisting antimicrobial stewardship programs.

Antimicrobial and Anti-Biofilm Activities of Citrus sinensis and Moringa oleifera Against the Pathogenic Pseudomonas aeruginosa and Staphylococcus aureus

Context The plant Moringa oleifera Lam (Moringaceae), generally termed as drumstick tree, and Citrus sinensis Linn (Rutaceae) fruit have the ability to treat multiple human infections. A biofilm is none other than a complicated microbial community whose nature is greatly resistant to antimicrobial elements. The development of biofilms in abiotic and biotic surfaces has a connection with higher levels of mortality and morbidity. Along with that, it is regarded as a vital element of bacterial pathogenicity. Aim The present study evaluated the inhibitory effect and anti-biofilm activity of Moringa oleifera (M. oleifera) and Citrus sinensis (C. sinensis) extracts against those of pathogenic Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) . Materials and methods Two plant materials were collected from the local market of Tabuk city and two human pathogenic microbial strains were used in the study: S. aureus and P. aeruginosa. Further, a series of morphological, physiological, and conventional biochemical tests were performed to identify the selected microorganisms. In addition to this, the study conducted the following tests: antibiotic sensitivity test, extended-spectrum β-lactamase (ESβL), and methicillin-resistant Staphylococcus aureus (MRSA) production, biofilm formation in 96-well microtiter plates, minimum inhibitory concentration (MIC) determination, the effect of sub-MICs of C. sinensis extract and M. oleifera extract on the viability of test bacteria, and finally, measurement of the inhibition of biofilm. Results A remarkable result of the research is that the peel extract of C. sinensisand the flesh extract of M. oleifera efficiently inhibited biofilm formation by the addition of sub-inhibitory concentrations of (1/16 x MIC - 1/2 x MIC) MRSA and ESBL, respectively. P. aeruginosa shows high resistance to piperacillin (85.0%). Similarly, the resistance of MRSA was also high (65%) against gentamycin and amikacin antibiotics. Regarding ESBL, 12 (60%) isolates showed confirmed positive and 45% of S. aureus showed MRSA activity. On observing the 12 ESβL-positive P. aeruginosa, it was found that five strains (PS1, PS4, PS6, PS8, and PS11) have formed strong biofilm, methicillin-resistant S. aureus while four strains showed strong biofilm activity (SA2, SA4, SA5, and SA8). The MIC of C. sinensis extract and M. oleifera extract against strong biofilm producers had a range of 50-2000 µg/ml concentration after overnight incubation. The study results revealed that the antibiofilm activity comparatively showed the extract of M. oleifera was better than C. sinensisagainst the mixed culture (PS1+SA8, PS6+SA2, and PS8+SA4). Hence, it is recommended to use M. oleifera as an option to monitor the development of microbial biofilms or as a model for looking for better medicines. Conclusion The presence of antimicrobial activity found in M. oleifera and C. sinensis extracts offers convincing evidence of their likely action as antimicrobial metabolites against the studied microorganism. Anti-biofilm assay findings have shown that M. oleifera and C. sinensis extracts have effectively blocked MRSA and ESBL development in the biofilm matrix.

Evaluating the appropriateness of carbapenem and piperacillin-tazobactam prescribing in a tertiary care hospital in Saudi Arabia

Background

Antimicrobial resistance (AMR) is presently considered an emergent major global public health concern and excessive and/or inappropriate use of broad-spectrum antimicrobials contribute to the development of AMR.

Objective

To evaluate the appropriateness of carbapenems and piperacillin-tazobactam use in a tertiary care hospital.

Methods

A retrospective, observational, cross-sectional, drug-utilization study was conducted. The study included all adult hospitalized patients who had received at least one dose of the antimicrobials during their admission for the period between 1 January 2016 and 31 December 2017. The appropriateness of antimicrobial therapy was evaluated according to the Infectious Diseases Society of America (IDSA) guidelines with the consideration of the institutional antibiogram.

Results

Overall, 2731 patients received 5005 courses with one of the antimicrobials, for a total of 5045.9 defined daily doses (DDD) of imipenem-cilastatin, 6492.3 of meropenem and 15,595 of piperacillin-tazobactam (4.93, 6.34 and 15.24 DDD/100 bed days, respectively). The mean age of the patients who received either antimicrobial was 55.5 ± 20.3 years, with a 14-day average length of hospital stay. About half (52%) of the prescriptions were written for patients treated in the medical ward. Pneumonia (26.6%) and sepsis (24.9%) were the most common indication for the initiation of antimicrobial therapy. Of the assessed prescriptions, only 2787 (56.5%) were prescribed appropriately, with 2142 (43.5%) deemed inappropriate. The three most common reasons for inappropriate prescription were: the spectrum of activity was too broad (44.6%), followed by antimicrobial use without culture request (32.4%), and failure of suitable antimicrobial de-escalation (19.9%).

Conclusions

The study indicates that the overall rate of inappropriateness was high, emphasizing the need to develop initiatives to effectively improve broad-spectrum antimicrobial prescribing.

Five-year surveillance and correlation of antibiotic consumption and resistance of Gram-negative bacteria at an intensive care unit in Serbia

A surveillance study was performed in an intensive care unit in the largest tertiary health care center in Vojvodina, Serbia from 2014 to 2018. Antibiotic prescription data were collated in the WHO anatomical therapeutic chemical (ATC)/defined daily dose (DDD) format, while antibiotic resistance was expressed as incidence density adjusted for total inpatient-days. Individual trends were determined by linear regression, while possible associations between antibiotic prescription and resistance were evaluated using cross-correlation analysis. An overall decrease in antibiotic utilization was observed. The prescription rates of piperacillin-tazobactam increased significantly, while consumption of 3rd and 4th generation cephalosporins and fluoroquinolones decreased. There were rising incidence densities of doripenem resistant Acinetobacter spp., piperacillin-tazobactam resistant Pseudomonas aeruginosa and carbapenem and colistin resistant Klebsiella pneumoniae. These results can serve as a basis for the development of antimicrobial stewardship strategies in the current setting.

Changes of resistance rates in Pseudomonas aeruginosa strains are unrelated to antimicrobial consumption in ICU populations with invasive device-related infection

OBJECTIVE

To evaluate the relationship between antipseudomonal antibiotic consumption and each individual drug resistance rate in Pseudomonas aeruginosa strains causing ICU acquired invasive device-related infections (IDRI).

DESIGN

A post hoc analysis was made of the data collected prospectively from the ENVIN-HELICS registry.

SETTING

Intensive Care Units participating in the ENVIN-UCI registry between the years 2007 and 2016 (3-month registry each year).

PATIENTS

Patients admitted for over 24h.

MAIN VARIABLES

Annual linear and nonlinear trends of resistance rates of P. aeruginosa strains identified in IDRI and days of treatment of each antipseudomonal antibiotic family per 1000 occupied ICU bed days (DOT) were calculated.

RESULTS

A total of 15,095 episodes of IDRI were diagnosed in 11,652 patients (6.2% out of a total of 187,100). Pseudomonas aeruginosa was identified in 2095 (13.6%) of 15,432 pathogens causing IDRI. Resistance increased significantly over the study period for piperacillin-tazobactam (P<0.001), imipenem (P=0.016), meropenem (P=0.004), ceftazidime (P=0.005) and cefepime (P=0.015), while variations in resistance rates for amikacin, ciprofloxacin, levofloxacin and colistin proved nonsignificant. A significant DOT decrease was observed for aminoglycosides (P<0.001), cephalosporins (P<0.001), quinolones (P<0.001) and carbapenems (P<0.001).

CONCLUSIONS

No significant association was observed between consumption of each antipseudomonal antibiotic family and the respective resistance rates for P. aeruginosa strains identified in IDRI.

Measuring Appropriate Antibiotic Prescribing in Acute Hospitals: Development of a National Audit Tool Through a Delphi Consensus

This study developed a patient-level audit tool to assess the appropriateness of antibiotic prescribing in acute National Health Service (NHS) hospitals in the UK. A modified Delphi process was used to evaluate variables identified from published literature that could be used to support an assessment of appropriateness of antibiotic use. At a national workshop, 22 infection experts reached a consensus to define appropriate prescribing and agree upon an initial draft audit tool. Following this, a national multidisciplinary panel of 19 infection experts, of whom only one was part of the workshop, was convened to evaluate and validate variables using questionnaires to confirm the relevance of each variable in assessing appropriate prescribing. The initial evidence synthesis of published literature identified 25 variables that could be used to support an assessment of appropriateness of antibiotic use. All the panel members reviewed the variables for the first round of the Delphi; the panel accepted 23 out of 25 variables. Following review by the project team, one of the two rejected variables was rephrased, and the second neutral variable was re-scored. The panel accepted both these variables in round two with a 68% response rate. Accepted variables were used to develop an audit tool to determine the extent of appropriateness of antibiotic prescribing at the individual patient level in acute NHS hospitals through infection expert consensus based on the results of a Delphi process.

Risk factors for hospitalized patients with resistant or multidrug-resistant Pseudomonas aeruginosa infections: a systematic review and meta-analysis

Background

Identifying risk factors predicting acquisition of resistant Pseudomonas aeruginosa will aid surveillance and diagnostic initiatives and can be crucial in early and appropriate antibiotic therapy. We conducted a systematic review examining risk factors of acquisition of resistant P. aeruginosa among hospitalized patients.

Methods

MEDLINE®, EMBASE®, and Cochrane Central were searched between 2000 and 2016 for studies examining independent risk factors associated with acquisition of resistant P. aeruginosa, among hospitalized patients. Random effects model meta-analysis was conducted when at least three or more studies were sufficiently similar.

Results

Of the 54 eligible articles, 28 publications (31studies) examined multi-drug resistant (MDR) or extensively drug resistant (XDR) P. aeruginosa and 26 publications (29 studies) examined resistant P. aeruginosa. The acquisition of MDR P. aeruginosa, as compared with non-MDR P. aeruginosa, was significantly associated with intensive care unit (ICU) admission (3 studies: summary adjusted odds ratio [OR] 2.2) or use of quinolones (4 studies: summary adjusted OR 3.59). Acquisition of MDR or XDR compared with susceptible P. aeruginosa was significantly associated with prior hospital stay (4 studies: summary adjusted OR 1.90), use of quinolones (3 studies: summary adjusted OR 4.34), or use of carbapenems (3 studies: summary adjusted OR 13.68). The acquisition of MDR P. aeruginosa compared with non-P. aeruginosa was significantly associated with prior use of cephalosporins (3 studies: summary adjusted OR 3.96), quinolones (4 studies: summary adjusted OR 2.96), carbapenems (6 studies: summary adjusted OR 2.61), and prior hospital stay (4 studies: summary adjusted OR 1.74). The acquisition of carbapenem-resistant P. aeruginosa compared with susceptible P. aeruginosa, was statistically significantly associated with prior use of piperacillin-tazobactam (3 studies: summary adjusted OR 2.64), vancomycin (3 studies: summary adjusted OR 1.76), and carbapenems (7 studies: summary adjusted OR 4.36).

Conclusions

Prior use of antibiotics and prior hospital or ICU stay was the most significant risk factors for acquisition of resistant P. aeruginosa. These findings provide guidance in identifying patients that may be at an elevated risk for a resistant infection and emphasize the importance of antimicrobial stewardship and infection control in hospitals.

Clinical efficacy of piperacillin/tazobactam in the treatment of complicated skin and soft tissue infections

INTRODUCTION

Complicated skin and soft tissue infections (cSSTIs) are skin and soft tissue infections (SSTIs) that involve deep soft tissue. cSSTIs often require surgical intervention and/or hospitalization. cSSTIs are associated with significant mortality and morbidity, and carry a significant burden on health care systems. Piperacillin/tazobactam has been regarded as a standard treatment for cSSTIs because of its antibiotic spectrum, safety and clinical efficacy. Several antibiotics, as compared to piperacillin/tazobactam, have been evaluated in the treatment of cSSTIs. Areas covered: This review summarizes randomized controlled trials (RCTs) evaluating the clinical efficacy of piperacillin/tazobactam for the treatment of cSSTIs. Expert opinion: Piperacillin/tazobactam, which covers most causative organisms in cSSTIs, is the drug of choice for the treatment of cSSTIs. Other options such as ertapenem and moxifloxacin may be reasonable where multiple daily dosing or intravenous administration is inappropriate. But in general, they should be avoided as an empirical treatment because of their highly association with resistant bacteria, which are becoming a global threat. Therefore, piperacilin/tazobactam is appropriate as an empirical therapy for the treatment of SSTIs and should be de-escalated as soon as causative organisms are identified, their drug-sensitivity results are available, and clinical condition becomes stable.

Evaluation of Risk Factors for Antibiotic Resistance in Patients with Nosocomial Infections Caused by Pseudomonas aeruginosa

Background. Pseudomonas aeruginosa (P. aeruginosa) is resistant to various antibiotics and can cause serious nosocomial infections with high morbidity and mortality. In this clinical study, we investigated the risk factors in patients who were diagnosed with P. aeruginosa-related nosocomial infection. Methods. A retrospective case control study including patients with P. aeruginosa-related nosocomial infection. Patients who were resistant to any of the six antibiotics (imipenem, meropenem, piperacillin-tazobactam, ciprofloxacin, amikacin, and ceftazidime) constituted the study group. Results. One hundred and twenty isolates were isolated. Various risk factors were detected for each antibiotic in the univariate analysis. In the multivariate analysis, previous cefazolin use was found as an independent risk factor for the development of imipenem resistance (OR = 3.33; CI 95% [1.11–10.0]; p = 0.03), whereas previous cerebrovascular attack (OR = 3.57; CI 95% [1.31–9.76]; p = 0.01) and previous meropenem use (OR = 4.13; CI 95% [1.21–14.07]; p = 0.02) were independent factors for the development of meropenem resistance. For the development of resistance to ciprofloxacin, hospitalization in the neurology intensive care unit (OR = 4.24; CI 95% [1.5–11.98]; p = 0.006) and mechanical ventilator application (OR = 11.7; CI 95% [2.24–61.45]; p = 0.004) were independent risk factors. Conclusion. The meticulous application of contact measures can decrease the rate of nosocomial infections.

The Importance of Addressing Multidrug Resistance and Not Assuming Single-Drug Resistance in Case-Control Studies

Background.

Case-control studies analyzing antibiotic exposure as a risk factor for antimicrobial resistance usually assume single-drug resistance in the bacteria under study, even though resistance to multiple antimicrobials may be present. Since antibiotic selection pressures differ depending on the susceptibility profile of the antimicrobial-resistant bacteria, an accurate assessment of whether exposure to an individual antimicrobial is a risk factor for the emergence of resistance should distinguish between single-drug–resistant and multidrug-resistant bacteria.

Objective.

To determine whether the exposures to individual antibiotics that were identified as independent risk factors in case-control studies differed depending on whether single-drug–resistant or multidrug-resistant bacteria were evaluated.

Design.

Two retrospective case-control studies were performed with data on patients harboringPseudomonas aeruginosastrains resistant only to ciprofloxacin (CRPA) and patients harboringP. aeruginosastrains resistant to ciprofloxacin and other antibiotics (multidrug-resistantP. aeruginosa[MDR-PA]). These 2 groups were compared with patients not harboringP. aeruginosa.

Setting.

Two tertiary care hospitals.

Results.

A total of 41 patients harboring CRPA and 151 patients harboring MDR-PA were identified and matched to 192 control subjects. By conditional logistic regression, independent risk factors associated with presence of CRPA were nonambulatory status (OR, 5.6 [95% confidence interval {CI}, 1.4-23];P= .02) and prior ciprofloxacin exposure (OR, 5.0 [95% CI, 1.2-21];P= .03). Independent risk factors for presence of MDR-PA were a Charlson score greater than 2 (OR, 3.3 [95% CI 1.8-6.0];P<.001) and exposure to quinolones (OR, 2.8 [95% CI, 1.2-5.0];P= .001), third- and fourth-generation cephalosporins (OR, 3.5 [95% CI, 1.7-7.1];P<.001), imipenem (OR, 3.8 [95% CI, 1.2-12.1];P= .02), and/or aminoglycosides (OR, 2.3 [95% CI, 1.04-5.1];P= .04).

Conclusion.

There were substantial differences in exposure to individual antimicrobials between patients harboring CRPA and patients harboring MDR-PA. Future case-control studies addressing risk factors for single-drug–resistant bacteria should consider the complete susceptibility profile of the bacteria under investigation.

Impact of Severity of Illness Bias and Control Group Misclassification Bias in Case-Control Studies of Antimicrobial-Resistant Organisms

Background:

Case-control studies often analyze risk factors for antibiotic resistance. Recently published articles have illustrated that randomly selected control-patients may be preferable to those with the susceptible phenotype of the organism. A possible methodologic problem with randomly selected control-patients is potential bias due to control group misclassification. This occurs if some control-patients did not have clinical cultures performed and thus might have been unidentified case-patients. If this bias exists, these studies might be expected to report lower odds ratios (ORs) because control-patients would be more like case-patients.

Objective:

To analyze potential biases that might arise due to control group misclassification and potentially larger selection biases that may be introduced if control-patients are required to have at least one clinical culture.

Patients:

One hundred twenty case-patients, 770 control-patients in group 1, and 510 control-patients in group 2.

Methods:

Two case-control studies. Case-patients had clinical cultures positive for imipenem-resistant Pseudomonas aeruginosa. The first group of control-patients were random. The second group of control-patients were identical to those in group 1 except being required to have at least one clinical culture.

Results:

Univariate analyses showed higher ORs for case-patients versus control-patients in group 1 (imipenem [OR, 12.5], piperacillin-tazobactam [OR, 3.7], and vancomycin [OR, 4.7]) as compared with case-patients versus control-patients in group 2 (imipenem [OR, 8.0], piperacillin-tazobactam [OR, 2.5], and vancomycin [OR, 3.0]).

Conclusion:

Requiring control-patients to have at least one clinical culture introduces a selection bias likely because it eliminates patients with less severe illness.

Pseudomonas aeruginosa: targeting cell-wall metabolism for new antibacterial discovery and development

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections and is resistant to most antibiotics. With therapeutic options against P. aeruginosa dwindling, and the lack of new antibiotics in advanced developmental stages, strategies for preserving the effectiveness of current antibiotics are urgently required. β-Lactam antibiotics are important agents for treating P. aeruginosa infections, thus, adjuvants that potentiate the activity of these compounds are desirable for extending their lifespan while new antibiotics - or antibiotic classes - are discovered and developed. In this review, we discuss recent research that has identified exploitable targets of cell-wall metabolism for the design and development of compounds that hinder resistance and potentiate the activity of antipseudomonal β-lactams.

Amoxicillin plus temocillin as an alternative empiric therapy for the treatment of severe hospital-acquired pneumonia: results from a retrospective audit

A formulary decision was made at a large provider of acute hospital services in Surrey to replace piperacillin/tazobactam with amoxicillin+temocillin for the empiric treatment of severe hospital-acquired pneumonia. This decision was made because the use of broad-spectrum-β-lactam antibiotics is a known risk factor for Clostridium difficile infection (CDI) and for the selection of resistance. After the antibiotic formulary was changed, a retrospective audit was conducted to assess the effect of this change. Data from patients hospitalised between January 2011 and July 2012 for severe hospital-acquired pneumonia and treated empirically with piperacillin/tazobactam or amoxicillin+temocillin were reviewed retrospectively. Clinical characteristics of patients, data related to the episode of pneumonia, clinical success and incidence of significant diarrhoea and CDI were analysed. One hundred ninety-two episodes of severe hospital-acquired pneumonia in 188 patients were identified from hospital records. Ninety-eight patients received piperacillin/tazobactam and 94 amoxicillin+temocillin. At baseline, the two treatment groups were comparable, except that more patients with renal insufficiency were treated with piperacillin/tazobactam. Clinical success was comparable (80 versus 82 %; P = 0.86), but differences were observed between piperacillin/tazobactam and amoxicillin+temocillin for the rates of significant diarrhoea (34 versus 4 %, respectively; P < 0.0001) and for CDI (7 versus 0 %, respectively; P < 0.0028). This preliminary study suggests that the combination amoxicillin+temocillin is a viable alternative to piperacillin/tazobactam for the treatment of severe hospital-acquired pneumonia. This combination appears to be associated with fewer gastrointestinal adverse events. Further studies are needed to evaluate the place of amoxicillin+temocillin as empiric treatment of severe hospital-acquired pneumonia.

Acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically ill medical patients: role of colonization pressure and antibiotic exposure

INTRODUCTION

The objective of this work was to investigate the risk factors for the acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically ill patients, taking into account colonization pressure.

METHODS

We conducted a prospective cohort study in an 8-bed medical intensive care unit during a 35-month period. Nasopharyngeal and rectal swabs and respiratory secretions were obtained within 48 hours of admission and thrice weekly thereafter. During the study, a policy of consecutive mixing and cycling periods of three classes of antipseudomonal antibiotics was followed in the unit.

RESULTS

Of 850 patients admitted for ≥ 3 days, 751 (88.3%) received an antibiotic, 562 of which (66.1%) were antipseudomonal antibiotics. A total of 68 patients (8%) carried P. aeruginosa upon admission, and among the remaining 782, 104 (13%) acquired at least one strain of P. aeruginosa during their stay. Multivariate analysis selected shock (odds ratio (OR) = 2.1; 95% confidence interval (CI), 1.2 to 3.7), intubation (OR = 3.6; 95% CI, 1.7 to 7.5), enteral nutrition (OR = 3.6; 95% CI, 1.8 to 7.6), parenteral nutrition (OR = 3.9; 95% CI, 1.6 to 9.6), tracheostomy (OR = 4.4; 95% CI, 2.3 to 8.3) and colonization pressure >0.43 (OR = 4; 95% CI, 1.2 to 5) as independently associated with the acquisition of P. aeruginosa, whereas exposure to fluoroquinolones for >3 days (OR = 0.4; 95% CI, 0.2 to 0.8) was protective. In the whole series, prior exposure to carbapenems was independently associated with carbapenem resistance, and prior amikacin use predicted piperacillin-tazobactam, fluoroquinolone and multiple-drug resistance.

CONCLUSIONS

In critical care settings with a high rate of antibiotic use, colonization pressure and non-antibiotic exposures may be the crucial factors for P. aeruginosa acquisition, whereas fluoroquinolones may actually decrease its likelihood. For the acquisition of strains resistant to piperacillin-tazobactam, fluoroquinolones and multiple drugs, exposure to amikacin may be more relevant than previously recognized.

Risk factors for gyrA and parC mutations in Pseudomonas aeruginosa

OBJECTIVE

The major mechanism of fluoroquinolone (FQ) resistance in Pseudomonas aeruginosa (PSA) is modification of target proteins in DNA gyrase and topoisomerase IV, most commonly the gyrA and parC subunits. The objective of this study was to determine risk factors for PSA with and without gyrA or parC mutations.

DESIGN

Case-case-control study

SETTING

Two adult academic acute-care hospitals

PATIENTS

Case 1 study participants had a PSA isolate on hospital day 3 or later with any gyrA or parC mutation; case 2 study participants had a PSA isolate on hospital day 3 or later without these mutations. Controls were a random sample of all inpatients with a stay of 3 days or more.

METHODS

Each case group was compared to the control group in separate multivariate models on the basis of demographics and inpatient antibiotic exposure, and risk factors were qualitatively compared.

RESULTS

Of 298 PSA isolates, 172 (57.7%) had at least 1 mutation. Exposure to vancomycin and other agents with extended Gram-positive activity was a risk factor for both cases (case 1 odds ratio [OR], 1.09; 95% confidence interval [CI], 1.04-1.13; OR, 1.14; 95% CI, 1.03-1.26; case 2 OR, 1.09; 95% CI, 1.03-1.14; OR, 1.13; 95% CI, 1.01-1.25, respectively).

CONCLUSIONS

Exposure to agents with extended Gram-positive activity is a risk factor for isolation of PSA overall but not for gyrA/parC mutations. FQ exposure is not associated with isolation of PSA with mutations.

Risk Factors for and Impact of Infection or Colonization With Aztreonam-Resistant Pseudomonas aeruginosa

Objective.

To identify risk factors for infection or colonization with aztreonam-resistant Pseudomonas aeruginosa and examine the impact of this organism on mortality.

Design.

A case-control study was performed to identify risk factors for infection or colonization with aztreonam-resistant P. aeruginosa. A cohort study was subsequently performed to examine the impact of aztreonam resistance on outcomes.

Setting.

A tertiary referral center in southeastern Pennsylvania.

Participants.

Inpatients with a clinical culture positive for P. aeruginosa between January 1, 1999, and December 31, 2000.

Results.

Of 720 P. aeruginosa, isolates, 183 (25.4%) were aztreonam-resistant and 537 (74.6%) were aztreonam susceptible. In a multivariable model, prior fluoroquinolone use (adjusted odds ratio [aOR], 1.81 [95% confidence interval {CI}, 1.17-2.80]), prior use of an antianaerobic agent (aOR, 1.56 [95% CI, 1.06-2.29]), and renal insufficiency (aOR, 1.59 [95% CI, 1.10-2.29]) were associated with infection or colonization with aztreonam-resistant P. aeruginosa, while older age (aOR, 0.98 [95% CI, 0.97-0.99] per year of age) was negatively associated with infection or colonization with this organism. In-hospital mortality was higher among subjects infected or colonized with aztreonam-resistant P. aeruginosa, compared with those who were infected or colonized with aztreonam-susceptible P. aeruginos (25.7% vs 16.8%;P = .009), but in multivariable analysis, no significant association was found between infection or colonization with aztreonam-resistant P. aeruginosa and mortality.

Conclusions.

Curbing the use of fluoroquinolones and antimicrobials with antianaerobic activity may be an effective strategy to limit the emergence of aztreonam-resistant P. aeruginosa.

Relationship between ceftolozane-tazobactam exposure and selection for Pseudomonas aeruginosa resistance in a hollow-fiber infection model

It is important to understand the relationship between antibiotic exposure and the selection of drug resistance in the context of therapy exposure. We sought to identify the ceftolozane-tazobactam exposure necessary to prevent the amplification of drug-resistant bacterial subpopulations in a hollow-fiber infection model. Two Pseudomonas aeruginosa challenge isolates were selected for study, a wild-type ATCC strain (ceftolozane-tazobactam MIC, 0.5 mg/liter) and a clinical isolate (ceftolozane-tazobactam MIC, 4 mg/liter). The experiment duration was 10 days, and the ceftolozane-tazobactam dose ratio (2:1) and dosing interval (every 8 h) were selected to approximate those expected to be used clinically. The studied ceftolozane-tazobactam dosing regimens ranged from 62.5/31.25 to 2,000/1,000 mg per dose in step fold dilutions. Negative-control arms included no treatment and tazobactam at 500 mg every 8 h. Positive-control arms included ceftolozane at 1 g every 8 h and piperacillin-tazobactam dosed at 4.5 g every 6 h. For the wild-type ATCC strain, resistance was not selected by any ceftolozane-tazobactam regimen evaluated. For the clinical isolate, an inverted-U-shaped function best described the relationship between the amplification of a drug-resistant subpopulation and drug exposure. The least (62.5/31.25 mg) and most (2,000/1,000 mg) intensive ceftolozane-tazobactam dosing regimens did not select for drug resistance. Drug resistance selection was observed with intermediately intensive dosing regimens (125/62.5 through 1,000/500 mg). For the intermediately intensive ceftolozane-tazobactam dosing regimens, the duration until the selection for drug resistance increased with dose regimen intensity. These data support the selection of ceftolozane-tazobactam dosing regimens that minimize the potential for on-therapy drug resistance selection.

Risk factors for infection with multidrug-resistant bacteria in non-ventilated patients with hospital-acquired pneumonia

OBJECTIVE:

To identify risk factors for the development of hospital-acquired pneumonia (HAP) caused by multidrug-resistant (MDR) bacteria in non-ventilated patients.

METHODS:

This was a retrospective observational cohort study conducted over a three-year period at a tertiary-care teaching hospital. We included only non-ventilated patients diagnosed with HAP and presenting with positive bacterial cultures. Categorical variables were compared with chi-square test. Logistic regression analysis was used to determine risk factors for HAP caused by MDR bacteria.

RESULTS:

Of the 140 patients diagnosed with HAP, 59 (42.1%) were infected with MDR strains. Among the patients infected with methicillin-resistant Staphylococcus aureus and those infected with methicillin-susceptible S. aureus, mortality was 45.9% and 50.0%, respectively (p = 0.763). Among the patients infected with MDR and those infected with non-MDR gram-negative bacilli, mortality was 45.8% and 38.3%, respectively (p = 0.527). Univariate analysis identified the following risk factors for infection with MDR bacteria: COPD; congestive heart failure; chronic renal failure; dialysis; urinary catheterization; extrapulmonary infection; and use of antimicrobial therapy within the last 10 days before the diagnosis of HAP. Multivariate analysis showed that the use of antibiotics within the last 10 days before the diagnosis of HAP was the only independent predictor of infection with MDR bacteria (OR = 3.45; 95% CI: 1.56-7.61; p = 0.002).

CONCLUSIONS:

In this single-center study, the use of broad-spectrum antibiotics within the last 10 days before the diagnosis of HAP was the only independent predictor of infection with MDR bacteria in non-ventilated patients with HAP.

Risk factors for carbapenem-resistant Klebsiella pneumoniae infection/colonization: a case-case-control study

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is increasingly reported worldwide. The aim of the present study was to identify risk factors associated with the development of CRKP infections. A retrospective, case-case-control study was performed at the University Hospital of Heraklion, Greece. The study population included 83 patients from whom CRKP was isolated, 79 from whom carbapenem-sensitive K. pneumoniae (CSKP) was isolated and 161 (control group) from whom K. pneumoniae was not isolated. The median age of CRKP and CSKP patients was 79 (28-101) and 80 (39-97) years, respectively, while that of the controls was 75 (18-100) years. K. pneumoniae was isolated predominantly from urine in both case groups, followed by blood. Independent risk factors for CRKP infection/colonization were admission to ICU (p = 0.004), prior surgical procedure (p = 0.036) and presence of renal disease (p = 0.037), while for CSKP were neurological disease (p = 0.007), and older age (p = 0.011). No association between CRKP and prior antimicrobial exposure was found. Of the entire cohort 40 patients (12%) died; 22 (27%) in the CRKP, 12 (15%) in the CSKP and 6 (4%) in the control group. Isolation of any K. pneumoniae strain was associated with higher mortality compared to the control group (21% vs. 4%; p < 0.005). Mortality was not statistically different between those infected/colonized/with a CRKP or a CSKP strain (p = 0.084). According to these results prior ICU stay, prior surgical procedure and renal disease were independent risk factors for the development of a CRKP infection/colonization.

Altered pharmacokinetics of piperacillin in febrile neutropenic patients with hematological malignancy

This study assessed the pharmacokinetics and dosing adequacy of piperacillin in febrile neutropenic patients after the first dose. Pharmacokinetic analysis was performed using noncompartmental methods. We observed an elevated volume of distribution (29.7 ± 8.0 liters [mean ± standard deviation]) and clearance (20.2 ± 7.5 liters/h) compared to data from other patient populations. Antibiotic exposure did not consistently result in therapeutic targets. We conclude that alternative dosing strategies guided by therapeutic drug monitoring may be required to optimize exposure.

Epidemiological interpretation of studies examining the effect of antibiotic usage on resistance

Bacterial resistance to antibiotics is a growing clinical problem and public health threat. Antibiotic use is a known risk factor for the emergence of antibiotic resistance, but demonstrating the causal link between antibiotic use and resistance is challenging. This review describes different study designs for assessing the association between antibiotic use and resistance and discusses strengths and limitations of each. Approaches to measuring antibiotic use and antibiotic resistance are presented. Important methodological issues such as confounding, establishing temporality, and control group selection are examined.

The role of antimicrobial stewardship in curbing carbapenem resistance

Antimicrobial resistance is a continuing, growing, worldwide iatrogenic complication of modern medical care. Carbapenem resistance among certain pathogens poses a significant challenge. In order to reduce the spread of these nearly untreatable pathogens, preventative efforts should be directed at reducing patient-to-patient transmission and preventing the emergence of resistance among susceptible strains. One theoretical intervention to reduce the emergence of resistance is establishing and strictly adhering to an antimicrobial stewardship program. However, data pertaining to the direct effect of stewardship in curtailing carbapenem resistance among epidemiologically significant organisms are scarce. In this report, we review the potential biases associated with data interpretation in this research field, and we review the data pertaining to the impact of stewardship in curbing carbapenem resistance in three significant groups of pathogens: Pseudomonas aeruginosa, Enterobacteriaceae and Acinetobacter baumannii.

Outbreak of multi-drug resistant Pseudomonas aeruginosa bloodstream infection in the haematology unit of a South African Academic Hospital

Objective

To describe an outbreak of multi-resistant Pseudomonas aeruginosa bloodstream infections (MRPA-BSI) that occurred in the haematology ward of a tertiary academic hospital in Cape Town, South Africa, and determine risk factors for acquisition of MRPA-BSI.

Methods

The outbreak investigation included a search for additional cases, review of patient records, environmental and staff screening, molecular typing using pulsed-field gel electrophoresis (PFGE) and Multi-locus sequencing (MLST) and a retrospective case-control study.

Results

Ten MRPA-BSI cases occurred in the haematology ward between January 2010 and January 2011. The case fatality rate was 80%. Staff screening specimens were negative for MRPA and an environmental source was not identified. PFGE showed that 9/10 isolates were related. MLST showed that 3 of these 9 isolates belonged to Sequence type (ST) 233 while the unrelated isolate belonged to ST260.

Conclusion

We have described an outbreak of MRPA-BSI occurring over an extended period of time among neutropenic haematology patients. Molecular typing confirms that the outbreak was predominantly due to a single strain. The source of the outbreak was not identified, but the outbreak appears to have been controlled following intensive infection control measures.

Time series analysis as a tool to predict the impact of antimicrobial restriction in antibiotic stewardship programs using the example of multidrug-resistant Pseudomonas aeruginosa

The association between antimicrobial consumption and resistance in nonfermentative Gram-negative bacteria is well-known. Antimicrobial restriction, implemented in clinical routines by antibiotic stewardship programs (ASPs), is considered a means to reduce resistance rates. Whether and how antimicrobial restriction can accomplish this goal is still unknown though. This leads to an element of uncertainty when designing strategies for ASPs. From January 2002 until December 2011, an observational study was performed at the University Hospital Tübingen, Tübingen, Germany, to investigate the association between antimicrobial use and resistance rates in Pseudomonas aeruginosa. Transfer function models were used to determine such associations and to simulate antimicrobial restriction strategies. Various positive associations between antimicrobial consumption and resistance were observed in our setting. Surprisingly, impact estimations of different antimicrobial restriction strategies revealed relatively low intervention expenses to effectively attenuate the observed increase in resistance. For example, a simulated intervention of an annual 4% reduction in the use of meropenem over 3 years from 2009 until 2011 yielded a 62.5% attenuation (95% confidence interval, 15% to 110%) in the rising trend of multidrug-resistant Pseudomonas aeruginosa (three- and four-class-resistant P. aeruginosa [34MRGN-PA]). Time series analysis models derived from past data may be a tool to predict the outcome of antimicrobial restriction strategies, and could be used to design ASPs.

Outcomes of health care-associated pneumonia empirically treated with guideline-concordant regimens versus community-acquired pneumonia guideline-concordant regimens for patients admitted to acute care wards from home

BACKGROUND

The introduction of the health care-associated pneumonia (HCAP) categorization expanded recommendations for broad-spectrum empiric antibiotics to pneumonia patients presenting from the community with recent health care-system exposure. However, the efficacy of such regimens in improving clinical outcomes in these patients has not been well established.

OBJECTIVE

To compare the clinical outcomes of HCAP patients treated initially with HCAP guideline-concordant antibiotic regimens to those treated initially with community-acquired pneumonia (CAP) guideline-concordant antibiotic regimens.

METHODS

This retrospective study included HCAP patients presenting from home and admitted to general medical wards. HCAP regimen patients were treated empirically with at least 1 antipseudomonal agent. All other patients were assigned to the CAP regimen group. The primary end point was clinical cure at 30 days postdischarge. Subgroup analysis was performed in patients hospitalized 1-30 days and 31-90 days before the HCAP admission.

RESULTS

Of 228 HCAP admissions, 122 patients received CAP regimens and 106 received HCAP regimens. The 2 groups were similar at baseline, including Pneumonia Severity Index scores. Attributable clinical cure occurred in 75.4% of CAP regimen patients and 69.8% of HCAP regimen patients (p = 0.34). Overall clinical cure occurred in 59.8% of CAP regimen patients and 54.7% of HCAP regimen patients (p = 0.44). The CAP regimen group used fewer days of intravenous antibiotics (4.39 vs 7.75, p < 0.0001) and had shorter lengths of stay (6.36 vs 8.58 days, p < 0.0001). For patients hospitalized 31-90 days earlier, clinical cure was higher in the CAP regimen group (attributable, 82.9% vs 60.0%, p = 0.0090; overall, 67.1% vs 47.5%, p = 0.044).

CONCLUSIONS

Compared to CAP guideline-concordant regimens, treatment of HCAP with HCAP guideline-concordant regimens did not increase clinical cure rates and was associated with lower clinical cure rates in patients hospitalized 31-90 days prior to the HCAP admission. This study suggests that broad-spectrum empiric antibiotics may not be necessary in all HCAP patient groups.

"Swimming in resistance": Co-colonization with carbapenem-resistant Enterobacteriaceae and Acinetobacter baumannii or Pseudomonas aeruginosa

BACKGROUND

Co-colonization of patients with carbapenem-resistant Enterobacteriaceae (CRE) and Acinetobacter baumannii (AB) or Pseudomonas aeruginosa (PA) is reported to be associated with increased antibiotic resistance and mortality.

METHODS

CREs isolated between September 2008 and September 2009 were analyzed at Detroit Medical Center. Patients who had an additional isolation of AB or PA during the period spanning 7 days before to 7 days after CRE isolation were considered co-colonized. Molecular typing was used to determine genetic similarity among CRE strains.

RESULTS

Eighty-six unique patient isolates of CREs were analyzed. Thirty-four patients (40%) were co-colonized, and 26 (79%) had AB or PA isolated on the same day as the CRE. High Charlson Comorbidity Index score was an independent predictor for co-colonization. Recent stay at a long-term acute-care facility and previous therapy with antimicrobials with activity only against gram-positive microorganisms also were associated with co-colonization, but did not remain significant independent predictors. Co-colonization was associated with higher levels of resistance to carbapenems among CREs and increased 90-day mortality. Molecular typing revealed CRE polyclonality in co-colonized patients.

CONCLUSIONS

Co-colonization is found in patients with the greatest disease burden in the hospital and occurs due to the dissemination of multiple CRE strains. This finding calls into question the practice of cohorting patients with CRE in close proximity to patients with AB or PA.

Multi-drug-resistant gram-negative bacterial infection in surgical patients hospitalized in the ICU: a cohort study

We sought to identify risk factors for postoperative infections, caused by multi-drug-resistant gram-negative bacteria (MDR-GNB) in surgical patients. This was a retrospective cohort study among patients hospitalized in the intensive care unit (ICU) for more than 5 days, following general surgical operations. Comparison of patients who developed infection caused by MDR-GNB with the remainder of the cohort showed that every minute of operative time, use of special treatments during hospitalization (antineoplastic, immunosuppressive or immunomodulating therapies), every day of metronidazole, and every day of carbapenems use, increased patients' odds to acquire an infection caused by MDR-GNB by 0.7%, 8.9 times, 9%, and 9%, respectively [OR (95% CI): 1.007 (1.003-1.011), p = 0.001; 8.9 (1.8-17.3), p = 0.004; 1.09 (1.04-1.18), p = 0.039; 1.09 (1.01-1.18), p = 0.023, respectively]. The above were adjusted in the multivariable analysis for the confounder of time distribution of infections caused by MDR-GNB. Finally, the secondary comparison, with patients that did not develop any infection, showed that patients who had received antibiotics, within 3 months prior to admission, had 3.8 times higher odds to acquire an infection caused by MDR-GNB [OR (95% CI): 3.8 (1.07-13.2), p = 0.002]. This study depicts certain, potentially modifiable, risk factors for postoperative infections in patients hospitalized in the ICU for more than 5 days.

The impact of Contact Isolation on the quality of inpatient hospital care

Background

Contact Isolation is a common hospital infection prevention method that may improve infectious outcomes but may also hinder healthcare delivery.

Methods

To evaluate the impact of Contact Isolation on compliance with individual and composite process of care quality measures, we formed four retrospective diagnosis-based cohorts from a 662-bed tertiary-care medical center. Each cohort contained patients evaluated for one of four Centers for Medicare and Medicaid Services (CMS) Hospital Compare process measures including Acute Myocardial Infarction (AMI), Congestive Heart Failure (CHF), Pneumonia (PNA) and Surgical Care Improvement Project (SCIP) from January 1, 2007 through May 30, 2009.

Results

The 6716-admission cohort included 1259 with AMI, 834 with CHF, 1377 with PNA and 3246 in SCIP. Contact Isolation was associated with not meeting 4 of 23 individual hospital measures (4 of 10 measures were not met for care provided while patients are typically isolated). Contact Isolation was independently associated with lower compliance with the composite pneumonia process-of-care measure (OR 0.3, 95% CI 0.1–0.7). AMI, CHF and SCIP composite measures were not impacted by Contact Isolation.

Conclusions

Contact Isolation was associated with lower adherence to some pneumonia quality of care process measures of care on inpatient wards but did not impact CHF, AMI or SCIP measures.

Impact of ureido/carboxypenicillin resistance on the prognosis of ventilator-associated pneumonia due to Pseudomonas aeruginosa

Introduction

Although Pseudomonas aeruginosa is a leading pathogen responsible for ventilator-associated pneumonia (VAP), the excess in mortality associated with multi-resistance in patients with P. aeruginosa VAP (PA-VAP), taking into account confounders such as treatment adequacy and prior length of stay in the ICU, has not yet been adequately estimated.

Methods

A total of 223 episodes of PA-VAP recorded into the Outcomerea database were evaluated. Patients with ureido/carboxy-resistant P. aeruginosa (PRPA) were compared with those with ureido/carboxy-sensitive P. aeruginosa (PSPA) after matching on duration of ICU stay at VAP onset and adjustment for confounders.

Results

Factors associated with onset of PRPA-VAP were as follows: admission to the ICU with septic shock, broad-spectrum antimicrobials at admission, prior use of ureido/carboxypenicillin, and colonization with PRPA before infection. Adequate antimicrobial therapy was more often delayed in the PRPA group. The crude ICU mortality rate and the hospital mortality rate were not different between the PRPA and the PSPA groups. In multivariate analysis, after controlling for time in the ICU before VAP diagnosis, neither ICU death (odds ratio (OR) = 0.73; 95% confidence interval (CI): 0.32 to 1.69; P = 0.46) nor hospital death (OR = 0.87; 95% CI: 0.38 to 1.99; P = 0.74) were increased in the presence of PRPA infection. This result remained unchanged in the subgroup of 87 patients who received adequate antimicrobial treatment on the day of VAP diagnosis.

Conclusions

After adjustment, and despite the more frequent delay in the initiation of an adequate antimicrobial therapy in these patients, resistance to ureido/carboxypenicillin was not associated with ICU or hospital death in patients with PA-VAP.

Previous ciprofloxacin exposure is associated with resistance to beta-lactam antibiotics in subsequent Pseudomonas aeruginosa bacteremic isolates

BACKGROUND

Pseudomonas aeruginosa cross-resistance to ceftazidime, imipenem, meropenem, piperacillin, and fluoroquinoles has been shown in experimental studies, but information regarding its impact in the clinical setting is scarce and inconsistent. The aim of this study was to assess whether previous exposure to ciprofloxacin influences on the sensitivity of those antibiotics in subsequent P aeruginosa bacteremic isolates.

METHODS

Patients with P aeruginosa bacteremia were recorded from a blood culture surveillance program (1997-2007). Demographic characteristics, underlying diseases, setting of the infection, source of infection, previous antibiotic exposure, and antibiotic sensitivity were analyzed.

RESULTS

We studied 572 cases of P aeruginosa bacteremia. There were 327 men (57.2%), and the mean age was 61.2 +/- 18 years. The bacteremia was nosocomial in 62.4% of episodes. Resistance rates of P aeruginosa isolates were 15.5% for ceftazidime, 16.7% for imipenem, 11.2% for meropenem, 12.3% for piperacillin-tazobactam, and 23.1% for ciprofloxacin. Exposure to ciprofloxacin during the previous 30 days was an independent predictor of resistance to ceftazidime (odds ratio [OR], 3; 95% confidence interval [CI]: 1.7-5.3; P < .001), imipenem (OR, 2; 95% CI: 1.1-3.7; P = .02), meropenem (OR, 2.7; 95% CI: 1.4-5.3; P = .004), piperacillin-tazobactam (OR, 2.4; 95% CI: 1.3-4.7; P = .007), ciprofloxacin (OR, 2.9; 95% CI: 1.7-4.9; P < .001), and multidrug resistance (OR, 2.5; 95% CI: 1.2-5.2; P = .02).

CONCLUSION

P aeruginosa bacteremic isolates from patients who have been exposed to ciprofloxacin during the 30 days prior to the development of bacteremia have an increased risk of being resistant to ceftazidime, imipenem, meropenem, piperacillin-tazobactam, or ciprofloxacin and to have multidrug resistance.

[Evolution of antimicrobial resistance against Pseudomonas aeruginosa in a French university hospital between 2002 and 2006]

AIM OF STUDY

Monitor evolution of antibiotic resistance of Pseudomonas aeruginosa from 2002 to 2006 in our hospital to optimize antibiotherapy.

PATIENTS AND METHOD

The infections/colonizations with P. aeruginosa have been identified by the hospital's informatic database. Bacteriological samples realized 48hours after patient's admission was considered as nosocomial. A Cochran-Armitage test was conducted to assess the evolution of resistance.

RESULTS

During this period, 2098 infections/colonizations with P. aeruginosa have been identified. Bacteriological samples (68.5%) were nosocomial. Among the beta-lactam antibiotics, ceftazidime and imipenem were the most active (R=16.8% and 15.2%, respectively), followed by piperacillin and piperacillin-tazobactam (R=24.8%, 18.4%, respectively). Amikacin and tobramycin were more active than gentamicin (R=19.9%; 22.2% and 40.6%, respectively). 28.9% of strains were resistant to ciprofloxacin. Nosocomial strains were significantly more resistant than non-hospital strains: ceftazidime: 17.9% versus 14.2%, p=0.0346; ticarcillin-clavulanic acid: 47.5% versus 39.6%, p=0.0009; piperacillin-tazobactam: 20.0% versus 14.8%, p=0.0046; ciprofloxacin: 30.7% versus 25.2%, p=0.0112. A significant increase in the resistance of nosocomial strains to ceftazidime, ticarcillin-clavulanic acid and piperacillin-tazobactam was noted. Resistance from non-hospital strains to fluoroquinolones, aminoglycosides, ceftazidime, piperacillin and ticarcillin-clavulanic acid decreased significantly.

CONCLUSION

P. aeruginosa is a predominantly nosocomial microorganism. There is a decrease of resistance for non-hospital strains. But the resistance of nosocomial strains to antibiotics widely prescribed in hospital is worrying.

Identifying risk factors for infections: the role of meta-analyses

Systematic review and meta-analysis are assuming greater importance in influencing policy makers and clinical opinion worldwide. Many discussions and publications have considered the merits of meta-analysis of epidemiologic data.50 Some observers suggest that meta-analysis of observational studies should be abandoned altogether. 51 In the authors' opinion, statistical combination of observational studies should not be a primary goal of a review. Analysis of heterogeneity between longitudinal studies, however, would provide more insights than mathematical calculation of the summary risk. Meta-analyses of risk factors for infections should strictly follow guidelines for meta-analyses of observational studies. A study protocol should be written in advance, completed literature searches performed, and studies selected in a reproducible and objective fashion. Biologic plausibility must be addressed. The reported findings should be interpreted with caution, taking into account the limitations of various methodologic aspects of risk factors studies. An important role for meta-analyses in this field would be to clarify hypotheses to be formulated for future Identifying Risk Factors for Infections 221 studies and stress limitations strictly related to studies on risk factors for bacterial and viral infections.

Influence of antipseudomonal agents on Pseudomonas aeruginosa colonization and acquisition of resistance in critically ill medical patients

OBJECTIVE

To assess the role of antipseudomonal agents on Pseudomonas aeruginosa colonization and acquisition of resistance.

DESIGN

Prospective cohort study.

SETTING

Two medical intensive care units.

PATIENTS AND PARTICIPANTS

346 patients admitted for >or= 48 h.

INTERVENTION

Analysis of data from an 8-month study comparing a mixing versus a cycling strategy of antibiotic use.

MEASUREMENTS AND RESULTS

Surveillance cultures from nares, pharynx, rectum, and respiratory secretions were obtained thrice weekly. Acquisition of resistance was defined as the isolation, after 48 h of ICU stay, of an isolate resistant to a given antibiotic if culture of admission samples were either negative or positive for a susceptible isolate. Emergence of resistance refers to the conversion of a defined pulsotype from susceptible to non-susceptible. Forty-four (13%) patients acquired 52 strains of P. aeruginosa. Administration of piperacillin-tazobactam for >or= 3 days (OR 2.6, 95% CI 1.09-6.27) and use of amikacin for >or= 3 days (OR 2.6, 95% CI 1.04-6.7) were positively associated with acquisition of P. aeruginosa, whereas use of quinolones (OR 0.27, 95% CI 0.1-0.7) and antipseudomonal cephalosporins (OR 0.27, 95% CI 0.08-0.9) was protective. Exposure to quinolones and cephalosporins was not associated with the acquisition of resistance, whereas it was linked with usage of all other agents. Neither quinolones nor cephalosporins were a major determinant on the emergence of resistance to themselves, as resistance to these antibiotics developed at a similar frequency in non-exposed patients.

CONCLUSIONS

In critically ill patients, quinolones and antipseudomonal cephalosporins may prevent the acquisition of P. aeruginosa and may have a negligible influence on the acquisition and emergence of resistance.

Summer Peaks in the Incidences of Gram-Negative Bacterial Infection Among Hospitalized Patients

OBJECTIVE

Recognition of seasonal trends in hospital infections may improve diagnosis, use of empirical therapy, and infection prevention interventions. There are very few data available regarding the seasonal variability of these infections. We quantified the seasonal variation in the incidences of hospital infection caused by common bacterial pathogens and estimated the association between temperature changes and infection rates.

METHODS

A cohort of all adult patients admitted to the University of Maryland Medical Center during the period from 1998 through 2005 was analyzed. Time-series analyses were used to estimate the association of the number of infections per month caused by Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacter cloacae, Escherichia coli, Staphylococcus aureus, and enterococci with season and temperature, while controlling for long-term trends.

RESULTS

There were 218,594 admissions to the index hospital, and analysis of 26,624 unique clinical cultures that grew the organisms of interest identified increases in the mean monthly rates of infection caused by P. aeruginosa (28% of isolates recovered; P ! .01), E. cloacae (46%; P ! .01), E. coli (12%; P ! .01), and A. baumannii (21%; Pp.06). For each 10 degrees F increase, we observed a 17% increase in the monthly rates of infection caused by P. aeruginosa (Pp.01) and A. baumanii (Pp.05).

CONCLUSION

Significantly higher rates of gram-negative infection were observed during the summer months, compared with other seasons. For some pathogens, higher temperatures were associated with higher infection rates, independent of seasonality. These findings have important implications for infection prevention, such as enhanced surveillance during the warmer months, and for choice of empirical antimicrobial therapy among hospitalized adults. Future, quasi-experimental investigations of gram-negative infection prevention initiatives should control for seasonal variation.

Impact of empiric antibiotic therapy on outcomes in patients with Pseudomonas aeruginosa bacteremia

The impact of appropriate empirical antimicrobial therapy for Pseudomonas aeruginosa bacteremia on patient outcomes has not been clearly established. We assessed the effect of appropriate empirical therapy on in-hospital mortality and length of stay (LOS) among patients with P. aeruginosa bacteremia. This was a retrospective cohort study of inpatients with a positive blood culture for P. aeruginosa between January 2001 and June 2005. Empirical therapy was defined as appropriate if the patient received an antibiotic the organism was susceptible to between 8 h before culture collection and the time the susceptibility results were available. The severity of the illness was measured 24 h before culture collection. The data were analyzed using logistic regression (in-hospital mortality) and linear regression (LOS). Overall, there were 167 episodes of P. aeruginosa bacteremia, 123 (86%) of which received appropriate empirical antibiotics. Sixty-one patients died (36.5%). The median time from culture collection to susceptibility results was 3.4 days. After we adjusted for age, severity of illness, and time at risk, we found that the appropriate empirical therapy was not significantly associated with mortality (odds ratio = 0.96; 95% confidence interval = 0.31 to 2.93). There was a 7% reduction in the mean LOS for patients who had received appropriate therapy at the time susceptibility results were available compared to those who did not (P = 0.74). These data suggest that the use of appropriate empirical therapy, i.e., before susceptibility results are known may not be as critical to patient outcomes as other studies have suggested.

How to fight antimicrobial resistance

Antimicrobial misuse results in the development of resistance and superbugs. Over recent decades, resistance has been increasing despite continuing efforts to control it, resulting in increased mortality and cost. Many authorities have proposed local, regional and national guidelines to fight against this phenomenon, and the usefulness of these programmes has been evaluated. Multifaceted intervention seems to be the most efficient method to control antimicrobial resistance. Monitoring of bacterial resistance and antibiotic use is essential, and the methodology has now been homogenized. The implementation of guidelines and infection control measures does not control antimicrobial resistance and needs to be reinforced by associated measures. Educational programmes and rotation policies have not been evaluated sufficiently in the literature. Combination antimicrobial therapy is inefficient in controlling antimicrobial resistance.

Impact of piperacillin resistance on the outcome of Pseudomonas ventilator-associated pneumonia

BACKGROUND

The impact of antibiotic resistance on the outcome of infections due to Gram-negative bacilli, especially Pseudomonas, remains highly controversial. STUDY OBJECTIVE, DESIGN, AND PATIENTS: We evaluated the impact of piperacillin resistance on the outcomes of Pseudomonas aeruginosa ventilator-associated pneumonia (VAP) for patients who had received appropriate empiric antibiotics before enrollment in the PNEUMA trial, a multicenter randomized study comparing 8 vs 15 days of antibiotics.

RESULTS

Despite similar characteristics at intensive care unit (ICU) admission, patients infected with piperacillin-resistant Pseudomonas strains were more acutely ill at VAP onset and had a higher 28-day mortality rate (37 vs 19%; P = 0.04) than those with piperacillin-susceptible Pseudomonas VAP. Factors associated with 28-day mortality retained by multivariable analysis were: age (OR: 1.07; 95% CI: 1.03-1.12); female gender (OR: 4.00; 95% CI: 1.41-11.11); severe underlying comorbidities (OR: 2.73; 95% CI: 1.02-7.33); and SOFA score (OR: 1.17; 95% CI: 1.03-1.32), but piperacillin resistance did not reach statistical significance (OR: 2.00; 95% CI: 0.72-5.61). The VAP recurrence rates, either superinfection or relapse, and durations of mechanical ventilation and ICU stay did not differ as a function of Pseudomonas-resistance status.

CONCLUSIONS

For patients with Pseudomonas VAP benefiting from appropriate empiric antibiotics, piperacillin resistance was associated with increased disease severity at VAP onset and higher 28-day crude mortality; however, after controlling for confounders, piperacillin-resistance was no longer significantly associated with 28-day mortality. The VAP recurrence rates and durations of ICU stay and mechanical ventilation did not differ for susceptible and resistant strains.

Antibiotic regimens and intestinal colonization with antibiotic-resistant gram-negative bacilli

The intestinal tract provides an important reservoir for antibiotic-resistant gram-negative bacilli, including Enterobacteriaceae species, Pseudomonas aeruginosa, and Acinetobacter baumannii. Selective pressure exerted by antibiotics plays a crucial role in the emergence and dissemination of these pathogens. Many classes of antibiotics may promote intestinal colonization by health care-associated gram-negative bacilli, because the organisms are often multidrug resistant. Antibiotics may inhibit colonization by gram-negative pathogens that remain susceptible, but the benefits of this effect are often limited because of the emergence of resistance. Antibiotic formulary alterations and standard infection control measures have been effective in controlling outbreaks of colonization and infection with antibiotic-resistant gram-negative pathogens. Additional research is needed to clarify the role of strategies such as selective decontamination of the digestive tract and decontamination of environmental surfaces and of patients' skin and wounds.

Comorbidity risk-adjustment measures were developed and validated for studies of antibiotic-resistant infections

OBJECTIVES

Comorbidities are often included in risk-factor models for nosocomial antibiotic-resistant bacterial infections, and aggregate comorbidity measures are valuable because they allow one variable to represent many. This study aimed to develop new aggregate comorbidity measures based upon the Chronic Disease Score (CDS) for assessing the comorbidity-attributable risk of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) nosocomial infections.

STUDY DESIGN AND SETTING

For each outcome, two retrospective cohort studies of hospitalized patients were conducted. Outcomes were a first MRSA or VRE positive clinical culture obtained 48 hours or more postadmission. Each cohort was divided into development (July 1998-2001) and validation (August 2001-2003) samples. New comorbidity measures were created for MRSA (CDS-MRSA), VRE (CDS-VRE), or any nosocomial infection outcome (CDS-ID) using logistic regression and subsequently validated. Model discrimination was measured using the c-statistic.

RESULTS

Discrimination of the CDS-MRSA (c=0.60), CDS-VRE (c=0.65), and CDS-ID (MRSA: c=0.57; VRE: c=0.64) was greater than that of the original CDS (MRSA: c=0.52; VRE: c=0.57).

CONCLUSION

The CDS-MRSA, CDS-VRE, and CDS-ID are new infectious disease specific comorbidity risk-adjustment measures that will be useful for the quality of future epidemiologic studies of MRSA, VRE, and other infectious diseases.