Predicting hospital rates of fluoroquinolone-resistant Pseudomonas aeruginosa from fluoroquinolone use in US hospitals and their surrounding communities

Strategies to Address Appropriate Fluoroquinolone Use in the Hospital

Purpose

Strategies to optimally use fluoroquinolones in the hospital setting are reviewed.

Summary

Fluoroquinolones possess broad-spectrum antimicrobial coverage and are widely used to treat a variety of infections including some serious, life-threatening conditions. Overuse and inappropriate use of fluoroquinolones has led to rapid emergence of fluoroquinolone-resistant organisms as well as multidrug-resistant pathogens. Preserving the fluoroquinolone class is important, especially given the lack of new antibiotics currently in clinical development. Maintaining the fluoroquinolone class as a therapeutic option requires the successful implementation of guidelines to promote appropriate, optimal use of these agents. Among many recommendations to control the growing problem of antimicrobial resistance, antimicrobial stewardship programs offer the most comprehensive solution to gain appropriate antimicrobial prescribing. Effective programs include selection of the most effective agents, specific dosages, frequency of administration, routes of administration, and duration of therapy. Additionally, a dual fluoroquinolone formulary, which typically incorporates one respiratory fluoroquinolone and ciprofloxacin, has been employed to increase the diversity of fluoroquinolone treatment and thus reduce the selective antimicrobial pressure. A combination of antimicrobial stewardship programs and a dual formulary option has been demonstrated to be a good approach to optimize the use of fluoroquinolones in the hospital. Two successful experiences in applying such strategies have been reported; in both cases the empiric fluoroquinolone prescribing was reduced.

Conclusion

Implementation of aggressive optimization strategies such as the combined use of antimicrobial stewardship programs and a dual fluoroquinolone formulary may maintain the efficacy of fluoroquinolones and preserve their utility for future patients.

Association between fluoroquinolone usage and a dramatic rise in ciprofloxacin-resistant Streptococcus pneumoniae in Canada, 1997-2006

This study evaluated the prevalence of fluoroquinolone usage and investigated the association between usage and resistance in respiratory isolates of Streptococcus pneumoniae in Canada. Fluoroquinolone susceptibility testing was conducted on S. pneumoniae collected from 25 medical centres across Canada over nine study years. Fluoroquinolone prescriptions and consumption figures were derived from data in the IMS Health, Canada CompuScript Audit. Between 1997 and 2006, 11825 S. pneumoniae isolates were collected. Ciprofloxacin resistance rates increased significantly (P<0.01) during the study from 0% to 4.5% in children (0-15 years), from 0.2% to 5.4% in adults (16-64 years) and from 1.4% to 11.6% in the elderly (> or = 65 years). Outpatient ciprofloxacin and respiratory fluoroquinolone prescriptions increased by 55.6% (38.2 prescriptions/1000 population to 59.4 prescriptions/1000 population; P<0.01) and 416.2% (5.3 prescriptions/1000 to 27.4 prescriptions/1000; P<0.01), respectively. Ciprofloxacin and respiratory fluoroquinolone consumption increased by 10.6% [1.1 defined daily doses (DDDs)/1000/day to 1.2 DDDs/1000/day; P=0.02] and 38.2% (0.5 to 0.7 DDDs/1000/day; P=0.02), respectively, from 2001 to 2006. A strong association between ciprofloxacin use and resistance (R(2)=0.89) was identified. Fluoroquinolone resistance in S. pneumoniae increased significantly in Canada from 1997 to 2006 in conjunction with increased ciprofloxacin and respiratory fluoroquinolone consumption. Ciprofloxacin usage appears to be the biggest driver of resistance; however, total fluoroquinolone usage is also important.

Genodiversity of resistant Pseudomonas aeruginosa isolates in relation to antimicrobial usage density and resistance rates in intensive care units

OBJECTIVE

To evaluate the assumption that resistance rates in intensive care units (ICUs) are markedly influenced by cross-transmission events in addition to high rates of antimicrobial usage.

METHODS

This was a prospective ICU- and laboratory-based surveillance study involving 35 German ICUs from 1999 through 2004. A total of 585 ciprofloxacin- or imipenem-resistant isolates of Pseudomonas aeruginosa were investigated together with resistance rate and unit-based antimicrobial usage density. Antimicrobial use was reported in terms of defined daily doses per 1,000 patient-days. All the strains were assigned to ICU-based genotypes. Genodiversity was calculated as the numbers of indistinguishable ICU-based genotypes found per isolates tested. Reduced ICU-based genodiversity was taken as an indirect measure of frequently occurring cross-transmission events.

RESULTS

The genodiversity of ciprofloxacin- and imipenem-resistant P. aeruginosa isolates was significantly lower (P <=, by Fisher exact test) in ICUs with high resistance rate and low antimicrobial usage density (genodiversity, 0.50 and 0.50, respectively) than in ICUs that featured low resistance rate in the presence of high antimicrobial usage density (genodiversity, 0.90 and 0.95, respectively). In ICUs with low genodiversity, there was a greater rise in resistance rate with increasing antimicrobial usage density, compared with that in ICUs with high diversity.

CONCLUSIONS

This study on resistant P. aeruginosa isolates supports the assumption that high resistance rate in the presence of low antimicrobial usage density results from more-frequent cross-transmission events. A greater rise in resistance rate with increasing antimicrobial usage density in ICUs with low genodiversity indicates that resistance rate in ICUs might be markedly determined by cross-transmission events other than antimicrobial usage.

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.

Effect of a program to reduce hospital ciprofloxacin use on nosocomial Pseudomonas aeruginosa susceptibility to quinolones and other antimicrobial agents

OBJECTIVE

We evaluated the effect of an antimicrobial management effort to decrease ciprofloxacin use on the antibiotic susceptibility of nosocomial Pseudomonas aeruginosa isolates.

DESIGN

Retrospective, observational study.

SETTING

Tertiary care teaching hospital with 731 beds.

METHODS

The study was conducted between January 1, 2001, and December 31, 2007. Linear regression analyses and Student t tests were used to determine significant changes in drug use among patients and antimicrobial susceptibility patterns among nosocomial P. aeruginosa isolates during the 84-month period.

RESULTS

Following implementation of a program to reduce oral and intravenous use of ciprofloxacin in 2005, there was a 56.6% reduction in ciprofloxacin use (P < .001). Significant reductions in the mean percentage of nosocomial P. aeruginosa isolates that were resistant to ciprofloxacin (from 45.0% to 35.2%; P < .002) and the mean incidence of ciprofloxacin resistance (from 0.77 to 0.67 isolates recovered per 1,000 patient-days; P = .03) were noted after implementation of this program. The total quantity of antipseudomonal antibiotics consumed decreased, but the use of certain antipseudomonal antibiotics (ie, cefepime and imipenem/meropenem) increased. Among nosocomial P. aeruginosa isolates, the prevalence of imipenem/meropenem resistance increased, whereas the prevalence of cefepime resistance did not. During the 84 months of the study, there was a significant association between ciprofloxacin use and the percentage of nosocomial P. aeruginosa isolates that were resistant to ciprofloxacin (rho = 0.47; P = .011), but there was no correlation between ciprofloxacin use and the incidence of ciprofloxacin resistance (rho = 0.21; P = .26).

CONCLUSIONS

Major reductions in ciprofloxacin use were associated with small but significant improvements in the rate of ciprofloxacin susceptibility among nosocomial P. aeruginosa isolates. The impact of the program on other antipseudomonal agents was variable.

The Utility of Fluoroquinolones in the Critically Ill

Fluoroquinolone antibiotics have been used for more than 40 years to treat a variety of infections from simple uncomplicated urinary tract infections to infections as severe as nosocomial-acquired pneumonia. Their availability both orally and intravenously, ease of dosing, favorable safety profile, and broad spectrum of activity have led to the pervasive use of these agents in both the community and institutions. Unfortunately, this widespread use has led to the development of resistance and subsequently, increased mortality. Resistance, specifically with Pseudomonas aeruginosa and Escherichia coli, as well as their association with the development of Clostridium difficile–associated diarrhea, has led many clinicians to question the use of fluoroquinolones in the critically ill. This article will review these issues related to the use of fluoroquinolones, in an effort to better define their role among institutionalized patients.

Variability in rates of use of antibacterials among 130 US hospitals and risk-adjustment models for interhospital comparison

OBJECTIVE

To describe variability in rates of antibacterial use in a large sample of US hospitals and to create risk-adjusted models for interhospital comparison.

METHODS

We retrospectively surveyed the use of 87 antibacterial agents on the basis of electronic claims data from 130 medical-surgical hospitals in the United States for the period August 2002 to July 2003; these records represented 1,798,084 adult inpatients. Hospitals were assigned randomly to the derivation data set (65 hospitals) or the validation data set (65 hospitals). Multivariable models predicting rates of antibacterial use were created using the derivation data set. These models were then used to predict rates of antibacterial use in the validation data set, which was compared with observed rates of antibacterial use. Rates of antibacterial use was measured in days of therapy per 1,000 patient-days.

RESULTS

Across the surveyed hospitals, a mean of 59.3% of patients received at least 1 dose of an antimicrobial agent during hospitalization (range for individual hospitals, 44.4%-73.6%). The mean total rate of antibacterial use was 789.8 days of therapy per 1,000 patient-days (range, 454.4-1,153.4). The best model for the total rate of antibacterial use explained 31% of the variance in rates of antibacterial use and included the number of hospital beds, the number of days in the intensive care unit per 1,000 patient-days, the number of surgeries per 1,000 discharges, and the number of cases of pneumonia, bacteremia, and urinary tract infection per 1,000 discharges. Five hospitals in the validation data set were identified as having outlier rates on the basis of observed antibacterial use greater than the upper bound of the 90% prediction interval for predicted antibacterial use in that hospital.

CONCLUSION

Most adult inpatients receive antimicrobial agents during their hospitalization, but there is substantial variability between hospitals in the volume of antibacterials used. Risk-adjusted models can explain a significant proportion of this variation and allow for comparisons between hospitals for benchmarking purposes.

The utility of hospital antibiograms as tools for guiding empiric therapy and tracking resistance. Insights from the Society of Infectious Diseases Pharmacists

Hospital antibiograms are commonly used to help guide empiric antimicrobial treatment and are an important component of detecting and monitoring trends in antimicrobial resistance. To serve these purposes, antibiograms must be constructed using standardized methods that allow inter- and intrahospital comparisons. Antibiograms that include surveillance cultures and duplicate bacterial isolates can overestimate rates of resistance. In 2002, the National Committee for Clinical Laboratory Standards (now known as the Clinical and Laboratory Standards Institute [CLSI]) published standards for constructing antibiograms. According to national surveys, many of the recommended elements of the CLSI document have not been fully adopted. In lieu of full compliance with CLSI standards, it is necessary that the methods used to construct antibiograms are clearly delineated. Antibiograms have several limitations, such as their inability to track emergence of resistance during therapy. The antibiogram can serve as a valuable tool in guiding antimicrobial therapy, but other patient factors, such as previous infection history and antibiotic use, also need to be considered. Additional data are needed for specialized applications of resistance analyses.

Relationship between rates of antimicrobial consumption and the incidence of antimicrobial resistance in Staphylococcus aureus and Pseudomonas aeruginosa isolates from 47 French hospitals

OBJECTIVE

To investigate relationships between rates of antimicrobial consumption and the incidence of antimicrobial resistance in Staphylococcus aureus and Pseudomonas aeruginosa isolates from hospitals.

METHODS

We conducted an observational study that used retrospective data from 2002 and linear regression to model relationships. Hospitals were asked to collect data on consecutive S. aureus and P. aeruginosa isolates, consumption rates for antibiotics (ie, anti-infectives for systemic use as defined by Anatomical Therapeutic Chemical class J01), and hospital characteristics, including infection control policies. Rates of methicillin resistance in S. aureus and rates of ceftazidime and ciprofloxacin resistance in P. aeruginosa were expressed as the percentage of isolates that were nonsusceptible (ie, either resistant or intermediately susceptible) and as the incidence of nonsuceptible isolates (ie, the number of nonsuceptible isolates recovered per 1,000 patient-days). The rate of antimicrobial consumption was expressed as the number of defined daily doses per 1,000 patient-days.

SETTING

Data were obtained from 47 French hospitals, and a total of 12,188 S. aureus isolates and 6,370 P. aeruginosa isolates were tested.

RESULTS

In the multivariate analysis, fewer antimicrobials showed a significant association between the consumption rate and the percentage of isolates that were resistant than an association between the consumption rate and the incidence of resistance. The overall rate of antibiotic consumption, not including the antibiotics used to treat methicillin-resistant S. aureus infection, explained 13% of the variance between hospitals in the incidence of methicillin resistance among S. aureus isolates. The incidence of methicillin resistance in S. aureus isolates increased with the use of ciprofloxacin and levofloxacin and with the percentage of the hospital's beds located in intensive care units (adjusted multivariate coefficient of determination [aR(2)], 0.30). For P. aeruginosa, the incidence of ceftazidime resistance was greater in hospitals with higher consumption rates for ceftazidime, levofloxacin, and gentamicin (aR(2), 0.37). The incidence of ciprofloxacin resistance increased with the use of fluoroquinolones and with the percentage of a hospital's beds located in intensive care ( aR(2), 0.28).

CONCLUSIONS

A statistically significant relationship existed between the rate of fluoroquinolone use and the rate of antimicrobial resistance among S. aureus and P. aeruginosa isolates. The incidence of resistant isolates showed a stronger association with the rate of antimicrobial use than did the percentage of isolates with resistance.

In vitro fluoroquinolone susceptibility ofPseudomonas aeruginosaisolates from dogs with ulcerative keratitis

OBJECTIVE

To determine the in vitro fluoroquinolone susceptibility profiles of Pseudomonas aeruginosa isolates from dogs with ulcerative keratitis. Animals-27 dogs with P. aeruginosa-associated ulcerative keratitis.

PROCEDURES

P. aeruginosa isolates from dogs with ulcerative keratitis were collected during a 3-year period. Isolates were tested by use of the disk diffusion method for their susceptibility to 7 fluoroquinolones that are available as commercial ophthalmic preparations. The antimicrobials included second- (ciprofloxacin, ofloxacin, norfloxacin, and lomefloxacin), third- (levofloxacin), and fourth-generation (gatifloxacin and moxifloxacin) fluoroquinolones. Isolates were designated as susceptible, intermediate, or resistant to the various antimicrobials. The percentage of susceptible isolates was compared among individual fluoroquinolones and among fluoroquinolone generations.

RESULTS

None of the dogs had received topical or systemic fluoroquinolone treatment prior to referral. Twenty-seven P. aeruginosa isolates were collected during the study period. In vitro, bacterial resistance to the tested fluoroquinolones was infrequently identified (24/ 27 isolates were susceptible to all fluoroquinolones evaluated); susceptibility percentages ranged from 88.9% to 100% for individual antimicrobials. There were no significant differences among isolate susceptibilities to the individual antimicrobials or among generations of fluoroquinolones.

CONCLUSIONS AND CLINICAL RELEVANCE

On the basis of these in vitro data, none of the 7 evaluated fluoroquinolones (individually or collectively by generation) appeared to offer a clinically important advantage in the treatment of P. aeruginosa-associated ulcerative keratitis in dogs. Among the P. aeruginosa isolates collected from dogs with ulcerative keratitis in this study, the likelihood of susceptibility to the fluoroquinolones evaluated was high.

Comparison of Outpatient Systemic Antibacterial Use in 2004 in the United States and 27 European Countries

The European Surveillance of Antimicrobial Consumption (ESAC) project collects data on antibacterial use in Europe, applying the Anatomic Therapeutic Chemical classification system and defined daily dose methodology, as recommended by the World Health Organization. Comparable data for the United States have been collected from IMS Health. The IMS Health sales data, processed according to ESAC methodology, suggest that outpatient antibacterial use in the United States is high (only 3 of 27 European countries used more) and is mainly characterized by a shift towards newer antibiotics.

Measurement of Adult Antibacterial Drug Use in 130 US Hospitals: Comparison of Defined Daily Dose and Days of Therapy

BACKGROUND

Hospitals are advised to measure antibiotic use and monitor its relationship to resistance. The World Health Organization's recommended metric is the defined daily dose (DDD). An alternative measure is the number of days of therapy (DOT). The purpose of this study was to contrast these measures.

METHODS

We measured the use of 50 antibacterial drugs that were administered to adults who were discharged from 130 US hospitals during 1 August 2002-31 July 2003.

RESULTS

Of 1,795,504 patients, 1,074,174 received at least 1 dose of an antibacterial drug (59.8%). The mean (+/- standard deviation) of total antibacterial drug use measured by the number of DDDs per 1000 patient-days and the number of DOTs per 1000 patient-days were not significantly different (792+/-147 and 776+/-120, respectively; P=.137), although the correlation was poor (r=0.603). For some individual drugs, such as levofloxacin and linezolid, there was no significant difference between DDDs per 1000 patient-days and DOTs per 1000 patient-days, because the administered daily dosage was nearly equivalent to the DDD. When the administered dosage exceeded the DDD, such as for ampicillin-sulbactam and cefepime, estimates of use based on DDDs per 1000 patient-days significantly exceeded those based on DOTs per 1000 patient-days (P<.001). When the administered dosage was less than the DDD, such as for piperacillin-tazobactam and ceftriaxone, estimates of use based on DDDs per 1000 patient-days were significantly lower than those based on DOTs per 1000 patient-days (P<.001).

CONCLUSION

The measurement of aggregate hospital antibiotic use by DDDs per 1000 patient-days and DOTs per 1000 patient-days is discordant for many frequently used antibacterial drugs, because the administered dose is dissimilar from the DDD recommended by the World Health Organization. DDD methods are useful for benchmarking purposes but cannot be used to make inferences about the number of DOTs or relative use for many antibacterial drugs.

Risk factors associated with resistance to ciprofloxacin in clinical bacterial isolates from intensive care unit patients

OBJECTIVE

To determine risk factors and outcomes associated with ciprofloxacin resistance in clinical bacterial isolates from intensive care unit (ICU) patients.

DESIGN

Prospective cohort study.

SETTING

Twenty-bed medical-surgical ICU in a Canadian tertiary care teaching hospital.

PATIENTS

All patients admitted to the ICU with a stay of at least 72 hours between January 1 and December 31, 2003.

METHODS

Prospective surveillance to determine patient comorbidities, use of medical devices, nosocomial infections, use of antimicrobials, and outcomes. Characteristics of patients with a ciprofloxacin-resistant gram-negative bacterial organism were compared with characteristics of patients without these pathogens.

RESULTS

Ciprofloxacin-resistant organisms were recovered from 20 (6%) of 338 ICU patients, representing 38 (21%) of 178 nonduplicate isolates of gram-negative bacilli. Forty-nine percent of Pseudomonas aeruginosa isolates and 29% of Escherichia coli isolates were resistant to ciprofloxacin. In a multivariate analysis, independent risk factors associated with the recovery of a ciprofloxacin-resistant organism included duration of prior treatment with ciprofloxacin (relative risk [RR], 1.15 per day [95% confidence interval {CI}, 1.08-1.23]; P<.001), duration of prior treatment with levofloxacin (RR, 1.39 per day [95% CI, 1.01-1.91]; P=.04), and length of hospital stay prior to ICU admission (RR, 1.02 per day [95% CI, 1.01-1.03]; P=.005). Neither ICU mortality (15% of patients with a ciprofloxacin-resistant isolate vs 23% of patients with a ciprofloxacin-susceptible isolate; P=.58) nor in-hospital mortality (30% vs 34%; P=.81) were statistically significantly associated with ciprofloxacin resistance.

CONCLUSIONS

ICU patients are at risk of developing infections due to ciprofloxacin-resistant organisms. Variables associated with ciprofloxacin resistance include prior use of fluoroquinolones and duration of hospitalization prior to ICU admission. Recognition of these risk factors may influence antibiotic treatment decisions.

Using interrupted time series analysis to assess associations of fluoroquinolone formulary changes with susceptibility of gram-negative pathogens and isolation rates of methicillin-resistant Staphylococcus aureus

The use of fluoroquinolones has been linked to increasing bacterial resistance and infection and/or colonization with already resistant pathogens both as a risk factor and based on volume of use. Changes in individual fluoroquinolones used in an institution may also be related to these clinical problems. Interrupted time series analysis, which allows for assessment of the associations of an outcome attributable to a specific event in time, was used to study the effect of changes in our hospital's fluoroquinolone formulary on fluoroquinolone susceptibility rates in select gram-negative pathogens and the methicillin-resistant Staphylococcus aureus (MRSA) isolation rate. Susceptibility rates to ciprofloxacin were considered for the period of 1993 through 2004, while the MRSA isolation rate was assessed from 1995 through 2004. Levofloxacin was added to the formulary in 1999, and gatifloxacin was substituted for levofloxacin in 2001. Statistically significant changes in the already declining rates of susceptibility of Pseudomonas aeruginosa (P, 0.042) and Escherichia coli (P, 0.004) to ciprofloxacin and in the already rising MRSA isolation rate (P, 0.001) were associated with the addition of levofloxacin to the formulary. Substitution of gatifloxacin for levofloxacin on the formulary was associated with reversals in the downward trend in E. coli susceptibility to ciprofloxacin and the upward trend in MRSA isolation rate. No associations were detected on susceptibility of Klebsiella pneumoniae or Proteus mirabilis to ciprofloxacin. These findings suggest that potential changes in susceptibility to fluoroquinolones and isolation of MRSA may vary by both drug and organism.

Differential effects of levofloxacin and ciprofloxacin on the risk for isolation of quinolone-resistant Pseudomonas aeruginosa

Due to the greater in vitro activity of ciprofloxacin than that of levofloxacin against Pseudomonas aeruginosa, the likelihood of isolating a clinical strain of quinolone-resistant (QR) P. aeruginosa might be greater after exposure to levofloxacin than ciprofloxacin. We examined the risk of isolating QR P. aeruginosa in association with prior levofloxacin or ciprofloxacin exposure. A case-case-control study was conducted. Two groups of cases, one with nosocomial QR P. aeruginosa infections and one with nosocomial quinolone-susceptible (QS) P. aeruginosa infections, were compared to a control group of hospitalized patients without P. aeruginosa infections. Bivariable and multivariable analyses were used to determine risk factors for isolation of QR P. aeruginosa and QS P. aeruginosa. One hundred seventeen QR P. aeruginosa and 255 QS P. aeruginosa cases were identified, and 739 controls were selected. Exposures to ciprofloxacin were similar among all three groups (8% for controls, 9.4% for QR P. aeruginosa cases, and 7.5% for QS P. aeruginosa cases; P >/= 0.6). Levofloxacin use was more frequent in the QR P. aeruginosa cases than in the controls (35.9% and 22.1%, respectively; odds ratio [OR] = 2.0; 95% confidence interval [CI] = 1.3 to 3.0) and less frequent in QS P. aeruginosa cases (14.1% of QS P. aeruginosa cases; OR = 0.6; 95% CI = 0.4 to 0.9). In multivariable analysis, levofloxacin, but not ciprofloxacin, was a significant risk factor for isolation of QR P. aeruginosa (OR for levofloxacin = 1.7 [95% CI = 1.0 to 2.9]; OR for ciprofloxacin = 1.2 [95% CI = 0.6 to 2.5]). Levofloxacin was associated with a reduced risk of isolation of QS P. aeruginosa (OR = 0.6; 95% CI = 0.4 to 0.9), whereas ciprofloxacin had no significant effect (OR = 1.0; 95% CI = 0.6 to 1.8). In conclusion, the use of levofloxacin, but not ciprofloxacin, was associated with isolation of QR P. aeruginosa.

Fluoroquinolone-resistant Pseudomonas aeruginosa: assessment of risk factors and clinical impact

PURPOSE

Pseudomonas aeruginosa infections have been associated with considerable morbidity and mortality. Fluoroquinolones (FQ) are the only oral therapy available for P. aeruginosa infections, but resistance is increasingly prevalent.

METHODS

We examined annual trends in FQ-resistant P. aeruginosa (FQRPA) from 1991 to 2000. Subsequently, inpatients with a clinical culture positive for P. aeruginosa between January 1, 1999 and December 31, 2000 were included in a case control study to identify risk factors for FQ resistance and a cohort study to examine the impact of FQ resistance on outcomes in P. aeruginosa.

RESULTS

Annual prevalence of FQRPA increased from 15% in 1991 to 41% in 2000 (P <0.001 trend). Between 1999 and 2000, 332 P. aeruginosa isolates were FQ resistant and 540 were FQ susceptible. Prior FQ use was the only independent risk factor for FQRPA (adjusted OR = 3.43; 95% confidence interval [CI] 2.37, 4.96). Subjects with FQRPA had greater median hospital charges (62,325 dollars vs 48,734 dollars) (P =.007) and higher mortality (47.5% vs 35.5%) (P =.004). However, in a multivariate model, only imipenem resistance of the isolate was significantly associated with mortality. FQ resistance was not an independent risk factor.

CONCLUSIONS

FQRPA has increased significantly and is associated with prior FQ use. Limiting FQ use may curb the emergence of resistance among P. aeruginosa. FQRPA is associated with increased hospital charges, but other resistance patterns may have a more significant impact on mortality.

Antimicrobial drug utilisation in Dunedin Hospital, New Zealand, and its association with antimicrobial resistance

INTRODUCTION

Antimicrobial resistance (AR) to a drug can be considered a natural response to the selection pressure of that drug, with over prescribing being one of the major causes. Few investigations have evaluated the relationships between antimicrobial drug use in a hospital and antimicrobial resistance.

METHOD AND MATERIALS

Antimicrobial drug utilisation (AU) data were collated for Dunedin Hospital, New Zealand, and expressed as defined daily doses per 1000 patient days according to the World Health Organization's definition. The drug groups studied were glycopeptides, carbapenems, third and fourth generation cephalosporins and fluoroquinolones. Antibiograms were also analysed and possible associations between antimicrobial utilisation and resistance were investigated. The reduction of antimicrobial utilisation has also been explored by various means.

RESULTS

The utilisation of fluoroquinolones at Dunedin Hospital was high compared with hospitals in South Australia, increasing from 1999 to 2003 then decreasing in 2004 and 2005. The Spearman rank correlation coefficients for the associations between fluoroquinolone utilisation and resistance to ciprofloxacin were: rs = 0.79, p = 0.06 for Pseudomonas aeruginosa and rs = -0.37, p = 0.5 for Escherichia coli.

CONCLUSION

The findings of antimicrobial drug utilisation studies in hospital can serve to describe the pattern of drug use in the institution, to detect areas of concern, and to evaluate the impact of interventions taken to influence the use of drugs, especially when this use is associated with increasing antimicrobial drug resistance.

Five years of nosocomial Gram-negative bacteremia in a general intensive care unit: epidemiology, antimicrobial susceptibility patterns, and outcomes

OBJECTIVES

Nosocomial Gram-negative bacteremia in the critically ill is associated with significant morbidity and mortality. This study provides epidemiological and antimicrobial susceptibility data for nosocomial Gram-negative bacteremia in a general intensive care unit (ICU) over a five-year period.

METHODS

Positive blood cultures from January 1, 1999 to December 31, 2003 were reviewed for microbial etiology and susceptibilities. Patient charts were reviewed to determine the source of infection and outcome.

RESULTS

Forty-five nosocomial Gram-negative bacteremias occurred in 44 patients. Infection rates of 6.9/1000 admissions and 11.3/10,000 patient days remained stable. Admitting diagnoses included respiratory failure, solid organ transplant, post-surgery, and multi-trauma. Seven bacterial species were identified; Pseudomonas aeruginosa and Enterobacter spp were most common. Sources of bacteremia included pneumonia (48.9%), and central venous catheterization (22.2%). Antimicrobial susceptibilities were highest for imipenem, gentamicin, tobramycin, ceftazidime, and piperacillin-tazobactam. Ciprofloxacin susceptibility was inferior to imipenem, gentamicin, and tobramycin (p < 0.05). Mortality rates were 53.3% in the ICU, and 60% for overall hospitalization. Average length of ICU stay was 50.5 days compared to 6.13 days for all-comers.

CONCLUSIONS

Nosocomial Gram-negative bacteremia is associated with marked morbidity and mortality in critically ill patients. Significant resistance to ciprofloxacin was demonstrated. Empiric treatment regimens should be based on unit-specific data.

Optimal pharmacological therapy for community-acquired pneumonia: the role of dual antibacterial therapy

The optimal pharmacological therapy of community-acquired pneumonia (CAP) is one of the most ardently debated issues in medicine. Presently, most guidelines recommend either a fluoroquinolone alone or dual therapy with a third-generation cephalosporin plus a macrolide in patients hospitalised with CAP, but few provide clinicians with specific considerations for selecting from these agents. Despite a similar spectrum of activity and favourable resistance patterns (for fluoroquinolones and third-generation cephalosporins) against CAP pathogens, there is emerging evidence that dual therapy may be superior to monotherapy in certain populations.In patients with non-severe CAP, the evidence supports the use of either monotherapy or dual therapy in most patients; however, patients with severe CAP or bacteraemic pneumococcal CAP experience improved survival when treated with dual therapy. It is unclear from this evidence if any specific combination of agents is the most effective, but the combination of a third-generation cephalosporin plus a macrolide is the most extensively studied. Dual therapy was superior to monotherapy irrespective of the susceptibility of the aetiological pathogen, thus insufficient antimicrobial spectrum does not explain the disparity. The most likely explanation for improved outcomes with dual therapy is the combined effect of optimised antimicrobial spectrum (including atypicals), decreased impact of resistance to a single agent and the immunomodulatory effects of macrolides. Increasing resistance in patients with non-severe CAP warrants the consideration of dual therapy and perhaps a reappraisal of agents usually reserved for second-line therapy, including doxycycline, in these populations as well. In light of the available evidence, dual therapy should be strongly considered in all patients with severe CAP, especially when complicated by pneumococcal bacteraemia.

Antimicrobial stewardship programs in health care systems

Antimicrobial stewardship programs in hospitals seek to optimize antimicrobial prescribing in order to improve individual patient care as well as reduce hospital costs and slow the spread of antimicrobial resistance. With antimicrobial resistance on the rise worldwide and few new agents in development, antimicrobial stewardship programs are more important than ever in ensuring the continued efficacy of available antimicrobials. The design of antimicrobial management programs should be based on the best current understanding of the relationship between antimicrobial use and resistance. Such programs should be administered by multidisciplinary teams composed of infectious diseases physicians, clinical pharmacists, clinical microbiologists, and infection control practitioners and should be actively supported by hospital administrators. Strategies for changing antimicrobial prescribing behavior include education of prescribers regarding proper antimicrobial usage, creation of an antimicrobial formulary with restricted prescribing of targeted agents, and review of antimicrobial prescribing with feedback to prescribers. Clinical computer systems can aid in the implementation of each of these strategies, especially as expert systems able to provide patient-specific data and suggestions at the point of care. Antibiotic rotation strategies control the prescribing process by scheduled changes of antimicrobial classes used for empirical therapy. When instituting an antimicrobial stewardship program, a hospital should tailor its choice of strategies to its needs and available resources.

Microbiological rationale for the utilisation of prulifloxacin, a new fluoroquinolone, in the eradication of serious infections caused by Pseudomonas aeruginosa

Minimal inhibitory concentrations (MICs) of prulifloxacin were evaluated in comparison with ciprofloxacin, levofloxacin and moxifloxacin against a large collection (N = 300) of Pseudomonas aeruginosa strains characterised according to the CLSI/NCCLS microdilution method. Additional in vitro tests (time-kill curves and mutant prevention concentration (MPC) determinations) were carried out. Assuming a susceptibility breakpoint for prulifloxacin identical to that of ciprofloxacin, the new fluoroquinolone emerged as the most potent antibiotic (72% of susceptible strains versus 65%, 61% and 23% for ciprofloxacin, levofloxacin and moxifloxacin, respectively). Time-kill tests at 4x MIC confirmed the pronounced bactericidal potency of the drug against P. aeruginosa. Amongst the members of the fluoroquinolone class assessed, prulifloxacin produced the lowest MPC values (< or = 4 mg/L). Our in vitro results indicate that prulifloxacin represents the most powerful antipseudomonal drug available today.

Pseudomonas aeruginosa, Staphylococcus aureus, and fluoroquinolone use

Increasingly resistant bacteria in sickle cell disease patients indicate need to evaluate extendedspectrum cephalosporin therapy.

Few long-term multicenter investigations have evaluated the relationships between aggregate antimicrobial drug use in hospitals and bacterial resistance. We measured fluoroquinolone use from 1999 through 2003 in a network of US hospitals. The percentages of fluoroquinolone-resistant Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) were obtained from yearly antibiograms at each hospital. Univariate linear regression showed significant associations between a hospital's volume of fluoroquinolone use and percent resistance in most individual study years (1999–2001 for P. aeruginosa, 1999–2002 for S. aureus). When the method of generalized estimating equations was used, a population-averaged longitudinal model incorporating total fluoroquinolone use and the previous year's resistance (to account for autocorrelation) did not show a significant effect of fluoroquinolone use on percent resistance for most drug-organism combinations, except for the relationship between levofloxacin use and percent MRSA. The ecologic relationship between fluoroquinolone use and resistance is complex and requires further study.

Quinolones in 2005: an update

Quinolones are one of the largest classes of antimicrobial agents used worldwide. This review considers the quinolones that are available currently and used widely in Europe (norfoxacin, ciprofloxacin, ofloxacin, levofloxacin and moxifloxacin) within their historical perspective, while trying to position them in the context of recent and possible future advances based on an understanding of: (1) their chemical structures and how these impact on activity and toxicity; (2) resistance mechanisms (mutations in target genes, efflux pumps); (3) their pharmacodynamic properties (AUC/MIC and Cmax/MIC ratios; mutant prevention concentration and mutant selection window); and (4) epidemiological considerations (risk of emergence of resistance, clonal spread). Their main indications are examined in relation to their advantages and drawbacks. Overall, it is concluded that these important agents should be used in an educated fashion, based on a careful balance between their ease of use and efficacy vs. the risk of emerging resistance and toxicity. However, there is now substantial evidence to support use of the most potent drug at the appropriate dose whenever this is required.

Hospital and Community Fluoroquinolone Use and Resistance in Staphylococcus aureus and Escherichia coli in 17 US Hospitals

BACKGROUND

Fluoroquinolones are widely prescribed in hospitals and the community. Previous studies have shown associations between fluoroquinolone use and isolation of fluoroquinolone-resistant Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA). We performed an ecologic-level study to determine whether variability in hospital percentages of fluoroquinolone-resistant E. coli and MRSA were associated with fluoroquinolone use in hospitals and their surrounding communities.

METHODS

We measured fluoroquinolone use in 17 US hospitals and their surrounding communities in the year 2000. Data on fluoroquinolone use in hospitals was electronically extracted from billing data. Data on fluoroquinolone use in communities was obtained from IMS health data for all prescriptions filled in pharmacies within a 16-km radius of each hospital. We used hospital antibiograms to determine the percentage of isolates that were fluoroquinolone-resistant E. coli and MRSA, and we performed linear regression to determine the relationship between percentage of resistant isolates and fluoroquinolone use in hospitals and their surrounding communities.

RESULTS

There was a significant association between total fluoroquinolone use within hospitals and percentage of S. aureus isolates that were MRSA (r=0.77; P=.0003) and between total fluoroquinolone use in the community and percentage of E. coli isolates that were fluoroquinolone-resistant E. coli (r=0.68; P=.003). Population density within the 16-km radius also correlated with MRSA percentage (r=0.57; P=.015) and fluoroquinolone-resistant E. coli percentage (r=0.85; P=.002), but associations between total fluoroquinolone use and resistance remained significant after adjustment for population density.

CONCLUSIONS

In this ecologic analysis, we found associations between fluoroquinolone use in hospitals and methicillin resistance in S. aureus and between fluoroquinolone use in communities and fluoroquinolone resistance in E. coli in hospitals. Antimicrobial use in hospitals and communities may have different relative importance with regard to resistance in different pathogens encountered in hospitals.

Hospital-Level Rates of Fluoroquinolone Use and the Risk of Hospital-Acquired Infection with Ciprofloxacin-Nonsusceptible Pseudomonas aeruginosa

BACKGROUND

In recent years, Pseudomonas aeruginosa has become increasingly resistant to fluoroquinolones, and fluoroquinolone use in the United States has also increased. Our objective was to determine whether higher hospital-level rates of use of ciprofloxacin, levofloxacin, and moxifloxacin antimicrobials were predictors that a higher proportion of P. aeruginosa isolates from hospital-acquired infections (hereafter, "hospital-acquired isolates") would be nonsusceptible to ciprofloxacin.

METHODS

We identified all hospital-acquired isolates from 14 hospitals in the Northern California Kaiser Permanente health care delivery system between 1998 and 2003 and determined their susceptibility to ciprofloxacin. For each facility, we determined the number of days of fluoroquinolone use per 1000 patient-days, by calendar quarter. We used a logistic regression model to analyze the data, with susceptibility status as the outcome variable. Hospital-level rates of use of the 3 fluoroquinolones were the predictors of interest; we adjusted for year, for use of nonquinolone antimicrobials, and for patient variables, including the number of days spent in the hospital in the prior year and fluoroquinolone use in the prior year. The model tested whether isolates from those facilities with higher rates of use of antimicrobials were more likely to be nonsusceptible to ciprofloxacin.

RESULTS

Of 6099 isolates tested, 15% were not susceptible to ciprofloxacin. The nonsusceptibility rate increased from 9% to 20% between 1998 and 2003. Both the overall rate of use at the hospital and prior patient-specific use of ciprofloxacin, levofloxacin, and moxifloxacin were found to be independent predictors that a subsequent P. aeruginosa isolate would be nonsusceptible to ciprofloxacin.

CONCLUSIONS

Higher hospital-level rates of use of ciprofloxacin, levofloxacin, and moxifloxacin are each associated with an increased proportion of hospital-acquired P. aeruginosa isolates being nonsusceptible to ciprofloxacin.

Defining the need for new antimicrobials: clinical and economic implications of resistance in the hospitalised patient

Resistance among pathogens causing the most common infections encountered in hospitalised patients is increasing. Due to this resistance, the clinical efficacy of current antimicrobial agents is decreasing against many pathogens, including Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, Pseudomonas aeruginosa, extended-spectrum beta-lactamases, and AmpC beta-lactamase-producing organisms. Studies assessing the impact of these resistance mechanisms on clinical outcomes have been performed; however, studies determining the economic impact of resistance have been limited. Strategies to retain the clinical efficacy of currently available agents include the initiation of antimicrobials with efficacy against the suspected pathogen(s) based on data obtained from local antibiograms, the use of combination therapy, and pharmacodynamic optimisation. Once a broad-spectrum regimen has been initiated, de-escalation to narrow, targeted antimicrobial therapy based on susceptibility data is warranted. Despite these efforts, new antimicrobials with novel mechanisms of action are eagerly anticipated to extend the current armamentarium against the growing population of multi-drug-resistant pathogens.

Infection Control in Intensive Care Units

For patients in intensive care units, the development of an infection is associated with an increase in morbidity, mortality, and cost. These infections are largely preventable through the implementation of infection control programs. Infection control programs must focus on 3 general strategies: (1) prevention of health care-associated infections, (2) containment of pathogens that pose a health risk and/or are resistant to routine antibiotics, and (3) development of strategies to limit the emergence of resistant microorganisms through optimal and appropriate antimicrobial utilization. The purpose of this article is to review these 3 general strategies.

Fluoroquinolone-resistant Pseudomonas aeruginosa: risk factors for acquisition and impact on outcomes

OBJECTIVES

Resistance among Pseudomonas aeruginosa has risen dramatically and parallels the increase in fluoroquinolone (FQ) prescribing in recent years. Risk factors for FQ resistance in P. aeruginosa and its impact on outcomes need to be well characterized.

METHODS

A case-control study was carried out on hospitalized adult patients from whom FQ-resistant (case) and FQ-susceptible (control) P. aeruginosa were isolated.

RESULTS

A total of 177 patients with positive cultures (91 cases and 86 controls) and 119 with documented infections (65 cases, 54 controls) were included in risk factor and outcomes analysis, respectively. Independent risk factors for FQ resistance were: FQ exposure (OR 12.6, CI 4.95-32), nosocomial acquisition (OR 8.6, CI 3.5-20.7), and diabetes mellitus (OR 6.4, CI 2.1-19.3). An FQ agent was prescribed in 59% of patients receiving an 'antipseudomonal' empirical regimen. Compared with controls, FQ-resistant cases had a median delay to receiving effective therapy of 3.5 days versus 1 day and poorer outcomes: (i) lower complete response rate (45% versus 63%, P=0.04); (ii) longer time to achieve clinical stability (8 days versus 3 days, P=0.005); and (iii) higher infection-related mortality (21% versus 7%; OR = 2.9, 0.9-9.4). Empirical FQ use (OR 4.6, CI 1.5-14.3), FQ resistance (OR 3.6, CI 1.0-13.1), and high APACHE II score (OR 1.1, CI 1.0-1.2) were independent risk factors for increased mortality.

CONCLUSIONS

FQ exposure from widespread prescribing is a modifiable risk factor for FQ resistance in P. aeruginosa. FQ empirical therapy for Pseudomonas infections may be associated with significant delays in administering effective therapy resulting in adverse outcomes.