Methicillin-resistant Staphylococcus aureus and antimicrobial use in Belgian hospitals

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.

Is Methicillin Resistance Associated with a Worse Prognosis in Staphylococcus aureus Ventilator-Associated Pneumonia?

BACKGROUND

Excess mortality associated with methicillin resistance in patients with Staphylococcus aureus ventilator-associated pneumonia (SA-VAP), taking into account such confounders as treatment adequacy and time in the intensive care unit (ICU), have not been adequately estimated.

METHODS

One hundred thirty-four episodes of SA-VAP entered in the Outcomerea database were studied. Patients from whom methicillin-resistant S. aureus (MRSA) was recovered were compared with those from whom methicillin-susceptible S. aureus (MSSA) was recovered, stratified for duration of stay in the ICU at the time of VAP diagnosis and adjusted for confounders (severity at admission, characteristics at VAP diagnosis, and treatment adequacy).

RESULTS

Treatment was adequate within 24 h after VAP diagnosis for 86% of the 65 MSSA-infected patients and 77% of the 69 MRSA-infected patients (P = .2). Polymicrobial VAP was more commonly associated with MSSA than with MRSA (49.2% vs. 25.7%; P = .01). MRSA infection was associated with a lower prevalence of coma at hospital admission and a higher rate of use of central venous lines and fluoroquinolones during the first 48 h of the ICU stay. The rates of shock, recurrence, and superinfection were similar in both groups. The crude hospital mortality rate was higher for MRSA-infected patients than for MSSA-infected patients (59.4% vs. 40%; P = .024). This difference disappeared after controlling for time in the ICU before VAP and parameters imbalanced at ICU admission (odds ratio [OR], 1.23; 95% confidence interval [CI], 0.49-3.12; P = .7) and remained unchanged after further adjustments for initial treatment adequacy and polymicrobial VAP (OR, 0.98; 95% CI, 0.36-2.66).

CONCLUSIONS

Differences in patient characteristics, initial ICU treatment, and time in the ICU confounded estimates of excess death due to MRSA VAP. After careful adjustment, methicillin resistance did not affect ICU or hospital mortality rates.

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.

[Impact of fluoroquinolone use on multidrug-resistant bacteria emergence]

During the last two decades, fluoroquinolone use has significantly increased in Europe and in the USA. This could be explained by the arrival of newer fluoroquinolones with antipneumoccal activity. Increased use of fluoroquinolones is associated with higher rates of bacterial resistance to these antibiotics. Resistance of Gram-negative bacilli to fluoroquinolones is increasing in industrialized countries. In addition, fluoroquinolone use has been identified as a risk factor for colonization and infection to methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumanni, extending-spectrum beta-lactamase producing Gram negative bacilli, and multidrug-resistant bacteria. Nosocomial infections due to multidrug-resistant bacteria are associated with higher mortality and morbidity rates. This could be related to more frequent inappropriate initial antibiotic treatment in these patients. Limiting the use of fluoroquinolones, limiting the duration of treatment with fluoroquinolones, and using appropriate dosage of these antibiotics could be suggested to reduce resistance to these antibiotics and to reduce the emergence of multidrug-resistant bacteria.

Nosocomial infections due to methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci at a university hospital in Taiwan from 1991 to 2003: resistance trends, antibiotic usage and in vitro activities of newer antimicrobial agents

A rapid increase of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infection (from 39% in 1991 to 75% in 2003) and vancomycin-resistant enterococci (VRE) (from 1.2% in 1996 to 6.1% in 2003) at a university hospital in Taiwan was found. The noticeable rise of MRSA and VRE was significantly correlated with the increased consumption of glycopeptides, β-lactam–β-lactamase inhibitor combinations, extended-spectrum cephalosporins, carbapenems and fluoroquinolones (Pearson's correlation coefficient, P < 0.05). Minimum inhibitory concentrations (MICs) of 100 non-duplicate blood isolates of MRSA (in 2003) and of 25 non-duplicate isolates of vancomycin-resistant Enterococcus faecalis and 172 vancomycin-resistant Enterococcus faecium (in 1996–2003) causing nosocomial infection recovered from various clinical specimens of patients treated at the hospital to nine antimicrobial agents were determined by the agar dilution method. All of these isolates were susceptible to linezolid and were inhibited by 0.5 mg/L of tigecycline, and all MRSA isolates were inhibited by daptomycin 1 mg/L, including two isolates of MRSA with heteroresistance to vancomycin. Daptomycin had two-fold better activity against vancomycin-resistant E. faecalis (MIC₉₀, 2 mg/L) than against vancomycin-resistant E. faecium (MIC₉₀, 4 mg/L). Decreased susceptibilities of vancomycin-resistant E. faecium and MRSA to quinupristin/dalfopristin (non-susceptibility 25% and 8%, respectively) were found. Telithromycin had poor activity against the isolates tested (MIC₉₀, 8 mg/L). Linezolid, daptomycin and tigecycline may represent therapeutic options for infections caused by these resistant Gram-positive organisms.

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.

Methicillin-resistant Staphylococcus aureus in horses and horse personnel, 2000-2002

Methicillin-resistant Staphylococcus aureus was isolated from horses and horse personnel in a pattern suggestive of interspecies transmission of a human-origin clone.

Methicillin-resistant Staphylococcus aureus (MRSA) infection was identified in 2 horses treated at a veterinary hospital in 2000, prompting a study of colonization rates of horses and associated persons. Seventy-nine horses and 27 persons colonized or infected with MRSA were identified from October 2000 to November 2002; most isolations occurred in a 3-month period in 2002. Twenty-seven (34%) of the equine isolates were from the veterinary hospital, while 41 (51%) were from 1 thoroughbred farm in Ontario. Seventeen (63%) of 27 human isolates were from the veterinary hospital, and 8 (30%) were from the thoroughbred farm. Thirteen (16%) horses and 1 (4%) person were clinically infected. Ninety-six percent of equine and 93% of human isolates were subtypes of Canadian epidemic MRSA-5, spa type 7 and possessed SCCmecIV. All tested isolates from clinical infections were negative for the Panton-Valentine leukocidin genes. Equine MRSA infection may be an important emerging zoonotic and veterinary disease.

Antibiotic prescribing as a risk factor for MRSA

There is accumulating evidence to support the role of specific antibiotic classes as risk factors for selecting meticillin-resistant Staphylococcus aureus (MRSA). Crucially, however, controlled studies of antimicrobial prescribing interventions are lacking. The evidence for the association between antimicrobial prescribing and expansion of MRSA is reviewed here.

First-generation fluoroquinolone use and subsequent emergence of multiple drug-resistant bacteria in the intensive care unit

OBJECTIVE

The objective of this study was to determine the relationship between fluoroquinolone (FQ) use and subsequent emergence of multiple drug-resistant bacteria (MRB) in the intensive care unit (ICU).

DESIGN

The authors conducted a prospective observational cohort study and a case control study.

SETTING

The study was conducted in a 30-bed ICU.

METHODS

All immunocompetent patients hospitalized for >48 hrs who did not receive antibiotics before ICU admission were eligible during a 15-month period. Routine MRB screening was performed at ICU admission and weekly thereafter. This screening included tracheal aspirate and nasal, anal, and axilla swabs. Univariate and multivariate analyses were used to determine risk factors for MRB emergence in the ICU. In addition, a case control study was performed to determine whether FQ use is associated with subsequent emergence of MRB.

RESULTS

Two hundred thirty-nine patients were included; 108 ICU-acquired MRB were isolated in 77 patients. FQ use and longer duration of antibiotic treatment were identified as independent risk factors for MRB occurrence (odds ratio [95% confidence interval [CI] = 3.3 [1.7-6.5], 1.1 [1.0-1.2]; p < .001; respectively). One hundred thirty-five (56%) patients received FQ; matching was successful for 72 (53%) of them. Number of MRB (40 vs. 15 per 1,000 ICU days; p = .019) and percentage of patients with MRB (40% vs. 22%; OR [95% CI] = 1.5 [1.0-2.4]; p = .028) were significantly higher in cases than in controls. Although methicillin-resistant Staphylococcus aureus (26% vs. 12%; OR [95% CI] = 1.6 [.6-2.9]; p = .028) and extending-spectrum beta-lactamase-producing Gram-negative bacilli (11% vs. 1%; OR [95% CI] = 4.7 [0.7-30.2]; p = .017) rates were higher in cases than in controls, ceftazidime or imipenem-resistant Pseudomonas aeruginosa (15% vs. 8%), Acinetobacter baumannii (1% vs. 5%), and Stenotrophomonas maltophilia (2% vs. 1%) rates were similar (p > .05) in case and control patients.

CONCLUSION

FQ use and longer duration of antibiotic treatment are independently associated with MRB emergence. Reducing antimicrobial treatment duration and restricting FQ use could be suggested to control MRB spread in the ICU.

Risk factors for acquisition of methicillin-resistant Staphylococcus aureus (MRSA) by patients with cystic fibrosis

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasing problem for patients with cystic fibrosis (CF). It has been associated with clinical deterioration in some patients with CF, creates additional infection control problems, and may affect acceptance onto transplant waiting lists. Recent attempts to eradicate the organism have met with only moderate success. An understanding of those factors which increase the risk of acquisition of MRSA by CF patients will aid the development of effective preventative strategies. We conducted a retrospective case-control study comparing a variety of risk factors for 15 MRSA-positive patients and 30 age-sex-matched MRSA-negative controls who attended the Regional Paediatric or Regional Adult Cystic Fibrosis Units in Leeds. During the year prior to initial isolation, MRSA-positive CF patients spent more days in hospital (mean 19.8 days versus 5.5 days, p=0.0003), received more treatment days of oral ciprofloxacin (43.5 days versus 13.9 days, p=0.03) more treatment days of oral/intravenous cephalosporins (42.7 days versus 15.4 days, p=0.04) and were more likely to be chronically infected with Aspergillus fumigatus (40% versus 10%, p=0.04) than the age-sex-matched MRSA-negative controls. There were no significant differences in observed clinical parameters (clinical and X-ray scores) with between the two groups. Minimising the number and length of hospital admissions and judicious use of antibiotics, particularly ciprofloxacin, should be the key components of any strategies designed to reduce the risk of MRSA acquisition by patients with CF.

Antimicrobial drug use and methicillin-resistant Staphylococcus aureus, Aberdeen, 1996-2000

Relationships between antimicrobial use and MRSA prevalence are analyzed in Aberdeen, Scotland.

Similar to many hospitals worldwide, Aberdeen Royal Infirmary has had an outbreak of methicillin-resistant Staphylococcus aureus (MRSA). In this setting, the outbreak is attributable to two major clones. The relationships between antimicrobial use and MRSA prevalence were analyzed by time-series analysis. From June 1997 to December 2000, dynamic, temporal relationships were found between monthly %MRSA and previous %MRSA, macrolide use, third-generation cephalosporin use, and fluoroquinolone use. This study suggests that use of antimicrobial drugs to which the MRSA outbreak strains are resistant may be an important factor in perpetuating the outbreak. Moreover, this study confirmed the ecologic effect of antimicrobial drug use (i.e., current antimicrobial use) may have an effect on resistance in future patients. Although these results may not be generalized to other hospitals, they suggest new directions for control of MRSA, which has thus far proved difficult and expensive.

Use of antibiotics in hospitals in south-western France

Data on the use of antibiotics were collected by means of a questionnaire from 49 hospitals in south-western France. Use was expressed as a usage density rate: number of defined daily doses (DDDs) per 1000 patient-days. The average use of antibiotics amounted to 402 DDDs per 1000 patient-days and varied between 60 and 734. In acute-care wards, the amount of antibiotic use increased with the size of the hospital: 461 DDDs per 1000 patient-days for group A (<100 beds), 510 DDDs per 1000 patient-days for group B (more than 100 and less then 300 beds) and 676 DDDs per 1000 patient-days for group C (>300 beds). The rate of use differed among different types of hospital areas and varied from 58 for psychiatry departments to more than 1273 DDDs per 1000 patient-days for the infectious diseases departments. Broad-spectrum penicillins were the most frequently prescribed antibiotics. Fluoroquinolone and third-generation cephalosporin use were relatively uniform in the three size categories. This study shows that it is possible for a hospital to benchmark its consumption with other hospitals that are similar in size. In this way, surveillance of antibiotic use can aid hospitals in targeting infection control efforts.

Generalized additive model demonstrates fluoroquinolone use/resistance relationships for Staphylococcus aureus

Mathematical models currently used to study the relationship between the prevalence of the resistance to an antibiotic and the amount of drug may not be adequate because they do not integrate temporal and area analyses simultaneously. Furthermore, the forms of such relationship are unknown. We applied the Generalized Additive Model (GAM) to study fluoroquinolone use and the incidence of fluoroquinolone-resistance in Staphylococcus aureus in our institution over a 3-year period. Overall institution and individual hospital unitrestricted analyses were performed. Relative risk (RR) observed for increasing fluoroquinolone use with a 4-month lag from the 25th percentile to the 75th percentile was 1.27 (95% CI: 1.13-1.42). In the surgery units, RR was 1.23 (95% CI: 1.01-1.50) for fluoroquinolone use with a 2-months lag. GAM enabled us to observe for the first time a significant temporal relationship between fluoroquinolone use and the incidence of fluoroquinolone-resistant nosocomial S. aureus isolates.

An International Multicenter Study of Antimicrobial Consumption and Resistance in Staphylococcus aureus Isolates from 15 Hospitals in 14 Countries

Antibiotic consumption during 1996 was measured in 15 large hospitals from 14 countries and 3000 consecutive Staphylococcus aureus samples were collected, allowing calculation of local resistance rates and typing of isolates. Antibiotic consumption data were converted to defined daily doses (DDD), and similar antibiotics were grouped if they belonged to the same therapeutic subgroup. Variations in hospital size were corrected by using DDD per 1000 bed-days. The total antibiotic consumption in the 15 hospitals varied between 296 DDD/1000 bed-days and 1108 DDD/1000 bed-days. Differences in the usage of therapeutical subgroups of antimicrobials varied significantly between hospitals. A positive correlation was found between S. aureus resistance to methicillin (MRSA) and consumption of beta-lactam combinations, between resistance to quinolones and consumption of beta-lactam combinations and carbapenems and resistance to aminoglycosides and consumption of beta-lactam combinations. The consumption of beta-lactamase-sensitive antibiotics was negatively correlated to resistance to methicillin, quinolones, and aminoglycosides. Usage of the different antimicrobial therapeutical subgroups was also correlated. Consumption of beta-lactamase-sensitive antibiotics (penicillin) was positively correlated to consumption of beta-lactamase-resistant penicillins and negatively correlated to consumption of carbapenems, quinolones, and glycopeptides, whereas consumption of cephalosporins was positively correlated to consumption of aminoglycosides, quinolones, and glycopeptides. In this study of hospitals with MRSA prevalence of between 0% and 63%, significant correlations were found between resistance and consumption of antimicrobials. These findings support the importance of antimicrobial consumption on resistance. An accompanying paper addresses the issue of antibiotic resistance and clonality of isolates.

Relationship between glycopeptide use and decreased susceptibility to teicoplanin in isolates of coagulase-negative staphylococci

To investigate the relationship between glycopeptide use and decreased susceptibility to teicoplanin in coagulase-negative staphylococci (CNS) isolates, data on teicoplanin susceptibility and glycopeptide use from existing microbiology laboratory and pharmacy databases were collected for the period between July 2000 and March 2001. Pooled data for the entire study period were first used to analyse associations. Univariate analysis showed that the incidence of CNS with decreased susceptibility to teicoplanin was significantly correlated with the use of glycopetides, particularly with vancomycin use. This association was confirmed by multivariate analysis. This study suggests that variations in antimicrobial resistance are related to variations in antimicrobial use in the model of CNS with decreased susceptibility to teicoplanin, thus confirming the usefulness of restricting antimicrobial prescribing as a means of controlling resistance.

Fluoroquinolones and the risk for methicillin-resistant Staphylococcus aureus in hospitalized patients

To determine whether fluoroquinolone exposure is a risk factor for the isolation of Staphylococcusaureus and whether the effect is different for methicillin-resistant S.aureus (MRSA) versus methicillin-susceptible S.aureus (MSSA), we studied two case groups. The first case group included 222 patients with nosocomially acquired MRSA. The second case group included 163 patients with nosocomially acquired MSSA. A total of 343 patients admitted concurrently served as controls. Outcome measures were the adjusted odds ratio (OR) for isolation of MRSA and MSSA after fluoroquinolone exposure. Exposure to both levofloxacin (OR 5.4; p < 0.0001) and ciprofloxacin (OR 2.2; p < 0.003) was associated with isolation of MRSA but not MSSA. After adjustment for multiple variables, both drugs remained risk factors for MRSA (levofloxacin OR 3.4; p < 0.0001; ciprofloxacin OR 2.5; p = 0.005) but not MSSA. Exposure to levofloxacin or ciprofloxacin is a significant risk factor for the isolation of MRSA, but not MSSA.

Methicillin resistant Staphylococcus aureus in the critically ill

Methicillin resistant Staphylococcus aureus (MRSA) is endemic within many hospitals worldwide. Critically ill patients on intensive care units have increased risk factors making them especially prone to nosocomially acquired infections. This review addresses the current situation regarding the evolution of MRSA and the techniques for identifying and epidemiologically typing it. It discusses specific risk factors, the morbidity and mortality associated with critically ill patients, and possibilities for future antibiotic treatments.

Optimizing Antibiotic Use in Hospitals: The Role of Population-Based Antibiotic Surveillance in Limiting Antibiotic Resistance

To minimize antibiotic resistance, pharmacists increasingly are becoming involved in antibiotic surveillance, formulation of antibiotic use policies, and day-to-day control of problematic antibiotic use. Population-based antibiotic surveillance has become common with the proliferation of electronic databases. The most widely applied measure of antibiotic consumption is the defined daily dose/1000 patient days. Most studies correlating antibiotic consumption with resistance have focused on antibiogram-related end points; antibiogram data generally reflect institutional nosocomial infection patterns. Most study designs have been derived from traditional epidemiology such as case-control with regression modeling or simple linear regression; however, these methods have limitations. Several experimental designs show promise. Many historical-control studies, including a multicentered study, suggest that population-based antibiotic surveillance and policy intervention can decrease antibiotic resistance in hospitals. Further research on the relationships among antibiotic surveillance, structured antibiotic policy interventions, and other microbiologic, patient-oriented, and economic end points is needed.

Contribution de la pression de sélection antibiotique dans l’acquisition de Staphylococcus aureus résistant à la méticilline (SARM) dans un centre hospitalier universitaire

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen, which causes severe morbidity and mortality in hospitals. Antibiotic pressure is recognised as an individual risk factor in the acquisition of MRSA, however, some authors suggest that antibiotic use must be considered as an ecological and collective problem on a unit or hospital scale. The objective of our study was to determine whether antibiotic pressure affects the acquisition of MRSA. The study was conducted during 1 year (from October 2000 to September 2001) at Besançon hospital. The analysis was based on the research of a correlation between incidence of MRSA acquisition, the colonisation pressure exerted by imported MRSA and use of antimicrobials ineffective against MRSA at the unit level. Univariate analysis showed that acquired MRSA cases were significantly correlated with the use of all antimicrobials, as well as with the use of each class of antimicrobial and with colonisation pressure. In multivariate analysis, the stratification of the units into consumer classes allowed us to eliminate the scale effect of each antimicrobial class and to characterise the impact of high antimicrobial use compared to weak antimicrobial. The highest risks of MRSA acquisition were observed for beta-lactams and quinolones. This study shows that "MRSA acquisition" is correlated to antibiotic use and highlights the need to improve antibiotic usage in the control of MRSA.

Relationship between spread of methicillin-resistant Staphylococcus aureus and antimicrobial use in a French university hospital

The objective of our study was to determine whether antibiotic pressure in the units of a teaching hospital affects the acquisition of methicillin-resistant Staphylococcus aureus (MRSA), independently of the other collective risk factors previously shown to be involved (MRSA colonization pressure, type of hospitalization unit, and care workload). The average incidence of acquisition of MRSA during the 1-year study period was 0.31 cases per 1000 days of hospitalization, and the use of ineffective antimicrobials reached 504.54 daily defined doses (DDDs) per 1000 days of hospitalization. Univariate analysis showed that acquisition of MRSA was significantly correlated with the use of all antimicrobials, as well as correlated with the use of each class of antimicrobial and with colonization pressure. Multivariate analysis with a Poisson regression model showed that the use of antimicrobials was associated with the incidence of acquisition of MRSA, independently of the other variables studied, but it did not allow us to determine the hierarchy of the different antimicrobial classes with respect to the effect.

Enteral vancomycin to control methicillin-resistant Staphylococcus aureus outbreak in mechanically ventilated patients

BACKGROUND

Screening for and treating gut carriage of methicillin-resistant Staphylococcus aureus (MRSA) may control transmission and subsequent endemicity of MRSA.

OBJECTIVE

Enteral vancomycin was evaluated as a measure to control an outbreak of MRSA infection in the intensive care unit (ICU).

METHODS

During the 8-month study of sequential design, 176 patients were admitted, 65 (37%) of whom required a minimum of 3 days of ventilation. Forty-four patients were studied in the first 5 months, during which traditional measures were reinforced (control group). During the following 3 months, 13 of 21 patients developed MRSA carriage and received 2 g/day of enteral vancomycin, with high standards of hygiene maintained (treatment group).

RESULTS

Thirty-three MRSA infections occurred in 22 patients (50%) in the control group, whereas 2 patients (9.5%) had 2 MRSA infections in the treatment group (P <.05 for carriage, infection rates, and episodes). Of the 33 MRSA infections in the control group, 27 were due to MRSA acquired in the ICU, whereas the 2 infections in the treatment group were primary endogenous (ie, caused by MRSA present in the patient's admission flora). The probability of developing an MRSA infection was reduced in patients receiving enteral vancomycin compared with patients in the control group (odds ratio, 0.37; 95% CI, 0.24-0.58). Enteral vancomycin significantly reduced the level of MRSA carriage; the mean carriage index was 1.01 in the control group versus 0.58 in the test group (P <.05). Neither vancomycin-resistant enterococci nor vancomycin-intermediate Staphylococcus aureus were isolated from either surveillance or diagnostic samples.

CONCLUSIONS

The eradication of MRSA gut carriage by enteral vancomycin in a small subset of ICU patients was effective in the control of an MRSA outbreak.

Surveillance of methicillin-resistant Staphylococcus aureus (MRSA) and Enterobacteriaceae producing extended-spectrum beta-lactamase (ESBLE) in Northern France: a five-year multicentre incidence study

In order to measure the incidence of methicillin-resistant Staphylococcus aureus (MRSA) and of Enterobacteriaceae producing extended-spectrum beta-lactamase (ESBLE), and to evaluate the impact of the national guidelines for multidrug-resistant bacteria (MDRB) prevention in hospitals of Northern France, a multicentre study was conducted for three months every year starting in 1996, in volunteer hospital laboratories. All clinical specimens positive for MRSA and ESBLE were prospectively surveyed. During the five-year surveillance period, the overall proportion of MRSA was 38.4% in the 28,534 strains of S. aureus, and that of ESBLE was 11.4% in the 6121 strains of Klebsiella pneumoniae and 47.7% in the 2353 strains of Enterobacter aerogenes. The overall incidence rates of clinical specimens positive for MRSA, ESBL-K. pneumoniae and E. aerogenes were 0.84. 0.05 and 0.12/1000 hospital-days (HD), respectively. In the 23 hospitals that participated in the survey every year, the proportion and incidence of ESBLE decreased. Hence, despite recommendations as for isolation precautions, MRSA remains poorly controlled and requires more effective measures.

Pseudomonas aeruginosa ventilator-associated pneumonia: comparison of episodes due to piperacillin-resistant versus piperacillin-susceptible organisms

We sought to determine the epidemiological characteristics of patients in an intensive care unit (ICU) who developed ventilator-associated pneumonia (VAP) caused by piperacillin-resistant Pseudomonas aeruginosa (PRPA; n=34) or piperacillin-susceptible P. aeruginosa (PSPA; n=101). According to univariate analysis, the factors associated with the development of PRPA VAP were presence of an underlying fatal medical condition, immunocompromised status, longer previous hospital stay, less-severe illness at the time of ICU admission, duration of mechanical ventilation before onset of VAP, number of classes of antibiotic received, and previous exposure to imipenem or fluoroquinolone. Multivariate logistic regression analysis identified the following significant independent factors: presence of an underlying fatal medical condition (odds ratio [OR], 5.6), previous fluoroquinolone use (OR, 4.6), and initial disease severity (OR, 0.8). We concluded that the clinical characteristics of patients who develop PRPA VAP differ from those of patients who develop PSPA VAP. Restricted fluoroquinolone use is the sole independent risk factor for PRPA VAP that is open to medical intervention.

Antimicrobial use prior to the acquisition of multiresistant bacteria

We assessed whether patients who acquired methicillin-resistant Staphylococcus aureus (MRSA) had less exposure to antimicrobial agents than did those who acquired Enterobacteriaceae that produced extended-spectrum beta-lactamase (ESbetaL). In a 6-month, prospective study, ESbetaL carriers had received antimicrobial therapy more often than had MRSA carriers. Amoxicillin-clavulanic acid, fluoroquinolones, and third-generation cephalosporins, especially ceftazidime, had been prescribed more often for ESbetaL carriers than for MRSA carriers.

The Nottingham Staphylococcus aureus population study: prevalence of MRSA among the elderly in a university hospital

A prevalence survey of methicillin-resistant Staphylococcus aureus (MRSA) in elderly patients (65 years and older) three weeks after admission to a university hospital was performed. Risk factors associated with hospital MRSA carriage were determined. The design was a cross-sectional patient-based study and all adult wards at the University Hospital Nottingham (1600 beds) were included. Three hundred and forty-two elderly individuals (65 years and older) were enrolled into the study on day 21 after admission. One hundred and twenty patients [35.08% (95% confidence intervals 29.93-40.25%)] carried S. aureus. MRSA was isolated from 54 patients. The MRSA prevalence was 158/1000 (95% CI 119-197/1000 patients). Independent risk factors for MRSA carriage in the hospital were exposure to ampicillin [adjusted odds ratio 4.1 (95% CI 1.28-13.14)] and ciprofloxacin [17.1 (95% CI 2.91-99.90)]. Forty-one MRSA isolates (75.9%) belonged to the epidemic type EMRSA 15, seven isolates to EMRSA 16 (12.9%) and six isolates were sporadic strains as determined by genetic typing. It can be expected that among this defined risk group, between 187 and 331 patients carried MRSA on discharge in the year 2000. MRSA carriage is frequent and detected in only 15% of actual carriers amongst elderly patients by routine clinical investigations three weeks after admission. The only significant risk factor identified by multivariate logistic regression was antibiotic chemotherapy. The repeated finding of a strong association between MRSA colonization and previous ciprofloxacin exposure demands attention and indicates that fluoroquinolones should be used prudently in institutions where MRSA is endemic.

Correlates of antibiotic use in Taiwan hospitals

OBJECTIVE

To determine factors that correlate with increased antibiotic use among adult inpatients in Taiwan.

DESIGN

Retrospective survey of medical records.

SETTING

14 acute-care hospitals (8 regional hospitals, 6 medical centers) in Taiwan.

PARTICIPANTS

A systematic probability sample from each hospital, totaling 663 adult inpatients who were discharged or had died in early 1999.

MEASUREMENTS

Infectious disease physicians at the 14 hospitals collected data from medical records regarding patient demographics, hospitalization, discharge diagnosis, and antibiotics received.

RESULTS

A total of 447 (67%) patients received antibiotics for an overall rate of 813 antibiotic-days (number of days patients received each antibiotic)/1,000 patient-days. Both the proportion of beds in intensive care units ([ICUs] Pearson correlation coefficient [r], 0.67; 95% confidence interval [CI 95], 0.36-0.89; P<.01) and the proportion of patients admitted to surgical services (r, 0.66; CI 95, 0.20-0.88; P=.01) correlated with the mean patient rate of antibiotic-days/hospital-day (MPAUD). In contrast, we found no correlation between the proportion of patients who received antibiotics and the MPAUD. Using multiple linear regression, medical center status was the only independent predictor for increased MPAUD (regression coefficient [b], 0.15; CI 95, 0.05-0.24; P<.01). There was no correlation between pooled rates of antibiotic-days/hospital-day and any hospital demographic factors. First-generation cephalosporin (39%) and aminoglycoside (24%) use accounted for the majority of antibiotic-days.

CONCLUSIONS

Antibiotic use is greater in medical centers than in regional hospitals and appears to be independent of surgical case mix or the proportion of ICU beds. Determination of multiple, independent measures of antibiotic use may be necessary to understand the relation between antibiotic use and resistance in hospital.

Nosocomial transmission of antibiotic-resistant microorganisms

The spread of nosocomially acquired, antibiotic-resistant microorganisms has grown dramatically over the past 20 years and has increasingly attracted the attention of academic inquiry. This article reviews recent epidemiological data about the trends and patterns of nosocomial transmission, presents clinical studies investigating mechanisms of cross-transmission, and discusses recent literature on preventive strategies aimed at reducing hand-carriage of antibiotic-resistant pathogens.

Risk factors for persistent carriage of methicillin-resistant Staphylococcus aureus

We determined risk factors associated with persistent carriage of methicillin-resistant Staphylococcus aureus (MRSA) among 102 patients enrolled in a double-blind, placebo-controlled trial of nasally administered mupirocin ointment. MRSA decolonization was unsuccessful in 77 (79%) of 98 patients who met the criteria for evaluation. By univariate analysis, 4 variables were found to be associated with persistent MRSA colonization (P < .1 for all 4): absence of mupirocin treatment, previous fluoroquinolone therapy, > or = 2 MRSA-positive body sites, and low-level mupirocin resistance. After multivariable Cox proportional hazards modeling, the presence of > or = 2 positive body sites (adjusted hazard ratio [AHR], 1.7; 95% confidence interval [CI], 1.0-2.9) and previous receipt of a fluoroquinolone (AHR, 1.8; 95% CI, 1.0-3.3) were independently associated with MRSA persistence, whereas nasal mupirocin tended to confer protection (AHR, 0.6; 95% CI, 0.4-1.0). Low-level mupirocin resistance was observed in 9 genotypically different MRSA strains and was not independently associated with chronic MRSA carriage (AHR, 1.5; 95% CI, 0.9-2.5). Our findings suggest that multisite MRSA carriage and previous receipt of a fluoroquinolone are independent risk factors for persistent MRSA colonization.

"Colonization pressure" and risk of acquisition of methicillin-resistant Staphylococcus aureus in a medical intensive care unit

OBJECTIVE

To determine the roles of "colonization pressure," work load or patient severity in patient acquisition of methicillin-resistant Staphylococcus aureus (MRSA) in intensive care units (ICUs).

DESIGN

Prospectively collected data from October 1996 through December 1998.

SETTING

A 12-bed medical ICU in a university-affiliated general hospital.

PATIENTS

Patients with risk factors for MRSA admitted to the ICU were screened within 72 hours of admission and weekly thereafter. MRSA was considered imported if detected during the first 72 hours of admission and nosocomial if detected only thereafter. Three screening strategies were used on admission during three consecutive periods.

INTERVENTIONS

The unit of time chosen for measurements was the week. Weekly colonization pressure (WCP) was defined as the number of MRSA-carrier patient-days/total number of patient-days. Patient severity (number of deaths, Simplified Acute Physiologic Score [SAPS] II), work load (number of admis sions, Omega score), and colonization pressure (number of MRSA carriers at the time of admission, WCP) were compared with the number of MRSA-nosocomial cases during the following week.

RESULTS

Of the 1,016 patients admitted over 116 weeks, 691 (68%) were screened. MRSA was imported in 91 (8.9%) admitted patients (13.1% of screened patients) and nosocomial in 46 (4.5%). The number of MRSA-nosocomial cases was correlated to the SAPS II (P=.007), the Omega 3 score (P=.007), the number of MRSA-imported cases (P=.01), WCP (P<.0001), and the screening period (P<.0001). In multivariate analysis, WCP was the only independent predictive factor for MRSA acquisition (P=.0002). Above 30% of WCP, the risk of acquisition of MRSA was approximately fivefold times higher (relative risk, 4.9; 95% confidence interval, 1.2-19.9; P<.0001).

CONCLUSION

Acquisition of MRSA in ICU patients is strongly and independently influenced by colonization pressure.

Excretion of beta-lactam antibiotics in sweat--a neglected mechanism for development of antibiotic resistance?

The concentrations of beta-lactam antibiotics after standard doses were measured in blood and apocrine (axilla) and eccrine (forearm) sweat from six adult healthy persons. All persons had ceftazidime (axilla, 28.4 microg/ml; forearm, 11 microg/ml) and ceftriaxone (axilla, 8.9 microg/ml; forearm, 2.5 microg/ml) in sweat, and one person had cefuroxime in sweat (axilla, 7.8 microg/ml) (all data are mean peaks). Three persons had benzylpenicillin (axilla, 2.6 to 0.1 microg/ml) and one had phenoxymethylpenicillin (axilla, 0.4 microg/ml) in sweat. Excretion of beta-lactam antibiotics in the sweat may explain why staphylococci so rapidly become resistant to these drugs.

Induction of fibronectin-binding proteins and increased adhesion of quinolone-resistant Staphylococcus aureus by subinhibitory levels of ciprofloxacin

We recently reported that strain EN1252a, a fluoroquinolone-resistant derivative of Staphylococcus aureus NCTC8325 with mutations in grlA and gyrA, expressed increased levels of fibronectin-binding proteins (FnBPs) and showed a significantly higher attachment to fibronectin-coated polymer surfaces after growth in the presence of subinhibitory concentrations of ciprofloxacin. The present study evaluated the occurrence and frequency of fluoroquinolone-induced FnBP-mediated adhesion in clinical isolates of fluoroquinolone-resistant methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA). Eight of ten MRSA isolates and four of six MSSA isolates with grlA and gyrA mutations exhibited significant increases in attachment to fibronectin-coated surfaces after growth in the presence of one-quarter the MIC of ciprofloxacin. Fluoroquinolone-induced FnBP-mediated adhesion of one clinical MRSA strain and the double mutant strain EN1252a also occurred on coverslips removed from the subcutaneous space of guinea pigs. For strain EN1252a, the regulation of fnb transcription by sub-MICs of ciprofloxacin was studied on reporter plasmids carrying fnb-luxAB fusions. One-quarter of the MIC of ciprofloxacin significantly increased fnbB, but not fnbA, promoter activity of the fluoroquinolone-resistant mutant but not its fluoroquinolone-susceptible parent ISP794. This response was abolished by pretreatment with rifampin, indicating an effect at the level of transcription. Activation of the fnbB promoter was not due to an indirect effect of ciprofloxacin on growth rate and still occurred in an agr mutant of strain EN1252a. These data suggest that sub-MIC levels of ciprofloxacin activate the fnbB promoter of some laboratory and clinical isolates, thus contributing to increased production of FnBP(s) and leading to higher levels of bacterial attachment to fibronectin-coated or subcutaneously implanted coverslips.