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

Extended-spectrum β-lactamases: implications for the clinical microbiology laboratory, therapy, and infection control

Extended-spectrum beta-lactamase (ESBL) producing gram-negative bacilli are a growing concern in human medicine today. When producing these enzymes, organisms (mostly K. pneumoniae and E. coli) become highly efficient at inactivating the newer third-generation cephaloporins (such as cefotaxime, ceftazidime, and ceftriaxone). In addition, ESBL-producing bacteria are frequently resistant to many classes of non-beta-lactam antibiotics, resulting in difficult-to-treat infections. This review gives an introduction into the topic and is focused on various aspects of ESBLs; it covers the current epidemiology, the problems of ESBL detection and the clinical relevance of infections caused by ESBL-producing organisms. Therapeutic options and potential strategies for dealing with this growing problem are also discussed in this article.

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.

Réduction significative des infections nosocomiales : analyse stratifiée des enquêtes nationales de prévalence conduites en 1996 et 2001 dans l’inter-région Nord

BACKGROUND

In France, repeated prevalence studies of nosocomial infections (NI) are part of governmental plan against NI built in 1995 by the Ministry of Health. To evaluate strand of NI prevalence, we performed a comparative analysis of two successive national point-prevalence surveys occurring in 1996 and 2001 for the Northern France.

METHOD

Comparison concerned the hospitals, which participated in the two studies of 1996 and 2001 in Northern France. The studies were designed as a point-prevalence survey on voluntary basis. For each patient, risk factors and presence of active NI at the day of the study were recorded on standardised form. Criteria of NI used were these of "100 recommendations" of CTIN and of CCLIN North guideline. Prevalence rate (PR) and frequency of risk factors were compared. The risk factors significantly linked to NI by logistic regression were used to build a score of five risk levels of NI (PREVARISK) allowing an adjusted comparison of the 2 years.

RESULTS

Total of 161 hospitals participated at the two studies, including respectively 61 422 and 58 749 patients. Between 1996 and 2001, crude PR of infected patients and of NI decreased respectively from 7.8% to 7.3% and 9.0% to 8.0% (P < 10(-4)), so then relative decreases were of 6.4% and 11.1%. In contrast, the frequency of risk factors, except surgery in the past 30 days, significantly increased. Risk factors included in PREVARISK were: age >65 years, immunosuppression, surgery in the past 30 days, urinary tract and central catheter. In patients with a low risk level (PREVARISK = 0), the relative decrease of infected patients and NI PR were of 17% and 19%. The decrease was not significant for patients with high risk level (PREVARISK >/= 3).

CONCLUSION

Our analyses show a decrease of PR adjusted on risk factors, especially in patients with a low risk level. These result suggest an efficacy of program against NI in studied hospitals especially for patients for whom NI would be potentially avoidable.

Relationship between molecular epidemiology and antibiotic susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) in a French teaching hospital

The objective of this study was to investigate the relationship between molecular epidemiology and antibiotic susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) over a period of 4 years. The antibiotype of all MRSA isolates that were identified during a yearly period of 3 months was determined; 50 consecutive non-replicate MRSA isolates were typed each year. Susceptibility rates to gentamicin, tobramycin and ofloxacin remained stable (95, 16 and 4 %, respectively). In contrast, the proportion of MRSA isolates susceptible to erythromycin increased progressively from 10.5 to 32.5 % (P < 0.001). PFGE analysis of genomic DNA from 200 isolates revealed the presence of 15 different clones. Two epidemic clones were identified, which contained 150 (clone A) and 28 (clone C) isolates. Non-epidemic strains were more frequently susceptible to ofloxacin (31.8 versus 1.1 %) and tobramycin (45.4 versus 16.8 %) than epidemic strains; those isolates that were susceptible to all antibiotics tested belonged to sporadic clones. The increase of erythromycin susceptibility within MRSA isolates was caused by the emergence of clone C. This study suggests that when selection pressure exerted by an antibiotic is insufficient (i.e. below a threshold level), fitness advantages play a predominant role in the dissemination of MRSA clones. The balance between the selection pressure exerted by antibiotics and the disadvantage of lower replication rates of resistant strains in the absence of antibiotics complicates the biological model of clonal dissemination of epidemic MRSA strains.

Antimicrobial resistance in Staphylococcus aureus at the University of Chicago Hospitals: a 15-year longitudinal assessment in a large university-based hospital

OBJECTIVES

To describe a longitudinal profile of resistance to beta-lactam antimicrobials among isolates of Staphylococcus aureus at a large university teaching hospital and to evaluate the impact of the methicillin resistance phenotype on resistance trends for non-beta-lactam antimicrobials.

DESIGN

Retrospective evaluation of antimicrobial susceptibility data for all 17,287 S. aureus isolates obtained from January 1986 through December 2000.

SETTING

The University of Chicago Hospitals, a family of tertiary-care, university-affiliated hospitals in Chicago, Illinois, consisting of 547 adult and pediatric beds.

RESULTS

The annual rate of resistance to methicillin increased from 13% in 1986 to 28% in 2000 (P < .001) and has not plateaued. For each non-beta-lactam antimicrobial tested, the annual rates of resistance were far higher among methicillin-resistant S. aureus (MRSA) isolates than among methicillin-susceptible S. aureus (MSSA) isolates. The annual rates of resistance to the macrolide, lincosamide, and streptogramin (MLS) antimicrobials erythromycin and clindamycin increased among MSSA isolates (P < .01), but remained lower than 20%. Resistance to the MLS antimicrobials was higher among MRSA isolates (higher than 60%), but the annual rate decreased significantly during the study (P < .01).

CONCLUSION

The prevalence of methicillin resistance among S. aureus isolates has continued to increase; resistance to non-beta-lactam antimicrobials is far more common among MRSA isolates. Recent decreases in the proportion of MRSA isolates resistant to non-beta-lactam antimicrobials suggest important changes in the epidemiology of this pathogen.