 Data collection Medical records of in-patient admissions and microbiology and pharmacy databases will be reviewed. Data collected at the study enrollment will include: patient demographics, transfer from another hospital, resident of a long term facility or nursing home, previous hospitalization within one year, ambulatory status, requirement for chronic hemodialysis, presence of a central venous catheter CVC, and ICU stay and surgical procedures in the 30 days prior to study inclusion. A composite score of co-morbid illnesses will be derived using the Charlson score. The severity of illness at presentation will be quantified using the criteria of McCabe and Jackson. Antibiotics administered during a 30-day period prior to study enrollment and for at least 48 hours will be recorded. For the risk factors analysis, oral and intravenous antibiotic exposure will be analysed by individual antibiotics and by classes, and will include penicillins, vancomycin, cephalosporins, antibiotics with predominantly anaerobic activity metronidazole and clindamycin, aminoglycosides, quinolones, and carbapenems. Length of stay LOS after infection diagnosis, management of infections, timing and type of antimicrobial therapy, results of follow-up clinical cultures if any, hematogenous complications and death will be also extracted from medical records. Microbiology records will be also reviewed for recovery of vancomycin resistant enterococci VRE or methicillin-resistant S. aureus MRSA in the 12 months prior to the study enrollment. All patients with infections caused by ESBL-producing Enterobacteriaceae will be followed up to hospital discharge or death. 