Cost-effectiveness analysis of an Antimicrobial Stewardship program in Regione Lombardia: RF-net2018 is a prospective, experimental, multicenter, pre-post study, whose objectives are the evaluation of the efficiency of economic resources allocated to the antimicrobial stewardship program (AMS) in patients with infection and in patients with infections caused by carbapenem-resistant gram-negative (CR-GN) bacteria, identified in a network of 18 hospital facilities participating in our study. Moreover, this study aims to compare hospital mortality among patients admitted to the facilities participating in the study before and during the implementation of the AMS project. The study will include two main phases of analysis: the pre-intervention-phase and the intervention phase, both of 6 months duration. The pre-intervention phase will serve as a control for the intervention phase. The intervention phase is represented by antimicrobial stewardship activities which have been implemented in the network of 18 hospital facilities and that include a group of activities listed above (Hospital commitment, Tracking and reporting, Action and Education). Data source and analysis for the cost-effectiveness analysis, using month-department as statistical unit, are regional data: Discharge record ICD-9 codes (identification of target population 1, 2, 3, average days of hospitalization and mortality), R file (for antibiotic drug consumption month-ward) and Microbio (identification of target population 2, CR-GN and MRSA bacteremia and Cases of C. difficile infection). For what concerns healthcare costs data, each Management control office of the 18 facilities has to provide: AVERAGE HOSPITALISATION DAYS, NUMBER OF HOSPITALIZED AND TRANSFERRED PATIENTS and HEALTHCARE COSTS (healthcare personnel, diagnostic services, surgical interventions and consumption of operating rooms).