Study 3. For the analysis of cost, outcome impact and length of stay associated to target infections caused by CRE (objective 3), a matched cohorts study will be performed. The cohorts will be formed by selected patients with infections due to CRE and the patients with infections due to CSE (identical to the CSE control group above). Additionally, a control group of admitted patients not infected by CRE or CSE will be studied (identical to the admitted control group above).