- Study 2: The CRE case group will be formed by 248 patients with CRE infections selected from the study 1 cohort. Per each CRE case, one CSE control patient and 3 non-infected controls will be selected. Because of possible heterogeneity due to the different infection types, we have chosen to over sample by a ratio of 248/201*100%. The number of matched controls has been chosen to be four which is well known to well approximate the power of full cohort data.