Risk Factors for Piperacillin/Tazobactam Resistance in Extended-Spectrum Beta-Lactamase (ESBL) Producing Organisms

Inclusion Criteria: * Clinical information is collected by chart review of "case" and "control" patients. * A "case A" patient is defined as follows: One or more clinical cultures are positive for an ESBL producing bacteria and the organism is piperacillin/tazobactam resistant. * A "case B" patient is defined as follows: One or more clinical cultures are positive for an ESBL producing bacteria and the organism is piperacillin/tazobactam susceptible. * Additionally, 1 control patient in the hospital at the same time as the case patients will be randomly selected for each case and are not in either case group. Exclusion Criteria: * Patients \< 18 years of age