The purpose of this study is to investigate the risk factor, molecular character and susceptibility change for recurrent ESBL-producing Enterobacteriaceae bacteremia

1. To characterize the genotypes of the pathogens isolated from recurrent ESBL-EK bacteremia versus non-recurrent ESBL-EK bacteremia to differentiate relapse from reinfection

   • recurrent versus non-recurrent
   • relapse versus reinfection

2. To correlate the patient characteristics, clinical manifestations, severity of illness (the modified Pitt bacteremia score), diagnosis of deep-site infection, co-morbid conditions (including diabetes mellitus, hepatic and renal dysfunction), length of stay in ICU/hospitalization, the presence of invasive procedures, source of pathogen (community acquired or nosocomial infection), antimicrobial regimen (i.e carbapenems versus non-carbapenems(flomoxef or quinolones), microbiological characteristics (E coli and Kleb. pneumoniae) and outcome endpoints (clinical outcome and mortality) with ESBL recurrence and genotypes

Inclusion Criteria:

• Adult patients (age>=18 years) with at least one episode of ESBL-EK bloodstream infection from August 2004 to July 2010

Exclusion Criteria:

• Patients who died within 48h after first episode of ESBL-EK bloodstream infection

In a tertiary care hospital, every adult patient with at least one episode of ESBL-EK bloodstream infection from August 2004 to July 2010 will be recruited into this study. Patients who died within 48h after first episode of ESBL-EK bloodstream infection will be excluded.