 The rising incidence of infections caused by extended-spectrum beta-lactamase ESBL producing Enterobacteriaceae is of worldwide dimensions, particularly in developing countries. At the American University of Beirut Medical Center AUB-MC, the proportion of ESBL producing E. coli ESBL-EC and K. pneumoniae ESBL-KP strains has risen from 2.5 and 9.8 to 22 and 27, respectively between 1999 and 2008. The rapid spread of these multi drug resistant pathogens prompted the study of factors aiming at limiting the ongoing transmission of these organisms. Infection control interventions, such as contact isolation of infected patients, have been used to control outbreaks of infections caused by ESBL producing organisms in settings where the pathogens were isolated from rectal and axillary samples, as well as from upper respiratory tract secretions. These few reports raise concern for colonization of infected patients at sites other than the primary site of infection. Colonization in the absence of outbreaks has so far not been looked at systematically, especially in a high-endemicity area such as Lebanon. The present study ultimately aims at assessing the usefulness of placing patients with ESBL-EC and ESBL-KP infections on contact isolation during their hospital stay, and whether this practice would limit the spread of such infections. This is a prospective study screening hospitalized patients with ESBL-EC and ESBL-KP infections for colonization with the same organism at sites other than the primary site of infection through cultures of the rectum, skin, nasopharynx, urine and, if applicable, wounds. Cases will be identified through the Clinical Microbiology Laboratory at AUBMC and study subjects will be enrolled according to the inclusionexclusion criteria. In addition to cultures of multiple body sites, molecular analysis will be performed on the isolated ESBL-producing strains to identify clonal relatedness. Cultures will be repeated monthly for a period of 6 months. The sample size is estimated at 100 patients over a two year period. The results of this study will have implications on infection control practices and will constitute a prerequisite for further studies in the future. 