The identification of all cases (44 patients) was carried out from the database of microbiology, University Hospital Reina Sofía and the University Hospital of Jerez. For the identification of controls, in case of neutropenic patients, all colonized patients that were included during the study period did not receive any decolonitation treatment; in case of non-neutropenic patients it was studied a paired control by the presence of risk factors that indicated the beginning of decolonitation treatment.

Inclusion Criteria:

• Patients with intestinal colonization by Klebsiella pneumoniae, defined as the presence of a positive rectal swab culture at least 7 days prior to initiation of therapy; and patients considered at risk of developing an invasive infection by Klebsiella pneumoniae:
• Surgery in two weeks
• Transplant in two weeks
• Require medical intervention or has a clinical situation that may predispose to the development of a serious infection (chemotherapy, immunosuppression or neutropenia)
• Recurrent or severe infections
• Institution admission
• Fragile patients at high risk of readmission.

Exclusion Criteria:

• The presence of an active infection for Klebsiella Pneumoniae.
• Concomitant use of systemic antibiotics in the 14 days before the start of decolonization therapy.

The sample consists of all patients who received therapy desconolizacion against Klebsiella Pneumoniae versus those not receiving such therapy.