Patients with negative blood cultures represent 85-90 % from all patients with a blood culture taken during hospital admissions. This population usually includes an heterogeneous group of patients that are admitted because of an infectious diseases or febrile syndrome in which performing a blood culture is required. There is scarce evidence about the clinical characteristics and the antibiotic treatment given to these patients. This project will be developped in two phases with an specific target in each one:

• Phase I (a cohort study of patient with blood cultured taken): the investigators aim to analyse the clinical and therapeutics characteristics, outcomes and antimicrobial stewardship oppotunities in a population of patients with negative blood culture. The investigators aim to compare the outcomes and antimicrobial stewardship opportunities with those in patients with positive blood culture.
• Phase II: The investigators will develop a cluster randomised control trial to evaluate the implementation of a targeted antimicrobial stewardship intervention in patients with negative blood culture (based on 3rd and 5th day audits). The effect of the intervention on the quality of antimicrobial use (duration and de-escalation), long of stay and mortality will be analysed.

Inclusion Criteria:

• Health professionals in charge of patients with negative hemoculture and active antibiotherapy within 48 hours of extraction; and that belong to a clinical unit that has been assigned to the intervention arm.

Exclusion Criteria:

• Health professionals in charge of patients who, even if they meet the criteria described above, will not be considered to have a foreseeable death within <72hrs from the hemoculture extraction or a positive hemoculture in the seven days prior to the extraction of the negative hemoculture.