This study compares the safety (non-inferiority) of short treatment (72 hours) versus extended treatment (at least 9 days) with an anti-pseudomonal carbapenem for hematology patients with unexplained high risk febrile neutropenia. We hypothesize that a more restrictive use of broad-spectrum antibiotic use of three days in unexplained fever in neutropenic hematology patients is non-inferior to the present extended use during at least 9 days which would lead to a more restrictive use of antibiotics and less multiresistant strains of bacteria, costs and hospitalization length in the future.