Patients aged ≥ 18 years are eligible if they have acute leukemia, myelodysplasia or other underlying hematologic malignancy receiving chemotherapy with an expected duration of neutropenia (<500/mm3) >10 days. This includes allogeneic (but not autologous) hematopoietic stem cell transplantation. Patients with past history of IMI will be excluded, since for these patients secondary prophylaxis is advised.