Neutropenia is usually defined as a WBC count less than 4,000/mm3. Some conditions associated with neutropenia include (1) conditions associated with pancytopenia, such as megaloblastic anemia, aplastic anemia, acute or aleukemic leukemia, hypersplenism of varying etiology (e.g., cirrhosis, systemic lupus, Gaucher’s disease), and paroxysmal nocturnal hemoglobinuria, (2) drug-induced neutropenia (agranulocytosis), (3) certain infections, such as typhoid, some viral infections (e.g., Epstein-Barr, in the first week of illness, and the hepatitis viruses), overwhelming bacterial infection (septicemia, miliary tuberculosis), and (4) cyclic and chronic idiopathic neutropenia. In one study, neutropenia was present in 3% of inpatient children and 7% of outpatient children. In another study, the median duration of isolated neutropenia in children was 7-14 days, with total duration of 30 days in 70% of patients. In two studies, the risk of developing an infection in a febrile neutropenic child who otherwise appears well was about 3%-5%.