A 56-year-old man is undergoing chemotherapy for leukemia. He has developed fever, nonproductive cough, dyspnea, pleuritic chest pain, and hemoptysis over the past week. A chest CT scan shows multiple 1- to 4-cm nodular densities having surrounding areas of ground-glass infiltrate (halo sign). Bronchoalveolar lavage is performed, and microscopic examination of the fluid shows narrow branching septate hyphae. A CBC shows Hgb, 13 g/dL; Hct, 38.7%; WBC count, 2000/mL; and platelet count, 200,100/mL. He has most likely developed an infection with which of the following organisms?

There are several patterns of pulmonary involvement with Aspergillus spp. Immunocompromised patients with neutropenia may develop invasive aspergillosis. Other patterns include allergic bronchopulmonary aspergillosis in persons with asthma and an aspergilloma, or fungus ball, colonizing a cavitary lesion of tuberculosis or bronchiectasis. Candidiasis may also develop in the setting of neutropenia, but less commonly causes extensive lung involvement, appears as budding cells with pseudohyphae, and more likely produces an oral, nasal, or pharyngeal infection. Cryptococcosis can cause extensive pulmonary infections, particularly with loss of cell-mediated immunity, and the organisms have large mucoid capsules and exhibit narrow-based budding. Moraxella is a bacterial organism most often causing sinusitis, otitis, and upper respiratory infections. Mucor appears as broad, non-septated hyphae and is most often a complication of diabetic ketoacidosis, with nasal involvement.