In the described case of aspergillosis in an immunocompromised patient, which organism was identified in the sputum culture?

• A. Aspergillus fumigatus
• B. Candida albicans
• C. Pneumocystis jirovecii
• D. Histoplasma capsulatum

Answer: (A)

In patients with weakened immune systems, invasive lung infections are most commonly due to Aspergillus species, with Aspergillus fumigatus being the most frequent culprit. When a sputum culture grows Aspergillus fumigatus in this clinical setting, it fits the pattern of aspergillosis and supports that organism as the cause of the pulmonary infection. This organism is a mold with septate hyphae that tend to branch at acute angles, a detail that pathologists recognize on microscopic examination and helps distinguish it from other fungi. The other organisms listed are associated with different infections or contexts: Candida albicans is usually a mucosal inhabitant and colonizer rather than the typical cause of invasive pulmonary disease identified from sputum cultures; Pneumocystis jirovecii causes Pneumocystis pneumonia and is diagnosed by specialized staining or PCR rather than a routine culture; Histoplasma capsulatum causes histoplasmosis with its own geographic and clinical patterns. So identifying Aspergillus fumigatus in this setting best matches the described aspergillosis case.