Histoplasmosis

Histoplasma capsulatum is a dimorphic fungus that produces airborne microconidia. After inhalation, infection begins in the lungs. The host immune response may contain it there, or the infection may disseminate beyond the respiratory system. The first clinical question is not “Does this patient have histoplasmosis?” It is “How well is this patient tolerating the pulmonary illness, and is there evidence that it is spreading?” An older adult or a person with impaired immunity deserves a lower threshold for reassessment because dissemination is more likely in these groups. Pulmonary histoplasmosis can be mild and stable, but a respiratory presentation is not specific enough to identify the organism by appearance alone. Trend the patient’s oxygenation, work of breathing, temperature, blood pressure, and mental status rather than relying on a single reassuring observation. New hepatosplenomegaly, adrenal insufficiency, or neurologic findings shifts concern from a limited lung infection toward disseminated disease. The 2025 treatment update changes an old exam reflex: an immunocompetent adult or child with mild acute pulmonary histoplasmosis does not automatically require itraconazole. Observation with symptomatic support is acceptable when the illness...