Diagnosis of systemic histoplasmosis in patients with AIDS

To compare various laboratory methods for diagnosis of systemic histoplasmosis, we retrospectively reviewed the charts of 165 patients with AIDS (acquired immunodeficiency syndrome). In eight of those patients, systemic histoplasmosis was confirmed by laboratory techniques. The laboratory methods used were histomorphology and microbiology. Tissues and fluids used for fungal cultures and histochemical stains included blood, bone marrow, lung, skin, pleura, esophagus and colon biopsy specimens, sputum, cerebrospinal fluid, bronchial washing/brushing, and pleural and peritoneal fluids. Results were positive in 83% of blood cultures and 71% of bone marrow cultures, making these tissues the best sources of Histoplasma organisms for microbiologic study. Similarly, Histoplasma sp could be demonstrated by fungal stains in 75% of bone marrow biopsy specimens as the main source for morphologic documentation of systemic histoplasmosis. The other tissues and fluids were only occasionally positive either microbiologically or morphologically. There was cross-positivity between morphologic and microbiologic methods in 80% of confirmed cases, making both methods equally reliable. However, the results were obtained within 48 hours by histomorphology, allowing prompt initiation of antifungal therapy. Although more specific results were produced by microbiologic methods, it took 18 to 35 days to grow the organism.