Rapid diagnosis of disseminated histoplasmosis in tissues.

Disseminated histoplasmosis may resemble other disseminated infections, including mycobacterial, fungal, and parasitic diseases, and may be difficult to diagnose and treat in a timely fashion. Diagnosis may depend on microbiologic cultures that may take several weeks for definitive identification, with consequent prolonged hospitalization of the patient. An immunoperoxidase method is described for rapid diagnosis in tissues of Histoplasma capsulatum that can be applied to cytologic smears, frozen sections, and paraffin-embedded tissues processed by routine procedures. The stain can accurately distinguish histoplasma organisms from several other morphologically similar fungi or parasites, and can yield a definitive diagnosis in much less time than microbiologic culture.