Histoplasma Endocarditis: Clinical and Mycologic Features and Outcomes

Objectives: To define the salient clinical and microbiologic characteristics and outcome of infective endocarditis caused by Histoplasma capsulatum.

Methods: Case report and review of 43 literature cases.

Results: Infection involved both native (36 cases) and prosthetic (7) heart valves, had a high rate of systemic embolization (58%), and a more delayed diagnosis than bacterial endocarditis. Cardiac involvement generally occurred on mitral and/or aortic valves, and almost always in the setting of disseminated disease. Antemortem diagnosis was best made by serology (serum antibody titers or urinary antigen) or culture of blood (positive in <20% of cases), bone marrow, excised valves, and other non-blood specimens. Other diagnostic methods included histopathology and immunofluorescent staining of tissue samples. Untreated infection was uniformly fatal. Prolonged antifungal therapy with amphotericin B, without surgical intervention, appeared more effective than for Candida endocarditis.

Conclusions: Histoplasma endocarditis is an infrequent but important cause of left-sided, blood culture-negative endocarditis. Its true prevalence may be underestimated because of the relative difficulty in making a precise microbiologic diagnosis. Amphotericin B therapy appears more effective than for Candida endocarditis, while the role for azole treatment and secondary prophylaxis remains uncertain. Indications for surgical valve replacement are similar to those for bacterial endocarditis.