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Rapid diagnosis of Histoplasma capsulatum endocarditis using the Histoplasma capsulatum AccuProbe directly on the excised valve



Rapid diagnosis of Histoplasma capsulatum endocarditis using the Histoplasma capsulatum AccuProbe directly on the excised valve



Abstracts of the General Meeting of the American Society for Microbiology 101: 239



Background: Histoplasma capsulatum is an infrequent, but serious cause of endocarditis. The definitive diagnosis requires culture with extended incubation. When cultures are positive, confirmatory testing is needed to exclude a contaminating environmental mold with similar conidiation. The application of molecular methods, however, directly on excised tissue could achieve an accurate diagnosis, without the delays of culture. The AccuProbe(R) is a rapid method for the confirmation of Histoplasma capsulatum in culture, but has not been used for direct detection on the clinical specimen. Methods: The histopathology of the excised aortic valve of a 58 year old man with endocarditis demonstrated large vegetations that consisted of a mixture of yeast forms and fibrin. Based on morphologic features, these were thought to represent H. capsulatum. We attempted to identify the fungus present by using the Histoplasma capsulatum AccuProbe(R) directly on the excised valvular tissue, given the abundance of the yeast present. Apart from additional vortexing, portions of the valve containing vegetations were processed according to the manufacturer's instructions and probed using both the Histoplasma capsulatum AccuProbe(R) and, as a control, the Coccidioides immitis AccuProbe(R). Results: The cutoff for positivity in this assay is 50,000 relative light units (RLU). The signal produced using the H. capsulatum AccuProbe(R) in our specimen was 153,961 RLU, strongly positive, while the signal generated with the C. immitis AccuProbe(R) was only 17,539 RLU, clearly negative. One week later the culture grew H. capsulatum, which was also confirmed with the Histoplasma capsulatum AccuProbe(R). Conclusion: Although additional studies are needed, our findings suggest that the Histoplasma capsulatum AccuProbe(R) may be used for the rapid diagnosis of endocarditis caused by Histoplasma capsulatum, if a sufficient number of organisms are present in the tissue.

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