36-15: Other Opportunistic Mold Infections

Fungi previously considered to be harmless colonizers, including Pseudallescheria boydii (Scedosporium apiospermum), Scedosporium prolificans, Fusarium, Paecilomyces, Trichoderma longibrachiatium, and Trichosporon, are now significant pathogens in immunocompromised patients. Opportunistic infections with these agents are seen in patients being treated for hematologic malignancies, in hematopoietic stem cell or organ transplant recipients, and in those receiving broad-spectrum antifungal prophylaxis. Infection may be localized in the skin, lungs, or sinuses, or widespread disease may appear with lesions in multiple organs. Fusariosis should be suspected in severely immunosuppressed persons in whom multiple, painful skin lesions develop; blood cultures are often positive. Sinus infection may cause bony erosion. Infection in subcutaneous tissues following traumatic inoculation may develop as a well-circumscribed cyst or as an ulcer.

Nonpigmented septate hyphae are seen in tissue and are indistinguishable from those of Aspergillus when infections are due to S apiospermum or species of Fusarium, Paecilomyces, Penicillium, or other hyaline molds. Spores or mycetoma-like granules are rarely present in tissue. The differentiation of S apiospermum and Aspergillus is particularly important, since the former is uniformly resistant to amphotericin B but may be sensitive to azole antifungals (eg, voriconazole). Treatment of fusariosis may include amphotericin, voriconazole, or combination therapy; there are limited data on the use of isavuconazole or posaconazole for this disease. In addition to antifungal therapy, reversal of underlying immunosuppression is an essential component of treatment for these invasive mold infections.

Infection by melanin-pigmented dematiaceous or “black” molds is designated as phaeohyphomycosis. These black molds (eg, Exophiala, Bipolaris, Cladophialophora, Curvularia, Alternaria) are common in the environment, especially on decaying vegetation. In tissues of patients with phaeohyphomycosis, the mold is seen as black or faintly brown hyphae, yeast cells, or both. Culture on appropriate medium is needed to identify the agent. Matrix assisted laser desorption ionization-time of flight mass spectrometry may be used for identification in specialized centers. Histologic demonstration of these organisms provides definitive evidence of invasive infection; positive cultures must be interpreted cautiously and not assumed to be contaminants in immunocompromised hosts.