Emerging Filamentous Basidiomycetes as Opportunistic Human Pathogens: Diagnostic and Antifungal Challenges in a...

Background/Objectives: Filamentous basidiomycetes are environmental fungi that rarely cause human infection but are increasingly recognized as opportunistic pathogens, particularly in immunocompromised hosts. However, their clinical epidemiology and antifungal management data remain limited. Methods: We conducted a retrospective study of patients with filamentous basidiomycetes isolated from clinical specimens at King Chulalongkorn Memorial Hospital, Thailand, between 2019 and 2025. Species identification was performed using internal transcribed spacer (ITS) or D1/D2 ribosomal DNA sequencing. Demographic characteristics, clinical features, antifungal management, and outcomes were analyzed. Results: Fourteen patients were identified with a mean age of 61.2 ± 18.3 (29-90), and 71.4% were female. In these patients, pulmonary infection was most common (64.3%), followed by ocular (14.3%), cutaneous (14.3%), and central-line-associated infection (7.1%). Bronchoalveolar lavage was the most frequent specimen (64.3%). ITS/D1D2 sequencing revealed broad species diversity, including Schizophyllum commune (n = 3), Candolleomyces spp. (n = 3), Coprinopsis cinerea, Fomitopsis spp., Geliporus exilisporus, Odontoefibula orientalis, Irpex laceratus, Volvariella volvacea, Deconica coprophila, and Agaricales spp. Antifungal therapy was largely empirical, with voriconazole used most frequently (46.6%). Overall, 85.7% of patients improved, whereas 14.3% did not respond clinically. Conclusions: Emerging filamentous basidiomycetes demonstrate substantial species diversity and pose ongoing diagnostic and antifungal management challenges. The absence of standardized susceptibility testing and clinical breakpoints may contribute to therapeutic uncertainty and challenges in antifungal selection. Integrating molecular diagnostics into routine clinical workflows may enhance antifungal stewardship in rare mold infections.