Rare Yeast Infections: Risk Factors, Clinical Manifestations, Treatment, and Special Considerations

Purpose of Review: Rare yeasts include Trichosporon, Malassezia, Saprochaete, Kodamaea, Rhodotorula, Saccharomyces, Pseudozyma, Sporobolomyces, Exophiala, Lacazia, Emmonsia, and Wickerhamomyces (Pichia). In this review, we focus on the taxonomy, microbiology, risk factors, clinical manifestations, and treatment of rare yeasts. Recent Findings: Most rare yeasts are commonly encountered in the environment but infrequently cause infection in humans. Many of these organisms cause superficial skin infections in normal hosts. Most serious infections occur in immunocompromised hosts and/or in the presence of medical devices, especially intravascular catheters, and usually present as fungemia. Recent advances in DNA sequencing have led to taxonomic reclassification of some species which may not be reflected in older literature. The gold standard for diagnosis of rare yeast infections is still microscopy and culture based; however, molecular-based methods of diagnosis such as DNA sequencing or matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) are promising for speciation. Antifungal susceptibility varies by organism, but most favorable outcomes reported have been with amphotericin B or voriconazole. In general, mortality tends to be high. Summary: Advances in health care and improved molecular diagnostics are expanding the species of rare yeasts that are being recognized as human pathogens. Further research is needed to improve our understanding of the pathogenicity of these organisms so as to optimize therapy and improve outcomes.