Rare fungal pathogens – upcoming guidelines: hyalohyphomycetes

On behalf of the ECMM and EFISG Study group Hyalohyphomycosis is a heterogeneous group of infections characterized by the presence of hyaline hyphae in tissues. The infecting fungi, belonging to several genera (Fusarium, Scedosporium, Acremonium, Scopulariopsis, Purpureocillium and Paecilomyces), are ubiquitous in the environment and commonly isolated from soil. Histopathological findings of septate, branching, hyaline hyphae are similar to those of aspergillosis. Therefore a definitive diagnosis requires isolation of the pathogens from infected sites. Blood cultures are often positive in case of invasive infection. Due to the variable susceptibility of these fungi to antifungal agents identification of the fungus grown on culture is important. As species identification based on morphological characteristics is difficult, molecular identification methods are often required. Antifungal susceptibility testing is recommended under certain circumstances to guide antifungal therapy, even if the clinical breakpoints have yet to be defined. Several inhouse molecular diagnostic tests have been developed, they appear promising but should be used only to supplement conventional laboratory tests. Given the lack of clinical trials, the scarcity of data and the potential publication bias, no solid recommendations for the management of these mycoses can be provided. Voriconazole represents the first line treatment of infections due to Fusarium spp and Scedosporium spp. Therapy should include surgical debridement where possible.