β-1,3-d-Glucan and Galactomannan as Biomarkers for the Detection of Invasive Geotrichum and Magnusiomyces Infections: a Retrospective Evaluation.

Magnusiomyces and Geotrichum species are ascomycetous yeasts that can cause potentially life-threatening invasive fungal infections commonly referred to as geotrichosis. In this study, we aimed to estimate the incidence and mortality of these infections in a German tertiary care center. Furthermore, we evaluated the suitability of the fungal biomarkers galactomannan (GM) and β-1,3-d-glucan (BDG), which are both recommended as surrogate markers for Magnusiomyces capitatus infection by the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) and the European Confederation of Medical Mycology (ECMM) joint clinical guidelines for the diagnosis and management of rare invasive yeast infections for detection of invasive geotrichosis. Cases meeting the inclusion criteria for invasive Magnusiomyces/Geotrichum infection were retrospectively identified. Serum samples and culture supernatants were analyzed with two commercially available fungal antigen tests (Platelia Aspergillus Ag EIA and Wako β-glucan test). For a control cohort, outpatient samples sent for lues testing were included. Thirty-eight cases of Magnusiomyces/Geotrichum infection were identified over an 11-year observation period. In the majority of cases, the fungus was isolated from intra-abdominal specimens of patients with a history of abdominal surgery/procedures (n = 32). All cases of fungemia occurred exclusively in haemato-oncologic patients (n = 14). Thirty-day survival was 42% in the fungemia and 43% in the intra-abdominal geotrichosis group. Serum samples were available for 23 patients (14 bloodstream and nine intra-abdominal infections). While BDG sensitivity was 65%, none of the sera was GM positive. This finding was supported by in vitro experiments analyzing fungal culture supernatants: M. capitatus secretes significant amounts of BDG but not GM. Specificity was 96% for BDG and 100% for GM. Magnusiomyces and Geotrichum infections are not limited to haemato-oncologic patients. Contrasting the current ESCMID/ECMM recommendation, our results indicate that GM is no suitable biomarker for the diagnosis of Magnusiomyces infection. Contrarily, BDG sensitivity is comparable to that of candidemia.