Exclusion of Mucorales Co-Infection in a Patient with Aspergillus flavus Sinusitis by Fluorescence In Situ Hybridization (FISH)

Invasive fungal infections are associated with increased mortality in hematological patients. Despite considerable advances in antifungal therapy, the evaluation of suspected treatment failure is a common clinical challenge requiring extensive diagnostic testing to rule out potential causes, such as mixed infections. We present a 64-year-old patient with secondary AML, diabetes mellitus, febrile neutropenia, and sinusitis. While cultures from nasal tissue grew Aspergillus flavus, a microscopic examination of the tissue was suggestive of concomitant mucormycosis. However, fluorescence in situ hybridization (FISH) using specific probes targeting Aspergillus and Mucorales species ruled out mixed infection. This was confirmed by specific qPCR assays amplifying the DNA of Aspergillus, but not of Mucorales. These results provided a rational basis for step-down targeted therapy, i.e., the patient received posaconazole after seven days of calculated dual therapy with liposomal amphotericin B and posaconazole. Despite clinical response to the antifungal therapy, he died due to the progression of the underlying disease within two weeks after diagnosis of fungal infection. Molecular diagnostics applied to tissue blocks may reveal useful information on the etiology of invasive fungal infections, including challenging situations, such as with mixed infections. A thorough understanding of fungal etiology facilitates targeted therapy that may improve therapeutic success while limiting side effects.Peer Reviewe

Rapid Diagnosis of Central Nervous System Scedosporiosis by Specific Quantitative Polymerase Chain Reaction Applied to Formalin-Fixed, Paraffin-Embedded Tissue

Scedosporium (S.) apiospermum is a typical mold causing cerebral abscesses, often after near-drowning. Infections are associated with high morbidity and mortality due to diagnostic challenges including the need for prolonged incubation of cultures. In addition, histopathological differentiation from other filamentous fungi, including Aspergillus fumigatus, may not be possible, excluding early specific diagnosis and targeted therapy. Polymerase chain reaction (PCR) on tissue samples can rapidly identify fungi, leading to an earlier adequate treatment. Due to an extensive spectrum of causative fungi, broad-range PCRs with amplicon sequencing have been endorsed as the best DNA amplification strategy. We herein describe a case with brain abscesses due to S. apiospermum in a 66-year-old immunocompromised female patient. While broad-range PCR failed to identify a fungal pathogen from a cerebral biopsy demonstrating hyaline mold hyphae, specific quantitative PCR (qPCR) identified Scedosporium and ruled out Aspergillus, the most prevalent agent of central nervous system mold infection. A panel of specific qPCR assays, guided by the morphology of fungal elements in tissue or as a multiplex assay, may be a successful molecular approach to identify fungal agents of brain abscesses. This also applies in the presence of negative broad-range fungal PCR, therefore providing diagnostic and therapeutic potential for early specific management and improvement of patient clinical outcome