Isavuconazole Breakthrough Disseminated *Fusarium fujikuroi* Infection in a Patient with Allogeneic Hematopoietic Stem Cell Transplant: Diagnostic and Therapeutic Challenges – A Case Report

# Introduction This case report illustrates the diagnostic challenges and complexities in the treatment of disseminated fusariosis. # Case An 18-year-old patient received a second allogeneic hematopoietic stem cell transplant (HSCT) 5 months after the first HSCT. Two days post-transplant, the patient presented neutropenic fever with diffuse multiple cutaneous papular lesions under isavuconazole prophylaxis. A diagnosis of disseminated fusariosis due to *Fusarium fujikoroi* was established. Antifungal therapy had to be adapted multiple times for efficacy and safety issues. Long-term combination therapy with posaconazole and terbinafine efficiently controlled the infection and was well tolerated. # Discussion This case report illustrates three major teaching points: (i) high clinical suspicion based on typical clinical and microbiologic findings is a key factor for the diagnosis of fusariosis; (ii) treatment is challenging due to variable antifungal agent minimal inhibitory concentrations (MICs); and (iii) long-term administration of voriconazole can be associated with multiple, less frequently seen adverse events. # Conclusion Typical skin lesions and positive blood cultures for molds should promptly rise suspicion of fusariosis. Amphotericin-B and voriconazole are the first-line agents for the treatment of fusariosis. Second-line agents such as posaconazole and terbinafine can be used.