419. Diagnostic Performance of Immunohistochemistry Test to Differentiate Aspergillosis from Mucormycosis With Formalin-Fixed Tissue Specimens

Background Distinguishing aspergillosis from mucormycosis is clinically important as different antifungal agents are required. However, the sensitivity of fungal culture is suboptimal and histomorphologic diagnosis is not always accurate due to morphologic similarities. We investigated the diagnostic performance of immunohistochemistry (IHC) test for diagnosis of aspergillosis and mucormycosis. Methods Patients who met the criteria for mycologically proven aspergillosis or mucormycosis and in whom formalin-fixed, paraffin-embedded tissues were available were enrolled at a tertiary hospital from January 1992 to October 2017. Mycologically proven invasive fungal infections were defined as there were the histologic evidence of tissue invasion of hyphae and the recovery of Aspergillus species or agents of mucormycosis (Rhizopus spp., Cunninghamella spp., Apophysomycesspp., Saksenaea spp., Absidia spp., Mucor spp.) by culture from sterile specimens. Anti-Aspergillus mouse monoclonal antibody (1:50; clone WF-AF-1; LSBio, WA, USA) and anti-Rhizopus arrhizus mouse monoclonal antibody (1:100; clone WSSA-RA-1; LSBio, WA, USA) were used for IHC test, and we evaluated the diagnostic performance of IHC test using sensitivity and specificity. Results A total of 32 invasive fungal infection including 12 proven mucormycosis and 20 proven aspergillosis were analyzed. The fungal species from sterile sites and diagnostic performance of IHC test for these 30 patients were shown in Table 1. Conclusion The IHC test seems to be useful in compensating the limitations of histomorphologic diagnosis in distinguishing between aspergillosis and mucormycosis. Keywords. Aspergillosis; Mucormycosis; Histomorphology; Immunohistochemistry Table 1: Diagnostic Performance of Mucormycosis and Aspergillosis Immunohistochemistry Tests in Proven Mucormycosis and Proven Aspergillosis IHC Test Result Proven Mucormycosis,No. of Cases (n = 12) Proven Aspergillosis,No. of Cases (n = 20) Diagnostic Performance% (95% CI) Mucormycosis Positive 12 0 Sensitivity: 100(70–100) Negative 0 0 Specificity: 100 (80–100) Aspergillosis Positive 0 18 Sensitivity: 90(67–98) Negative 0 2 Specificity: 100(70–100) Abbreviations: CI, confidence interval; IHC, immunohistochemistry. Disclosures S. H. Kim, the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI): Investigator, Grant recipient.