271. Fungal Diagnostic Studies in Histoplasmosis

BACKGROUND: Histoplasmosis (histo) is a common cause of invasive fungal infection in endemic regions and accurate diagnosis is difficult without direct tissue culture or pathology. Indirect fungal antigen testing for various fungal pathogens is typically performed to assist with diagnostic workup though cross-reaction can lead to difficulty interpreting results. We aimed to evaluate the prevalence of positive antigen testing for non-Histoplasma fungal pathogens in patients with proven invasive histo. METHODS: We performed a retrospective review of adult patients with proven invasive histo from 2010–2018 at our institution. For inclusion purposes, histo was confirmed by either fungal culture and/or cytology. Patient demographics, clinical characteristics and results of fungal antigen testing for Histoplasma, Blastomyces, Aspergillus, Cryptococcus and β-d-glucan were evaluated. Two different urine Histoplasma antigen assays were used during the study period. RESULTS: 57 (31%) of 182 patients diagnosed with histo during the study period had culture or cytology evidence of disease and were included in all further analysis. Thirty-two (56%) of these patients were male, 35 (61.4%) were Caucasian and the mean age was 50.1 years. HIV (20; 35%) and being on immunosuppressive medications (21, 37%) were common in this population. The majority of cases were classified as disseminated histo (40, 70%) followed by acute pulmonary (10; 18%) and chronic pulmonary (7, 12%) disease. Results of fungal antigen testing are documented in the table. Chi-squared analysis was performed. CONCLUSION: There is a frequent cross reaction of non-Histoplasma fungal tests in patients with histo. In our review, there was a high rate of cross reaction with Blastomyces antigen, which can be confusing in regions where both pathogens coexist. Elevation of β-d-glucan was high in these patients. Urine Histoplasma antigen sensitivity was higher with MiraVista testing for disseminated disease in our review. While noninvasive fungal tests are helpful in diagnosis of these infrequent infections, clinicians must still maintain knowledge of the clinical differences between these fungal pathogens and be aware of the limitations of these tests. A prospective study is needed to better define differences between individual Histoplasma tests. [Image: see text] DISCLOSURES: All authors: No reported disclosures.