Comparison of Indirect Fungal Diagnostic Tests in Patients With Proven Histoplasmosis

Histoplasmosis 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 are typically performed to assist with diagnostic workup, though cross-reaction can lead to difficulty in interpreting results. We aimed to compare indirect fungal diagnostic tests and evaluate prevalence of positive antigen testing for non-Histoplasma fungal pathogens in patients with proven histoplasmosis.

We performed a single-center retrospective review of adult patients with proven histoplasmosis diagnosed by fungal culture and/or cytology from January 2010 to March 2018. Patient demographics, clinical characteristics, and results of fungal antigen testing for Histoplasma, Blastomyces, Aspergillus, Cryptococcus, and (1→3)-β-D-glucan were evaluated. Two different urine Histoplasma antigen assays were used during the study period.

Fifty-seven of 182 (31.3%) patients reviewed had proven histoplasmosis and presented with acute pulmonary (n = 10), chronic pulmonary (n = 7), and disseminated (n = 40) disease. Forty-one (72%) of these patients were immunosuppressed. Urine Blastomyces antigen (93%) and serum (1→3)-β-D-glucan (88%) were commonly positive in patients with histoplasmosis, whereas Aspergillus antigen was detected in 50% of patients and Cryptococcus antigenemia was rare (5%). In patients with disseminated disease, the MiraVista urine Histoplasma antigen assay had higher sensitivity than the Viracor urine Histoplasma antigen assay (86% vs 50%, respectively; P = .019).

Noninvasive fungal antigen assays are helpful diagnostic tools; however, given their low specificity, clinicians must be aware of the various clinical presentations of invasive fungal infections and be aware of the limitations of these tests.