Role of Blastomyces BAD-1 IgG Enzyme Immunoassay (EIA) for the diagnosis of blastomycosis in persons residing in an endemic area

Blastomyces species complex causes infection in persons with intact and impaired immune defenses. The diagnosis of blastomycosis is challenging because it mimics infectious and non-infectious diseases. Blastomyces adhesin-1 (BAD-1) protein is a major virulence factor in B. dermatitidis and B. gilchristii and induces a humoral immune response during infection. The goal of this retrospective, case-control study conducted at the University of Wisconsin-Madison is to investigate the test characteristics of the newly developed second generation BAD-1 IgG Enzyme Immunoassay (EIA) antibody test for the diagnosis of blastomycosis. The study was performed in an endemic area in a diverse patient population including persons with underlying immunocompromise. Thirty-six case patients with proven or probable blastomycosis were compared to 370 controls. Serum BAD-1 IgG was positive in 50% of the case patients and in 9.7% of the controls, which resulted in a sensitivity of 50% and specificity of 90.2%. The highest sensitivity (80%) occurred in non-immunocompromised persons with chronic blastomycosis and the lowest sensitivity occurred in those with acute blastomycosis (35.0%) or immunocompromise (37.5%). Sensitivity was not influenced by dissemination or severity of disease. In conclusion, this study demonstrates that the BAD-1 IgG EIA can serve as adjunctive test for the diagnosis of blastomycosis in select patient populations living in regions endemic for blastomycosis.