Evaluation of the exoantigen test for identification of Histoplasma species and Coccidioides immitis cultures

Recently it was demonstrated that certain fungal pathogens could be rapidly and accurately identified on the basis of their exoantigens. Mycelial-form cultures of the Histoplasma species consistently appear to produce either H or M antigens, or both, whereas cultures of Coccidioides immitis produce tube precipitinogen, heat-labile precipitinogen, or heat-labile F antigens. Three laboratories each evaluated 48 cultures by the exoantigen procedure for the identification of Histoplasma spp. and C. immitis. One hundred forty-four cultures were tested, and 143 (99.3%) were correctly identified as Histoplasma spp. or C. immitis, or neither. The simple and rapid exoantigen test appears to be a sensitive and specific method for identification of these fungi.