Coccidioides is a fungus that causes coccidioidomycosis . Coccidioidomycosis is common in the San Joaquin Valley of California and certain other areas in the Southwestern U.S. Symptoms resemble pneumonia or pulmonary tuberculosis . There may be small, red, inflamed areas on the skin. This test detects exposure to this fungus. Coccidioidin and spherulin are two different antigens and are both used. Spherulin may be a more sensitive test than coccidioidin.