A Reformulated Spherule-Derived Coccidioidin (Spherusol) to Detect Delayed-Type Hypersensitivity in Coccidioidomycosis

The ability of spherule-derived coccidioidin containing 0.4?% phenol and 0.0001?% thimerosal in buffered saline to induce delayed-type hypersensitivity (DTH) was evaluated in four separate studies. The skin test antigen was titrated in 20 adult volunteers with a recent history of pulmonary coccidioidomycosis using intradermal doses of 0.4, 0.8, and 1.6?μg of antigen, based on total dry weight. Based on these data, a dose of 1.27?μg was shown to elicit a mean?±?SEM induration response of 23.5?±?2.3?mm at 48?h, similar to the 23.6-mm response after 48?h of the U. S. Reference coccidioidin last tested approximately 13?years ago. The 1.27?μg dose in 0.1?mL of the spherule-derived antigen (Spherusol) was then examined in three separate groups of adult volunteers to determine the sensitivity and specificity of the product. Fifty-nine of 60 individuals living in a non-endemic area for coccidioidomycosis were skin test negative to Spherusol. Twelve subjects with a recent history of pulmonary histoplasmosis were skin test negative to Spherusol. Finally, 51 of 52 individuals with a recent diagnosis of acute pulmonary coccidioidomycosis were skin test positive to Spherusol. Within this group, prior therapy with fluconazole did not appear to reduce the reactivity to Spherusol. No serious adverse events were observed in the four studies. From these data, Spherusol was found to be safe and has an overall observed sensitivity and specificity of ≥98?% in detecting DTH in coccidioidomycosis.