Coccidioides (spherulin) skin testing in patients with pulmonary coccidioidomycosis in an endemic region†.

Coccidioidomycosis is an endemic fungal infection of the desert southwestern United States. Intact cellular immunity is critical to the control of this infection. A recently released reformulated spherulin antigen (Spherusol; Nielsen BioSciences, Inc.) was approved to detect delayed-type hypersensitivity, which implies the presence of cellular immunity, to Coccidioides species. We aimed to summarize our experience with this test in patients with primary pulmonary coccidioidomycosis. We retrospectively reviewed clinical data for all patients with primary pulmonary coccidioidomycosis who had a Coccidioides (spherulin) skin test (CST) placed at our institution between January 1, 2015, and August 31, 2017. During the study period, 172 patients had a CST placed, and 122 met our inclusion criteria for proven or probable pulmonary coccidioidomycosis. Of these 122, 88 (72.1%) had a positive CST result and 34 (27.9%) had a negative result. In the positive CST group, 74 of the 79 treated patients (93.7%) had antifungal treatment stopped, 1 of whom (1.4%) had relapsed infection. In contrast, 27 of the 33 treated patients in the negative CST group (81.8%) had their antifungal treatment stopped, and none had a relapse. Seven patients overall (5.7%), all of whom had a positive CST, experienced mild local adverse reactions to the CST. Although previous controlled studies of CST showed sensitivity and specificity greater than 98%, our real-world experience with the CST showed lower rates of positivity. Negative CST results did not predict relapse with antifungal agent withdrawal.