The prevalence of cellular immunity to coccidioidomycosis in a highly endemic area

Intradermal skin test reactivity to spherulin and coccidioidin and in vitro spherulin-induced lymphocyte transformation were used to assess cellular immunity in healthy subjects and patients with acute, self-limited coccidioidomycosis (cocci). The objectives of this study were to evaluate the relative sensitivities of the two assays in assessing cellular immunity to cocci, especially in long-term residents of an endemic area (Tucson) and, based on data from both assays, determine the prevalence of detectable cellular immunity to cocci in this highly endemic area. The lymphocyte transformation assay appeared to be more sensitive than the skin test in assessing long-term immune status, and the prevalence of detectable immunity to cocci in this highly endemic area was only 75% in long-term residents. This is much lower than previous prevalence estimates (90%) in other endemic areas. The absence of a demonstrable cell-mediated immunity may indicate either no prior antigen exposure (infection) or previous remote exposure with a diminished immune response (no reexposure to boost immunity). A possible explanation for the lower prevalence of immunity to cocci in this endemic area may relate to the increased urbanization of the Southwest in the past several years. Therefore, the clinical suspicion of acute cocci should not be restricted to recent arrivals to endemic areas.