Background

Coccidioidomycosis, first described more than a century ago by Alejandro Posadas, is a disease of protean manifestations primarily endemic within ecologic zones of the Western Hemisphere characterized as the Lower Sonoran Life Zone with hot summers, few winter freezes, and annual rainfall of 10 to 50 cm. This includes areas in the southwestern United States (California, Arizona, western Texas, and highly localized areas of New Mexico, Nevada, and Utah), northern Mexico, and possibly Washington State, as well as scattered foci in Central and South America. Within these areas the incidence of coccidioidomycosis may vary significantly due to soil and climatic conditions that affect fungal and airborne dispersal, together with human behavior that increases exposure. There has been a marked increase in incidence in Arizona and California in recent years. Coccidioides, the etiologic agent of the infection, is a dimorphic fungus that grows in its soil reservoir in the mycelial (mold) phase. Under appropriate conditions, arthroconidia, the infectious spore form, disarticulate from mycelia and are carried airborne and inhaled, reaching the alveoli of the host. There the organism converts to the spherule phase, which reproduces by endosporulation with the subsequent rupture of the spherule releasing as many as 100 endospores, which subsequently, in turn, mature into spherules. Local control of the infection within the lung is the rule, but in some cases a chronic pulmonary infection may result or infection may spread within the thorax and/or distantly, via the lymphatics and bloodstream. Disseminated infection, especially when it involves the meninges, carries with it considerable potential for morbidity and mortality.

Coccidioides consists of two individual species, each with its own geographic distribution: Coccidioides immitis (found primarily in California) and Coccidioides posadasii (Arizona, Texas, and Mexico and areas of Central and South America). There are no substantive phenotypic differences between the species and the differentiation of one from the other is not routinely performed in the clinical laboratory. Similarly, no specific diagnostic, therapeutic, or prognostic ramifications have been attributed to the individual species.