Coccidioidomycosis is caused by the two species of the dimorphic soil-dwelling fungus Coccidioides: C. immitis and C. posadasii. These organisms exist as branching, filamentous molds.

• Coccidioidomycosis is confined to the Western Hemisphere between the latitudes of 40°N and 40°S. The disease is highly endemic in California, Arizona, and other areas of the southwestern United States, with ~43 cases per 100,000 residents in 2011; northern Mexico and localized regions in Central and South America also account for cases of infection.
• Direct exposure to soil harboring Coccidioides increases risk, but infection, which results from inhalation of airborne arthroconidia, can occur without overt soil exposure and may be related to other climatic factors (e.g., periods of dryness after rainy seasons).