Coccidioidomycosis (valley fever, San Joaquin fever) is caused by the dimorphic fungus Coccidioides immitis. This fungus grows in the soil and produces spores (arthroconidia), which are carried by air currents and inhaled by humans and lower animals. In the united States, Coccidioidomycosis is endemic to California, Arizona, New Mexico, parts of Nevada and Utah, and southwestern Texas.

The population of the endemic areas is estimated to be about 20,000,000 (Chin, personal communication, 1983; Pappagianis, personal communication, 1983), but temporary visitors to these areas also may develop the disease. Individuals in occupations that involve working with the soil (e.g., agriculture, construction, and oil drilling) appear to be at increased risk (Chin, personal communication, 1983; Cox, 1983; Pappagianis, personal communication, 1983). Morbidity and mortality rates also are higher among certain racial and ethnic groups: black, Asian (especially Filipino), and Mexican males are at greater risk of disseminated disease than white males, for example (Pappagianis, 1980). The disease affects all age groups; the highest incidence is in males over the age of 25.

Less than half of those who become infected develop clinical signs of disease. The primary lesion is usually pulmonary. In those who become ill, clinical symptoms of fever, malaise, cough, and chest pain follow an incubation period of 7 to 28 days (typically 10 to 16 days). Night sweats and anorexia may occur also. The disease is usually self-limited, particularly in adults. A few individuals may develop residual cavitary disease, and sometimes nodules or pulmonary abscesses. The pulmonary cavities usually heal spontaneously. Chronic progressive pulmonary disease, resembling histoplasmosis or tuberculosis, occurs in a small number of patients.

Allergic manifestations also appear in some cases. Erythema nodosum or erythema multiforme may develop a few days or a few weeks