Coccidioidomycosis is the infection caused by the dimorphic fungi Coccidioides immitis or Coccidioides posadasii. Although it was initially believed that coccidioidomycosis was an invariably lethal infection, by the mid-1930s, it was recognized that the organism was in fact responsible for a very common, acute, and generally self-limited disease that was known as the San Joaquin Valley fever. In regions where coccidioidomycosis is endemic, Valley fever continues to be an important public health problem. In addition, coccidioidomycosis has emerged in recent years as an important cause of disease in immunocompromised patients, particularly those with human immunodeficiency virus (HIV) infection.
PATHOGENESIS AND EPIDEMIOLOGY
The life cycle of Coccidioides species is complex and demonstrates 2 distinct phases: a saprophytic (vegetative) phase and a parasitic phase. In soil, the organism grows as a mycelium, with branching septated hyphae. As they mature, the mycelia develop rectangular spores (arthroconidia); at this stage, the hyphae become very fragile, and arthroconidia easily become airborne. When inhaled into the lungs (it appears that a single spore can cause disease), the arthroconidia begin the parasitic phase, and spherules form. Spherules are round, double-walled structures that reproduce by formation of spherical internal spores, termed endospores. A single spherule may produce thousands of endospores, and as the spherule ruptures, each endospore may in turn develop into a new spherule, perpetuating the parasitic phase in the tissues. An intense inflammatory response ensues, and the infection stays limited to the lungs and hilar nodes in the majority of patients. Extrapulmonary dissemination can occur, and cutaneous disease has been described after puncture of the skin with a contaminated object.
In general, Coccidioides species appear to be confined to the Western Hemisphere. The endemic areas lie in the southwestern United States, encompassing west Texas, New Mexico, Arizona, and California. The organisms can also be found in northwestern Mexico and a few small areas of Central and South America. These endemic areas have arid climates, hot summers, few winter freezes, low altitude, and alkaline soil—ecologic conditions that favor human infection with Coccidioides. The organisms are drought resistant, and periodic increases in cases are observed when prolonged drought is followed by periods of heavy rain. Arthroconidia may become airborne after windstorms or disruption of soil by farming or construction work. Since infection requires that arthroconidia be inhaled, person-to-person transmission does not play a role in acquisition of coccidioidomycosis. Hospitalizations for coccidioidomycosis are common, particularly in endemic areas. County of residence, older age, black race, male sex, intercurrent HIV infection, and pregnancy are all risk factors strongly associated with an increased risk for hospitalization.
The primary portal of entry in most patients is the lung. Accordingly, signs and symptoms of respiratory tract infection represent the major clinical manifestations of acute coccidioidomycosis in most patients. Pulmonary coccidioidomycosis occurs in 95% of all cases. The ...