Chapter 298

Coccidioidomycosis is the infection caused by the dimorphic fungus Coccidioides immitis. The history of the identification of this organism and the clinical study of the infections caused by this agent have been the subject of a number of comprehensive reviews.1-2 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.

The life cycle of C immitis is complex (reviewed in Parish and Blair4) 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, 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.

### Epidemiology

In general, C immitis appears 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 organism 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—ecological conditions that favor C immitis. The organism is 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.5

### Clinical Manifestations

#### Pulmonary Infection

The primary portal of entry in most patients is the lung, although the organism may enter through the skin. Accordingly, signs and symptoms of respiratory tract infection represent the major clinical manifestations of acute coccidioidomycosis in most patients.6 Pulmonary coccidioidomycosis occurs in 95% of all cases. The majority of individuals with acute coccidioidomycosis will have either asymptomatic infection or mild upper respiratory tract symptoms. Approximately ...

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