The patient has coccidioidomycosis, most likely acquired during her recent trip to Arizona. Coccidioides immitis, a dimorphic fungus, is regularly found in the soil in the southwestern United States, along with parts of Mexico and Central and South America. Even limited exposure in endemic areas can result in inhalation of airborne spores of this pathogen. In most patients, the primary lung infection of coccidiomycosis is asymptomatic; patients who develop clinical disease often report influenza-like illness. Chest imaging studies are nonspecific; findings may be normal in asymptomatic patients or include diffuse infiltrates, nodules, and cavities, sometimes in combination. The endospore-containing spherule detected in the bronchoalveolar lavage specimen shown is characteristic of C. immitis.

Unilateral hilar lymphadenopathy and pleural effusions are observed in approximately one fifth of symptomatic patients. Constitutional and pulmonary symptoms predominate, often beginning weeks after returning from travel. The presence of erythema nodosum lesions on the anterior lower extremities is also fairly common. Severe pulmonary disease and hematogenous dissemination of the organism to skin, bone, joints, peritoneum, and central nervous system occur infrequently, but patients with impaired T-cell–mediated immunity, such as this patient, are at significantly higher risk for more severe disease. Confirmation relies on isolation of the organism from clinical specimens, histologic identification, serologic assays, and DNA probes. Coccidioides infections generally resolve without antifungal therapy, but immunocompromised patients with severe or disseminated infection warrant antifungal therapy. An amphotericin B deoxycholate formulation is recommended in severely ill patients. In all others, fluconazole or itraconazole can be used.

Blastomycosis and histoplasmosis are dimorphic fungi that share clinical features with coccidioidomycosis but are mostly concentrated in the central river valleys and south-central and southeastern United States. Morphologically, the organisms are easily distinguishable from Coccidioides species on clinical specimens.

Mycoplasma pneumoniae is less common in adults and rarely presents as severe pneumonia. A single reactive IgM antibody assay may not be reliable in confirming the diagnosis because both the sensitivity and specificity of this test are suboptimal. Diagnosis is best confirmed by showing a four-fold increase or decrease in paired sera titers or by detecting M. pneumoniae–specific antigens in respiratory secretions using newer immunoassays.