Interpretive Handbook

Coccidioidomycosis (Valley fever, San Joaquin Valley fever) is a fungal infection found in the southwestern United States, Central America, and South America. It is acquired by inhalation of arthroconidia of Coccidioides immitis.  Usually, it is a mild, self-limiting pulmonary infection, often leaving a coin-like lesion. Less commonly, chronic pneumonia may persist or progress to fibronodular, cavitary disease.  A rash often develops within a day or 2, followed by erythema nodosum or multiforme and accompanying arthralgias. About 2 weeks after exposure, symptomatic patients develop fever, cough, malaise, and anorexia; chest pain is often severe.  Coccidioidomycosis may disseminate beyond the lungs to involve multiple organs including the meninges.

IgG antibody is detected by the complement-fixation tests. Precipitating antibodies (IgM and IgG) are detected by immunodiffusion (ID). They are rarely found in cerebrospinal fluid (CSF); however, their presence is associated with meningitis. Chronic coccidioidal pulmonary cavities are often accompanied by IgG and IgM precipitating antibodies.

Diagnosing coccidioidomycosis

Serologic testing for coccidioidomycosis should be considered when patients exhibit symptoms of pulmonary or meningeal infection and have lived or traveled in areas where Coccidioides immitis is endemic. Any history of exposure to the organism or travel cannot be overemphasized when a diagnosis of coccidioidomycosis is being considered.

Complement Fixation (CF):

Titers of > or =1:2 may suggest active disease; however, titers may persist for months after infection has resolved. Increasing CF titers in serial specimens are diagnostic of active disease.

Immunodiffusion (ID):

The presence of IgM antibody may be detectable within 2 weeks after the onset of symptoms; however, antibody may be detected longer than 6 months after infection.

The presence of IgG antibody parallels the CF antibody and may suggest an active or a recent asymptomatic infection with Coccidioides immitis; however, antibody may persist after the infection has resolved.

An equivocal result (a band of nonidentity) cannot be interpreted as significant for a specific diagnosis. However, this may be an indication that a patient should be followed serologically.

Over 90% of primary symptomatic cases will be detected by combined ID and CF testing.

Antibodies (both IgM and IgG) may be present after the infection has resolved.

COMPLEMENT FIXATION

Negative

If positive, results are titered.

IMMUNODIFFUSION

Negative

Results are reported as positive, negative, or equivocal.

Larone D, Mitchell T, Walsh T: Histoplasma, blastomyces, coccidioides, and other dimorphic fungi causing systemic mycoses. In Manual of Clinical Microbiology. 7th edition. Edited by PR Murray, EJ Baron, MA Pfaller, et al: Washington, DC, American Society for Microbiology, 1999, pp 1260-1261