Enzyme Immunoassay (EIA) Tests

Coccidioidomycosis presents a diagnostic challenge to the physician and laboratorian. The manifestations of most early coccidioidal infections overlap substantially with those of other respiratory infections. In addition, culturally and histologically the organisms can be difficult to demonstrate, even after repeated attempts. Therefore, specific laboratory testing is usually required to establish a diagnosis of coccidioidomycosis. Serologic tests have served for several decades as aids in the diagnosis and management of coccidioidomycosis. Complement fixation (CF), immunodiffusion (ID) and latex agglutination (LA) have been the most commonly used serologic methods. The CF assay is sensitive; however, its performance is complex and labor intensive, and the CF assay exhibits low specificity due to cross-reactive antibodies recognizing carbohydrate moieties common to several fungi. The ID assay is more specific, but less sensitive than the CF assay. In addition, the ID assay takes 48 hours to perform and requires highly skilled personnel to properly interpret results. The LA assay is sensitive and rapid, but lacks specificity. However, the OMEGA Coccidioides Antibody EIA is a sensitive, specific, and rapid test for the qualitative detection of IgM and IgG antibodies against antigens from Coccidioides.

Complement Fixation (CF) Tests for Coccidioidomycosis

Coccidioidomycosis: A CF titer of 1:2 or greater may be significant and is presumptive evidence of current or recent past infection. Titers greater than 1:16 are usually associated with severe disease. Patients with a limited number of extrapulmonary lesions (eg. bone, skin, or central nervous system) may have titers below 1:16.  Fourfold or greater decreases in titer on serial specimens usually indicate improvement. In chronic residual pulmonary disease, a significant number of patients (>30%) may have negative CF tests.

Antibody demonstrable by the CF test usually develops within 4 to 6 weeks after exposure and reaches a maximum response within 2 to 3 months. For those patients with positive reactions, the test is of diagnostic and prognostic values. Low titers are generally associated with mild, localized disease or stable residual lesions, while high or rising titers are usually associated with progressive or severe disease. A negative test does not exclude the possibility of active coccidioidomycosis. For more complete serologic testing, immunodiffusion and latex agglutination tests should be performed in parallel with the CF tests.

Immunodiffusion (ID) Tests

C. immitis (California isolates) and C. posadasii (non-California isolates) are found predominately in the southwestern United States, and Central and South America, but modern transportation has increased the likelihood of infection for individuals visiting the region. Serologic diagnosis of coccidioidomycosis is generally based on the detection by ID and complement fixation (CF) of antibodies to two Coccidioides antigens, IDTP and IDCF. IDTP antibodies have been associated with primary acute disease and are thought to belong mostly to the IgM class. IDCF antibodies persist during the chronic, disseminated phase of the disease and have been described as primarily IgG antibodies. However, IDTP and IDCF antibodies may not be detected in immunocompromised or immunosuppressed patients. The CF test, when run concurrently with the ID test, is the best combination for making a presumptive diagnosis of coccidioidomycosis. The semi-quantitative IDCF test titer is not identical to the CF test titer, but the trends are comparable and have prognostic value.

Latex Agglutination (LA) Tests

C. immitis (California isolates) and C. posadasii (non-California isolates) are somewhat localized in the southwestern United States and Central and South America, but modern transportation has increased the likelihood of infection for individuals visiting the region. The LA-COCCIDIOIDES test is a sensitive and rapid screening test, but it has a false-positive rate, so confirmation of the results of latex agglutination (LA) by immunodiffusion (ID) and/or complement fixation (CF) is recommended.

Immunodiffusion Plates

Enzyme Immunoassay (EIA)

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Complement Fixation (CF)

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Immunodiffusion (ID)

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Latex Agglutination (LA)

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