Clinical Specificity of the Enzyme Immunoassay Test for Coccidioidomycosis Varies According to the Reason for Its Performance

Abstract

The diagnosis of coccidioidomycosis relies heavily on serologic test results in addition to clinical history, physical examination, and radiographic findings. Use of the enzyme immunoassay (EIA) has increased because it is rapidly performed and does not require referral to a reference laboratory, as do complement fixation and immunodiffusion tests. However, interpretation of immunoglobulin M (IgM) reactivity by EIA in the absence of immunoglobulin G (IgG) reactivity has been problematic. We conducted a retrospective medical record review of all patients with such IgM reactivity at our institution to identify situations where the finding was more likely to be clinically specific for coccidioidal infection. From 1 January 2004 through 31 December 2008, a total of 1,117 patients had positive EIA coccidioidal serology or EIA IgM-only reactivity; of these, 102 patients (9%) had EIA IgM-only reactivity. Among the 102 patients with EIA IgM-only reactivity, 60 were tested to evaluate symptomatic illness, 13 for follow-up of previously abnormal serology, and 29 for screening purposes. Of the 102 patients, 80 (78%) had positive serologic findings by other methods or had positive culture or histology. Fifty-four (90%) of the 60 patients whose serology was performed to evaluate symptomatic illness had coccidioidal infection, whereas 13 (45%) of 29 patients whose serology was performed for screening purposes had coccidioidal infection. Of the 102 patients with isolated IgM reactivity by EIA, 12 later seroconverted to IgG and IgM reactivity. The use of EIA for screening in 29 asymptomatic persons was associated with unconfirmable results in 13 (45%). Although the majority of patients in our study with isolated IgM reactivity by EIA had probable or confirmed coccidioidomycosis, this result must be interpreted with caution for asymptomatic patients.

Evaluation of the Specificity of Two Enzyme Immunoassays for Coccidioidomycosis by Using Sera from a Region of Endemicity and a Region of Nonendemicity

“…Some research groups have reported elevated rates of false positivity, especially among individuals with IgM-only positive results (3,10). Others have reported that the predictive value of such tests depends on the prior probability of CM for a given patient (13). The current study addresses this question by IgG 44 39 5 IgM 29 14 2 IgG and IgM 7 3 1 Total 80 56 8 Puerto Rico IgG 2 4 0 IgM 18 8 2 IgG and IgM 0 0 0 Total 20 12 2 assessing EIA results from individuals living outside a region of endemicity (Puerto Rico), who are not expected to have been exposed to Coccidioides spp., and comparing the results with those from individuals living in a region of endemicity (Arizona).…”

Diagnostic Immunology

“…This relatively common finding (~ 10 % of positive tests) has been the subject of several recent publications with quite discrepant conclusions (false-positive rate range 0-82 %) [73]. In particular, one should question the validity of an isolated positive IgM test in an asymptomatic patient or one without classic symptoms [74]. In general, EIAs should be confirmed with ID and/or CF.…”

Coccidioidomycosis: epidemiology

“…An enhanced surveillance study suggests that the use of laboratory-only criteria for case reporting, including a single positive EIA test, accurately reflects the burden of disease in Arizona 110. Other reports show that EIA testing has a high false-positivity rate111 and more recent evidence has suggested the performance characteristics of EIA testing varies among different patient groups 112…”