Useful Roles and Limitations for the Coccidioides Antigen Detection Enzyme Immunoassay.

To the Editor—Fierer’s editorial, “One Small Step,” presented useful information on the roles and limitations for the Coccidioides antigen detection enzyme immunoassay [1]. He noted that the antigen test performed best in immunocompromised patients living with human immunodeficiency virus (HIV)/AIDS (PLHIV). PLHIV comprised 39.5% of cases, potentially biasing our assessment toward a higher sensitivity (57%) for antigen detection. A prospective study is planned at an institution with PLHIV to address this concern.

He indicated that assessment of sensitivity in probable cases was biased by inclusion of positive antigen results as a basis for determination of sensitivity. We have analyzed 34 probable cases diagnosed using antibody testing that excluded antigen results, of which antigen was detected in 38.2%.

He commented that antigen detection could identify infection sooner than antibody detection. The patients evaluated in the VHMC retrospective study presented late, and serial testing was not performed. We have planned prospective studies at 2 institutions in highly endemic areas to address this hypothesis.

We agree with Fierer that antigen detection is less sensitive than antibody detection; however, antigen alone was detected in 11.3% of cases, in which delayed or missed diagnoses may have serious consequences [3]. We thank Fierer for his insightful and helpful comments that we plan to evaluate in prospective clinical trials.