Probable false positive coccidioidal serologic results in patients with cystic fibrosis

Coccidioidomycosis is an acquired fungal infection that afflicts primarily the respiratory tract. Cystic fibrosis patients who are being treated with glucocorticoids and immunosuppressed organ recipients may be at risk for infection with Coccidiodes immitis or reactivation of latent infection. The diagnosis is best made by demonstration of the organism in pathologic specimens or by culture. Serologic screening is another method that is reliable in most patients. We studied 98 patients who had serologic screening for Coccidiodes immitis performed as part of their evaluation for lung transplantation. This study revealed that approximately 15% of the cystic fibrosis patients screened had putative coccidioidal IgM, in the absence of an IgG response. None of the patients studied had a positive fungal culture for the organism. None of the non-cystic fibrosis patients screened had detectable coccidioidal IgG or IgM. We hypothesize that cystic fibrosis patients may have hyperimmune sera which interferes with serologic screening tests. We would recommend repeat serologic testing and attempts to identify the organism in tissue or by culture to confirm the diagnosis in these patients.