Clinical Use of Diagnostic Testing

Currently, diagnosis can be established using immunologic assays, culture, or histopathology of tissues involved (1). In mammalian tissues, coccidioidomycosis exists nearly exclusively as a characteristic spherule with endospores (Figure 1). Spherules are approximately 60 – 100 μm in diameter and can contain hundreds of variable sized daughter endospores, each capable of propagating infection. Rarely, hyphae and other atypical forms have been identified in tissues such as lung cavities or bone (2-5). In addition to histopathology, culture of the fungus isolated from a clinical specimen (i.e. bronchoalveolar lavage, CSF culture, tissue culture) confirms the diagnosis (1). Nucleic acid amplification is still being evaluated and developed for use in clinical diagnosis, with several centers using novel primers (6-10). Its potential ability to effectively detect organism in culture negative samples would be welcome, but is as yet unproven. Skin testing to identify the presence of cellular immunity to Coccidioides species is also being redeveloped after a multi-decade absence; the reader is referred to the excellent review by Wack et al (11). Its use is anticipated in both clinical and epidemiologic scenarios and for screening of at risk populations.

Currently, most clinical infections are diagnosed serologically in the setting of a compatible clinical syndrome. Immunodiffusion (ID) for the detection of IgG and IgM specific antibodies is a preferred test for detection of exposure to C. immitis, with high specificity. Complement fixation (CF) tests for IgG specific antibody are most useful in immunocompetent patients; both for diagnosis and long-term disease assessment (12). The CF titer can be useful in monitoring disease activity, and may revert to negative with long-term disease control. Complement fixation titers greater than 1:16 increase the possibility of disseminated disease. Very early in a patient’s infection, serologic results may be negative. Most frequently performed on blood samples, serology may also be performed on cerebrospinal fluid and other samples such as joint or pleural fluid.  Serologic assays are less reliable in immunosuppressed patients with 20-50% of patients testing negative with these methods. In forms of disease with a more benign clinical course, such as patients with isolated pulmonary nodules confirmed by culture or histopathology, serologic testing may often be negative.

Other assays such as latex agglutination and enzyme-linked immunosorbant assay (ELISA) have been used in the endemic region as well, though with mixed results, and often with a high false positive rate (13, 14). Coccidioides galactomannan antigen testing and serum (1→3)-β-D-glucan are available in some reference laboratories and undergoing further evaluation for their role in patient diagnosis or management (15). Identification may also be possible through the use of commercially available rRNA probes (16).

REFERENCES

1. De Pauw B, Walsh TJ, Donnelly JP, et al. Revised definitions of invasive fungal disease from the European Organization for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group (EORTC/MSG) Consensus Group. Clin Infect Dis 2008; 46(12): 1813-21.
2. Schuetz AN, Pisapia D, Yan J, Hoda RS. An atypical morphologic presentation of Coccidioides spp. in fine-needle aspiration of lung. Diagnostic cytopathology 2012; 40(2): 163-7.
3. Kaufman L, Valero G, Padhye AA. Misleading manifestations of Coccidioides immitis in vivo. Journal of clinical microbiology 1998; 36(12): 3721-3.
4. Ke Y, Smith CW, Salaru G, Joho KL, Deen MF. Unusual forms of immature sporulating Coccidioides immitis diagnosed by fine-needle aspiration biopsy. Archives of pathology & laboratory medicine 2006; 130(1): 97-100.
5. Raab SS, Silverman JF, Zimmerman KG. Fine-needle aspiration biopsy of pulmonary coccidiodomycosis. Spectrum of cytologic findings in 73 patients. American journal of clinical pathology 1993; 99(5): 582-7.
6. Mitchell M, Dizon D, Libke R, Peterson M, Slater D, Dhillon A. Development of a real-time PCR Assay for identification of Coccidioides immitis by use of the BD Max system. Journal of clinical microbiology 2015; 53(3): 926-9.
7. Gago S, Buitrago MJ, Clemons KV, Cuenca-Estrella M, Mirels LF, Stevens DA. Development and validation of a quantitative real-time PCR assay for the early diagnosis of coccidioidomycosis. Diagnostic microbiology and infectious disease 2014; 79(2): 214-21.
8. Johnson SM, Simmons KA, Pappagianis D. Amplification of coccidioidal DNA in clinical specimens by PCR. J Clin Microbiol 2004; 42(5): 1982-5.
9. Binnicker MJ, Buckwalter SP, Eisberner JJ, et al. Detection of Coccidioides species in clinical specimens by real-time PCR. Journal of clinical microbiology 2007; 45(1): 173-8.
10. Thompson GR, Sharma S, Bays DJ, et al. Coccidioidomycosis: adenosine deaminase levels, serologic parameters, culture results, and polymerase chain reaction testing in pleural fluid. Chest 2013; 143(3): 776-81.
11. Wack EE, Ampel NM, Sunenshine RH, Galgiani JN. The Return of Delayed-Type Hypersensitivity Skin Testing for Coccidioidomycosis. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America 2015.
12. Pappagianis D. Serologic studies in coccidioidomycosis. Seminars in respiratory infections 2001; 16(4): 242-50.
13. Kuberski T, Herrig J, Pappagianis D. False-positive IgM serology in coccidioidomycosis. Journal of clinical microbiology 2010; 48(6): 2047-9.
14. Blair JE, Mendoza N, Force S, Chang YH, Grys TE. Clinical specificity of the enzyme immunoassay test for coccidioidomycosis varies according to the reason for its performance. Clinical and vaccine immunology : CVI 2013; 20(1): 95-8.
15. Thompson GR, 3rd, Bays DJ, Johnson SM, Cohen SH, Pappagianis D, Finkelman MA. Serum (1->3)-beta-D-glucan measurement in coccidioidomycosis. Journal of clinical microbiology 2012; 50(9): 3060-2.
16. Sandhu GS, Kline BC, Stockman L, Roberts GD. Molecular probes for diagnosis of fungal infections. J Clin Microbiol 1995; 33(11): 2913-9.