L. Joseph Wheat, M.D.
I’m often contacted for advice on diagnosis of the endemic mycoses. Many physicians are unaware of these tests and publications describing their use for diagnosis.
For example, some believe the Histoplasma antigen test is performed only on urine. Others believe that antigen testing on serum is unnecessary. In fact, nearly half of the cases of acute pulmonary histoplasmosis would have been missed if only urine were tested (sensitivity 83% for combined serum and urine testing; 45% with urine alone) (1). At least 5% of disseminated cases would be missed if only urine were tested (unpublished). Both urine and serum should be tested for maximum sensitivity. Antigen testing of CSF is the most sensitive method for diagnosis of Histoplasma meningitis (2;3). Detection of antigen in the bronchoalveolar lavage fluid (BAL) is useful for diagnosing pulmonary histoplasmosis (4).
Some also believe that Histoplasma antibody detection is not useful for diagnosis because most individuals from endemic areas have had histoplasmosis, and antibody tests would not differentiate active infection from previous exposure. Studies in Indianapolis, where 50% of residents are histoplasmin skin test positive, reported positive antibody results by immunodiffusion (ID) in 0.5% and by complement fixation (CF) in 5% (5). Skin test reactivity persists for life in most individuals while antibodies clear over a few years.
The newly described MVD IgG and IgM enzyme immunoassay (EIA), combined with antigen detection, improves the sensitivity for diagnosis of acute pulmonary histoplasmosis over antigen and antibody detection by ID or CF (6). The assay is quantitative and was useful for detecting seroconversion in these cases. Similarly, sensitivity for diagnosing Histoplasma meningitis by testing CSF increased from 78% to 98% by combining antigen and IgG/IgM antibody testing (2). Both antigen and MVD antibody EIA should be tested for maximum sensitivity.
Many are unaware of the MVD Coccidioides antigen detection assay or believe that its sensitivity is low. The limit of detection is the same in our Coccidioides and Histoplasma antigen assays, <0.2ng/mL. The clinical sensitivity in disseminated cases is somewhat lower, about 70% in coccidioidomycosis (7;8) and 90% in histoplasmosis (9). The reason for the lower clinical sensitivity in coccidioidomycosis is the lower fungal burden. For example, the lungs, liver, spleen, bone marrow, other tissues are often involved in disseminated histoplasmosis and fungemia is common. Isolated sites of dissemination to skin, bone, or CNS are more common in coccidioidomycosis and fungemia is rare. Larger unpublished studies indicate the sensitivity was 80% in disseminated cases, most of whom were immunocompromised, if both urine and serum were tested. Antigen detection in CSF is the most sensitive method (91%) for diagnosing Coccidioides meningitis (10).
The MVD Coccidioides IgG and IgM antibody EIA was introduced in 2017 (11). MVD EIA is more sensitive than ID or CF and is not impacted by immunocompromise (11). The assay is quantitative and useful for monitoring changes in antibody concentrations (unpublished). Sensitivity in CSF in Coccidioides meningitis is 73% (unpublished).
The MVD Blastomyces antigen EIA is the most sensitive method for diagnosing disseminated and pulmonary blastomycosis (12). Antigen also may be detected in CSF (13) in patients with meningitis and BAL fluid in patients with pneumonia (4). We have developed an IgG Blastomyces antibody EIA that is more sensitive than immunodiffusion (14). Combined antigen and MVD EIA antibody testing increased the sensitivity from 88% to 98%. This IgG test is available as “research use only (RUO)” pending completion of validation and requires preapproval by the laboratory director. The MVD Blastomyces antibody EIA is projected to be validated and offered routinely in mid-2019.
(1) Swartzentruber S, Rhodes L, Kurkjian K, et al. Diagnosis of acute pulmonary histoplasmosis by antigen detection. Clin Infect Dis 2009 Dec 15;49(12):1878-82.
(2) Bloch KC, Myint T, Raymond-Guillen L, et al. Improvement in Diagnosis of Histoplasma Meningitis by Combined Testing for Histoplasma Antigen and Immunoglobulin G and Immunoglobulin M Anti-Histoplasma Antibody in Cerebrospinal Fluid. Clin Infect Dis 2018 Jan 6;66(1):89-94.
(3) Wheat J, Myint T, Guo Y, et al. Central nervous system histoplasmosis: Multicenter retrospective study on clinical features, diagnostic approach and outcome of treatment. Medicine (Baltimore) 2018 Mar;97(13):e0245.
(4) Hage CA, Davis TE, Fuller D, et al. Diagnosis of Histoplasmosis by Antigen Detection in BAL Fluid. Chest 2010 Mar;137(3):623-8.
(5) Wheat J, French ML, Kohler RB, et al. The diagnostic laboratory tests for histoplasmosis: analysis of experience in a large urban outbreak. Ann Intern Med 1982 Nov;97(5):680-5.
(6) Richer SM, Smedema ML, Durkin MM, et al. Improved Diagnosis of Acute Pulmonary Histoplasmosis by Combining Antigen and Antibody Detection. Clin Infect Dis 2016 Apr 1;62(7):896-902.
(7) Durkin M, Connolly P, Kuberski T, et al. Diagnosis of Coccidioidomycosis with Use of the Coccidioides Antigen Enzyme Immunoassay. Clin Infect Dis 2008 Oct 15;47(8):e69-e73.
(8) Durkin M, Estok L, Hospenthal D, et al. Detection of coccidioides antigenemia following dissociation of immune complexes. Clin Vaccine Immunol 2009 Oct;16(10):1453-6.
(9) Hage CA, Ribes JA, Wengenack NL, et al. A multicenter evaluation of tests for diagnosis of histoplasmosis. Clin Infect Dis 2011 Sep;53(5):448-54.
(10) Kassis C, Zaidi S, Kuberski T, et al. Role of Coccidioides Antigen Testing in the Cerebrospinal Fluid for the Diagnosis of Coccidioidal Meningitis. Clin Infect Dis 2015 Nov 15;61(10):1521-6.
(11) Malo J, Holbrook E, Zangeneh T, et al. Enhanced Antibody Detection and Diagnosis of Coccidioidomycosis with the MiraVista IgG and IgM Detection Enzyme Immunoassay. J Clin Microbiol 2017 Mar;55(3):893-901.
(12) Connolly P, Hage CA, Bariola JR, et al. Blastomyces dermatitidis Antigen Detection by Quantitative Enzyme Immunoassay. Clin Vaccine Immunol 2012 Jan;19(1):53-6.
(13) Walkty A, Keynan Y, Karlowsky J, Dhaliwal P, Embil J. Central nervous system blastomycosis diagnosed using the MVista(R) Blastomyces quantitative antigen enzyme immunoassay test on cerebrospinal fluid: A case report and review of the literature. Diagn Microbiol Infect Dis 2018 Feb;90(2):102-4.
(14) Richer SM, Smedema ML, Durkin MM, et al. Development of a Highly Sensitive and Specific Blastomycosis Antibody Enzyme Immunoassay Using Blastomyces dermatitidis Surface Protein BAD-1. Clin Vaccine Immunol 2014 Feb;21(2):143-6.
(15) Connolly PA, Durkin MM, LeMonte AM, Hackett EJ, Wheat LJ. Detection of histoplasma antigen by a quantitative enzyme immunoassay. Clin Vaccine Immunol 2007 Dec;14(12):1587-91.