Blastomyces Antigen Detection for Diagnosis and Management of Blastomycosis

Abstract

cBlastomyces spp. antigen testing was evaluated over a 10-year period in an area where blastomycosis is endemic. Antigen testing was less sensitive than previously reported, but serial urine testing was useful in monitoring disease resolution or progression. Culture and cytopathology remain the gold standard for diagnosis and exclusion of this infection. Blastomycosis is a serious and potentially fatal fungal infection. Blastomycosis may be asymptomatic or it can present as isolated pulmonary disease, disseminated disease (pulmonary and extrapulmonary infection), or extrapulmonary disease with manifestations in the central nervous system, bone, skin, or other locations (1-11).Culture and cytopathology are the gold standard for the diagnosis of blastomycosis. However, a variety of other diagnostic tests, including antigen testing, antibody testing, and PCR, are commercially available (8,(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). Given that identification from culture may not be evident for 2 to 4 weeks and that it often requires invasive procedures to obtain specimens, there is great interest in using antigen enzyme immunoassays (EIA) for rapid, noninvasive diagnosis and monitoring of disease progression or resolution (2,4,8,19).We evaluated the use of Blastomyces urine, serum, and bronchoalveolar lavage (BAL) fluid antigen assays for the diagnosis of blastomycosis and the effects of treatment on the clearance of antigenuria at the Marshfield Clinic from 1995 to 2015. Marshfield Clinic is located in Wisconsin where blastomycosis is endemic (1,3,6,9,(23)(24)(25)(26)(27)(28). Research protocols were approved by the Marshfield Clinic Institutional Review Board. Waiver of informed consent was obtained.Patients were included if blastomycosis was confirmed by culture or cytopathology and if urine, serum, or BAL fluid antigen EIA was completed at the time of diagnosis or within 30 days of starting antifungal medication. Blastomycosis was confirmed by culture or cytopathology at Marshfield Labs using conventional techniques. Commercially available blastomycosis antigen EIA was performed at the MiraVista Diagnostics reference laboratory at the time of specimen collection using qualitative EIA prior to March 2011 or quantitative EIA thereafter. EIA results are available within 24 h of sample submission (13,14,16). All specimens were obtained as part of routine clinical evaluations. Retrospective chart review was completed for all patients.Data were abstracted into Excel 2010, and statistical analysis was completed using SAS 9.3. Categorical data were compared using the 2 test or the Fisher exact test. Continuous variables were compared using Wilcoxon rank sum, Kruskal-Wallis, or analysis of variance (ANOVA). Correlation for serial urine antigen testing was measured using Spearman's coefficient. Significance was defined as a P of Ͻ0.05.Patients with quantitative antigen EIA results were reported as negative, positive below the limit of quantification (Ͻ0.2 ng/ml), positive and quantifiable (0.2 to 14.7 ng/ml), or positiv...

Clinical Manifestations and Treatment of Blastomycosis

“…67–69 Sensitivity of antigenuria in patients with proven disease is 76.3 – 92.9% and specificity is 79.3%. 69–71 False-positives can occur in the setting of other fungal infections such as histoplasmosis, paracoccidioidomycosis and penicilliosis (talaromycosis). 67 The clinical impact of a false positive test is often minimal because paracoccidioidomycosis and penicilliosis (talaromycosis) can be removed from the differential diagnosis if the patient has not traveled to Central and South America (paracoccidioidomycosis), or Southeast Asia and China (talaromycosis).…”

“…Serial urine antigen concentrations can be used to monitor response to treatment. 71 Following initiation of therapy, a rise in antigenuria can occur (median of 11 days), which is followed by progressive decline in antigen titer with successful therapy. 71 Initial post-treatment increase in titer may be reflect increased urinary excretion of antigen due to fungal cell death.…”

“…71 Initial post-treatment increase in titer may be reflect increased urinary excretion of antigen due to fungal cell death. 71 …”

Delayed diagnosis of pediatric osseous blastomycosis of the hand: A brief report

“…Culture is the gold standard in diagnosis but can require four to six weeks for results. Serologic, sputum, and urine testing have been proven unreliable, reinforcing the importance of tissue cultures [13]. Recent advances in microsatellite genotyping have shown two distinct species, with B. gilchristii being more common in pediatric cases [5].…”

Urinary tract blastomycosis diagnosed by urine cytology

“…However, cross-reaction occurs in most patients with histoplasmosis 18 ; consequently, culture and cytopathology remain the gold standards for diagnosis of blastomycosis 19. [Color figure can be viewed at wileyonlinelibrary.com] are, however, instances in which cytology is falsely negative, or in which the overlapping morphologic features of different fungi results in misidentification of an organism.…”