Multicenter Validation of Commercial Antigenuria Reagents To Diagnose Progressive Disseminated Histoplasmosis in People Living with HIV/AIDS in Two Latin American Countries

Abstract

Histoplasmosis is an important cause of mortality in patients with AIDS, especially in countries with limited access to antiretroviral therapies and diagnostic tests. However, many disseminated infections in Latin America go undiagnosed. A simple, rapid method to detect Histoplasma capsulatum infection in regions where histoplasmosis is endemic would dramatically decrease the time to diagnosis and treatment, reducing morbidity and mortality. The aim of this study was to validate a commercial monoclonal Histoplasma galactomannan (HGM) enzyme-linked immunosorbent assay (Immuno-Mycologics [IMMY], Norman, OK, USA) in two cohorts of people living with HIV/AIDS (PLHIV). We analyzed urine samples from 589 people (466 from Guatemala and 123 from Colombia), including 546 from PLHIV and 43 from non-PLHIV controls. Sixty-three of these people (35 from Guatemala and 28 from Colombia) had confirmed histoplasmosis by isolation of H. capsulatum Using the standard curve provided by the quantitative commercial test, the sensitivity was 98% (95% confidence interval [CI], 95 to 100%) and the specificity was 97% (95% CI, 96 to 99%) (cutoff = 0.5 ng/ml). Semiquantitative results, using a calibrator of 12.5 ng/ml of Histoplasma galactomannan to calculate an enzyme immunoassay index value (EIV) for the samples, showed a sensitivity of 95% (95% CI, 89 to 100%) and a specificity of 98% (95% CI, 96 to 99%) (cutoff ≥ 2.6 EIV). This relatively simple-to-perform commercial antigenuria test showed a high performance with reproducible results in both countries, suggesting that it can be used to detect progressive disseminated histoplasmosis in PLHIV in a wide range of clinical laboratories in countries where histoplasmosis is endemic.

Keywords: AIDS; ELISA; Histoplasma capsulatum; antigen; histoplasmosis.

FIG 1

Study subjects and urine samples analyzed during the validation of the commercial IMMY Histoplasma capsulatum antigen-capture monoclonal ELISA. ¥, three patients were coinfected with Mycobacterium (M. tuberculosis, n = 2; non-M. tuberculosis, n = 1); *, of the 87 patients, 65 were identified to be infected with M. tuberculosis and 22 were identified to be infected with non-M. tuberculosis mycobacteria; ≠, of the 87 patients with Mycobacterium disease, 4 presented with coinfection with Cryptococcus (n = 2) and with Toxoplasma and Clostridium (n = 1 each).

FIG 2

Results of the H. capsulatum quantitative (A) and semiquantitative (B) antigen 2 capture ELISAs (IMMY). The levels of antigenuria in culture-proven histoplasmosis patients, persons with other diseases, and non-PLHIV controls were compared. All infectious diseases were coinfections with HIV in these patient cohorts.