Histoplasmosis: Detection of Histoplasma Capsulatum in Fungal Cultures Over a Decade in the State Reference Laboratory

Histoplasma capsulatum is a thermally dimorphic fungus with global distribution, prevalent in Latin America and Africa, especially in environments contaminated with bird and bat droppings. Infection occurs through inhalation of conidia and may result in histoplasmosis, which can be severe in people living with HIV/AIDS (PLWHA) with low CD4 counts (<150 cells/µL). In the Americas, approximately 15,000 new cases and 9,000 deaths are estimated annually. Treatment includes amphotericin B (conventional and liposomal) and itraconazole. Diagnosis involves methods such as histopathology, fungal culture, antigen/antibody tests, and molecular techniques. Given the relevance of the topic, this study was conducted. In this context, the objective was to survey fungal cultures processed between 2015 and 2024, with emphasis on those positive for H. capsulatum. In this quantitative study, data from fungal isolates from the Mycology Section of the state reference laboratory were analyzed. Samples were obtained from patients seen at a reference hospital for tropical diseases and PLWHA from municipalities within the state and elsewhere. A total of 31,827 records of fungal cultures performed between January 2015 and December 2024 were included, extracted from the Laboratory Environment Management System (GAL). Repeated, inconclusive, or indeterminate samples were excluded. The number of samples with cultures positive for H. capsulatum, fungal growth time, and types of biological specimens were evaluated. The study was approved by a Research Ethics Committee (CAAE: 55315822.2.0000.5082). Of the 31,827 samples analyzed, 23.14% (n = 5,982) showed fungal growth, of which 12.95% (n = 775) were positive for H. capsulatum, representing 393 distinct cases (3.03% of the total). The specimens with the highest positivity rates were blood (71.61%), bone marrow (8.90%), and tissue fragments (3.74%). Growth time ranged from 4 to 38 days (mean 16.21 days), with incubation on Sabouraud and Mycosel agar at 28 ± 2°C. The volume of samples processed during the period was substantial. Although the proportion of positivity for H. capsulatum was relatively small, it is clinically relevant. Blood was the predominant specimen type, and the maximum growth time exceeded one month. These findings reinforce the importance of recognizing the limitations of culture, as its sensitivity and specificity vary depending on the site of infection and fungal burden, even though it remains the gold standard.