Background: Acute pulmonary histoplasmosis is a respiratory infection occurring when an otherwise healthy individual inhales a large quantity of fungal propagules. Length of exposure determines disease severity. An epidemic is influenced by factors affecting the growth and transmission of Histoplasma capsulatum var. capsulatum in nature. Objective: To identify epidemiological and clinical aspects of patients with acute pulmonary histoplasmosis in the state of Rio Grande do Sul (RS) and compare these aspects with those of other cluster outbreaks reported in Brazil. Method: The charts of 212 patients diagnosed with histoplasmosis over a 25-year period (1977-2002) were obtained from the archives of the Laboratório de Micologia from Complexo Hospitalar Santa Casa (Santa Casa Hospital Mycology Laboratory), in the city of Porto Alegre (RS). In reviewing these patient charts, we identified and included in the study cases of acute pulmonary histoplasmosis in which there was a positive culture and/or histopathological findings consistent with the diagnosis. Outbreaks were defined as one confirmed case or positive immunodifusion Histoplasma capsulatum with compatible clinical history. All reported Brazilian outbreaks were reviewed. Results: Of the 212 patient charts reviewed, 18 (8.5%) were selected for inclusion in the study. Among those 18 patients, ages ranged from 8 to 63 years (median, 35.4), and 67% were male. Epidemiological histories were suggestive of the disease in 11 patients (61%). The most common disease type, seen in 17 patients (95%), was primary acute pulmonary histoplasmosis, and there was a predominance of isolated cases. Conclusion: The identification of isolated cases and the presence of cluster outbreaks demonstrate the abundance of H. capsulatum in the soil and, together with the occurrence of all forms of the disease, confirms the assumption that Rio Grande do Sul is a hyperendemic region for histoplasmosis.

Keywords: Key words - Histoplasmosis/epidemiology. Histoplasmosis/diagnostic. Histoplasma. Medical records. Retrospective studies.