Histoplasmosis in a State Where It Is Not Known to Be Endemic — Montana, 2012–2013

Histoplasmosis is caused by infection with the dimorphic fungus, Histoplasma capsulatum, following inhalation of contaminated soil. Among symptomatic patients, the most common clinical presentation is acute pneumonia. Persons with compromised immune systems are at risk for disseminated histoplasmosis, a severe illness requiring antifungal therapy that is often characterized by fever, malaise, anorexia, and weight loss. H. capsulatum is endemic in the Ohio River and Mississippi River valleys, where it is found in soil enriched with bird droppings and bat guano. During November 2012-February 2013, histoplasmosis was diagnosed in four Montana residents by four different physicians. No epidemiologic links among the cases were identified. Each patient's medical records were reviewed, and their exposure and travel histories were obtained. Three patients reported no recent travel outside of Montana and likely were exposed in Montana, which is west of areas where H. capsulatum is recognized as endemic. One patient reported recent travel to California, where she was exposed to potting soil containing bat guano. Low clinical suspicion, probably related to lack of history of exposure to areas where H. capsulatum is known to be endemic, likely delayed diagnosis and appropriate therapy for three patients. Health-care providers should be aware of the possibility of histoplasmosis in Montana and consider the diagnosis in patients with clinically compatible illnesses.