American Board of Internal Medicine (ABIM) Certification Practice Exam

In which geographic areas is Histoplasmosis primarily endemic in the United States?

1. Pacific Northwest

2. Great Plains

3. Ohio and Mississippi river valleys

4. Appalachian mountains

The correct answer is: Ohio and Mississippi river valleys

Histoplasmosis is a fungal infection caused by Histoplasma capsulatum, and it is primarily endemic in specific regions where environmental conditions favor the growth of the fungus. In the United States, the areas most famously associated with this infection are the Ohio and Mississippi River valleys. These regions have the necessary warm, moist environments and specific soil characteristics that contribute to the proliferation of the fungus, which often thrives in areas with bat or bird droppings. In contrast, the other geographic areas mentioned do not exhibit the same level of endemicity for histoplasmosis. While the Pacific Northwest does have its own unique pathogens and infections, it is not a known hotspot for histoplasmosis. The Great Plains, although they may have occurrences of the disease, are not recognized as a primary endemic zone as the Ohio and Mississippi River valleys are. Similarly, the Appalachian mountains do have some presence of the fungus, but they are not as prominently associated with histoplasmosis compared to the designated river valleys. This understanding of geographic distribution is critical for diagnosis, treatment, and prevention strategies for healthcare providers, particularly those working in endemic regions. Being aware of the areas where histoplasmosis is most prevalent can help clinicians be more vigilant when evaluating patients who present with respiratory symptoms or