A patient diagnosed with a fungal infection shows reticulonodular infiltrates on a chest x-ray. What is the infectious agent?

The infectious agent responsible for a fungal infection that presents with reticulonodular infiltrates on a chest X-ray is Histoplasma capsulatum. This organism is well-known for causing pulmonary histoplasmosis, particularly in regions where the fungus is endemic, such as the Ohio and Mississippi River valleys.

Histoplasma capsulatum typically thrives in environments where bird or bat droppings provide nutrients, and transmission usually occurs through inhalation of aerosolized spores. The reticulonodular pattern observed on imaging studies reflects the presence of granulomatous inflammation and pulmonary nodules, which is characteristic of histoplasmosis.

In contrast, other fungi mentioned have distinct presentations or associated imaging findings. For example, Candida albicans primarily causes mucosal infections or disseminated candidiasis, rather than a pulmonary infiltrate pattern. Aspergillus species are often associated with cavitary lesions on imaging and typically present with a different clinical picture, such as aspergilloma or invasive pulmonary aspergillosis. Meanwhile, Cryptococcus neoformans often leads to cryptococcal pneumonia in immunocompromised individuals, but it is more frequently associated with meningoencephalitis and does not typically present with the reticulonodular pattern seen in histoplas