A 69-year-old patient with a cough had a fungal culture revealing septate hyphae with dichotomous branching. What is the likely identification?

The presence of septate hyphae with dichotomous branching in the fungal culture is highly indicative of an organism in the Aspergillus genus. Specifically, Aspergillus fumigatus is one of the most common species associated with pulmonary infections, especially in immunocompromised patients or those with chronic lung disease.

Aspergillus species, including Aspergillus fumigatus, are characterized by their septate hyphae which are typically 2-5 micrometers wide, and they form an acute angle at the branching points, often described as "dichotomous". This morphological feature is crucial for identification.

While Aspergillus niger also fits the description of forming septate hyphae, it is more associated with a black fungal mass and does not typically indicate a pulmonary infection in the same acute way as Aspergillus fumigatus. Additionally, Absidia and Mucor species are part of the Zygomycetes (now often referred to as Mucorales) that generally have coenocytic hyphae (non-septate) and broad hyphae with right-angle branching, which does not match the characteristics observed in this culture.

Thus, given that the morphology observed