Azole-resistantAspergillus fumigatus
What you need to know
Aspergillus fumigatus (A. fumigatus) causes invasive mold infections in people. It can cause life-threatening infections, especially in people with weakened immune systems. Most infections occur after people inhale airborne spores (tiny particles released by fungi into the air). A. fumigatus infections are typically treated with azole antifungal drugs. Azoles can also be used as fungicides, which are chemicals used to prevent and control fungal diseases in plants. They are widely used in agriculture, on ornamental plants, and in other settings where plants are grown. The use of azole antifungal drugs in people and azole fungicides in the environment can contribute to the development of azole-resistant A. fumigatus.
What we know about resistance
Azole-resistant A. fumigatus infections have been identified in the United States, but the burden is not well understood. Over the past decade, studies in some parts of the world have found that up to 20% of A. fumigatus infections are resistant to azole antifungals. However, limited surveillance data from 2022 to 2025 suggest that azole resistance in A. fumigatus remains uncommon in the United States, as it was identified in less than 5% of clinical isolates (pure samples of A. fumigatus).
Azole resistance can limit treatment options and is associated with increased treatment failures and worse health outcomes. Detecting resistant infections is challenging because A. fumigatus infections can present with symptoms similar to other respiratory infections, and most U.S. laboratories do not routinely test for drug resistance. As a result, resistant infections may go unrecognized, leading to delays in appropriate treatment.
What CDC is doing
Although surveillance for A. fumigatus infections in the United States is currently limited, CDC is working with state and local partners through the Antimicrobial Resistance Laboratory Network to improve detection, better understand disease burden, and identify prevention strategies. CDC also conducts additional A. fumigatus surveillance through the Emerging Infections Program in Georgia.