Antimicrobial-Resistant Aspergillus

At a glance

  • Antimicrobial resistance occurs when bacteria and fungi are able to survive antimicrobial drugs.
  • Emerging azole-resistant Aspergillus fumigatus (A. fumigatus) is a growing global public health concern.
  • Azoles are the first line medication for people infected with A. fumigatus.
Calendar and antifungal medicine


Antimicrobial resistance is emerging in one type of Aspergillus species called Aspergillus fumigatus (A. fumigatus). This is a common mold in the environment and the leading cause of invasive mold infections in people. Antimicrobial resistance occurs when bacteria and fungi are able to survive the antimicrobial drugs that treat infections. As a result, the germs continue to grow.

Azole-resistant A. fumigatus is on the CDC 2019 Antibiotic Resistance Threats Report Watch List because it has the potential to rapidly spread.

Azole-resistant aspergillosis

A. fumigatus can result in infection, called aspergillosis, in people who have weakened immune systems, underlying diseases, or had transplants. Patients with severe cases of respiratory infections, like the flu or COVID-19, have also developed aspergillosis.

Triazole antifungal drugs, commonly called azoles, are the primary treatment for aspergillosis. Azole-resistant A. fumigatus infections are difficult to treat, and these patients are up to 33% more likely to die than patients with infections that can be treated with azoles.

Emergence globally and within the United States

The true burden of azole-resistant aspergillosis in the United States is unknown. A few factors make it difficult to estimate:

  • Aspergillosis is one of the leading missed diagnoses in intensive care units.
  • Until recently, clinicians have had limited access to antifungal susceptibility testing.

An estimated 19% of A. fumigatus infections are resistant to azole antifungals in medical centers in some parts of the world. In a large U.S. study, antimicrobial resistance was identified in up to 7% of Aspergillus specimens from patients with stem cell and organ transplants.

Azole resistance develops in the body and in the environment

We know of two ways that A. fumigatus can develop resistance to azoles.

  1. Inside the body: Strains of A. fumigatus in people who take azole antifungals for a long period of time can become resistant, survive treatment, and continue to cause infection.
  2. Outside the body: Strains of A. fumigatus on decaying plants in the environment can be exposed to azole compounds used as fungicides that are chemically similar to azole antifungal medications. These strains can develop resistance to azoles.

Some patients with chronic A. fumigatus infections take azole antifungals over a long time.

Azole fungicide use

Azole fungicides are used throughout the world to treat plant infections, prevent crop loss, and increase production. Patients with azole-resistant aspergillosis have been infected with A. fumigatus strains similar to those associated with agricultural azole fungicide use. Resistant Aspergillus infections are also found in people who have not taken azole antifungals.

A direct association between the quantity of U.S. agricultural azole fungicide use and human infections has not been established. The US Geological Survey estimated that the use of agricultural azole fungicide quadrupled from 2013 to 2016.

Preventing the environmental spread of azole-resistant A. fumigatus in the US.

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