Fatal Fungicide-Associated Triazole-Resistant Aspergillus fumigatus Infection, Pennsylvania, USA

We report a fatal infection in a 65-year-old immunocompromised male patient caused by pan-triazole–resistant Aspergillus fumigatus containing a TR34/L98H genetic mutation linked to agricultural fungicide use. Clinical and environmental surveillance of triazole-resistant A. fumigatus is needed in the United States to prevent spread and guide healthcare and agricultural practices.

[Kennedy Bradley] Triazoles are a class of antifungal agents that are widely used for the prophylaxis and treatment of invasive fungal infection. For example, voriconazole, which is a second-generation triazole, it's a first-line treatment for patients with invasive aspergillosis. Other medical triazoles include fluconazole, itraconazole, and posaconazole. And what's interesting about triazoles is that they are widely used in both clinical and agricultural settings and are highly effective against fungal pathogens of both humans and plants, leading to their widespread use in both settings.

[Sarah Gregory] What is Aspergillus fumigatus?
[Kennedy Bradley] Aspergillus fumigatus is the most common species of Aspergillus, which is a genus of fungi, that are comprised of approximately 180 species of mold. Like other Aspergillus species, Aspergillus fumigatus is commonly found throughout the environment, particularly in soil, compost, and other decaying plant materials. But it can also be found in household dust, building materials, and in the ambient air. So it goes without saying, you will likely be able to find Aspergillus in our home. And unlike other fungi, Aspergillus fumigatus is thermal tolerant, meaning that it can grow and thrive in normal and high body temperatures, including during fever response. And it's also the most common species of invasive aspergillosis, which is a life-threatening fungal infection. And while invasive aspergillosis most commonly affects the lungs, it can also spread to other parts of the body.
[Sarah Gregory] Who does it primarily affect?
[Kennedy Bradley] Invasive aspergillosis involving Aspergillus fumigatus primarily affects immunocompromised patients. So for example, patients with hematologic malignancies and cell or organ transplant patients, or patients receiving immunosuppressive medication. And it can also affect patients who are critically ill, and we're starting to see some of these cases of invasive Aspergillus among patients with severe influenza or COVID-19 infection.
[Sarah Gregory] Finally, a fungicide is?
[Kennedy Bradley] So fungicides are a specific type of pesticide, and they're used to kill or inhibit the growth of fungi and their source. And in agriculture, fungicides have been widely used for centuries to treat plant infection, prevent crop loss, and increase agricultural yield. So for example, in places such as the Midwest and the Southeast, triazole fungicides are widely used on crops, such as wheat, corn, or soybeans. And in addition to their use in agriculture, fungicides may also be used in nonfood specific settings to control mold and mildew in our homes and commercial property. And they are also used to preserve wood and other materials in the environment.
[Sarah Gregory] What does an agricultural fungicide then have to do with resistance to an antifungal medication in a person?
[Kennedy Bradley] That's a great question, Sarah. Recent research in whole-genome sequencing is finding that these resistant Aspergillus fumigatus strains found in the environment are closely related to clinical isolates. For example, resistant strains carrying the TR34/L98 mutation (which is essentially just a gene mutation linked to environmental fungicide use) that can cause pantriazole resistance in patients has also been found in peanut crop debris that had been treated with agricultural triazole fungicides that are similarly structured to medical triazoles. And research is also finding that these isolates are both resistant to fungicides used on plants in the environment and azole medications used in clinical settings. And so, due to the widespread use of triazole fungicides in agriculture, researchers suspect that resistance is developing in the environment due to selection pressure.
[Sarah Gregory] Do we know why fungicides are used so dramatically, as antibiotic use is supposedly waning?
[Kennedy Bradley] So several factors may explain the increase in fungicide use, including increased crop production to meet demands, increases in plant diseases in certain regions, and marketing of fungicides on field crops to farmers such as…for reasons such as plant safety. Fungicides are still commonly used and added to spray paint during insurance applications, which are essentially prophylactic treatments of crops.
[ So again, we know that these infections existed, and we know that resistance is a concern globally. So we wrote this as an opportunity to further fuel conversations regarding fungal infections and hopefully to define the scope of this issue in the United States.
[Sarah Gregory] Tell us about the patient and what happened to him.
[Kennedy Bradley] Sure. So the patient was a 65-year-old male who had a complex medical history. So the patient had previously underwent chimeric antigen receptor T-cell therapy for acute myeloid leukemia, and one month prior to hospital admission, the patient had received a stem cell transplant which was further complicated by cutaneous graft-versus-host disease. And despite topical therapies, the patient was admitted to the hospital due to worsening rashes, fever, and lethargy. And shortly after admission, the patient was transferred to the intensive care unit for wound management and treatment for hypovolemic shock. Following the patient's positive Aspergillus fumigatus bronchial culture, clinicians initiated voriconazole therapy for probable invasive aspergillosis. Unfortunately, however, the patient's condition continued to worsen, and the patient's family had decided to focus on comfort care. The patient expired on hospital day 28, and the autopsy determined that that cause of death was sepsis from disseminated Aspergillus fumigatus and Rhizopus species infection.
[Sarah Gregory] How and where was the susceptibility testing done? Can any lab do it?
[Kennedy Bradley] Unfortunately, most US clinical laboratories do not perform antifungal susceptibility testing. However, as I mentioned earlier, susceptibility testing is available through the CDC's Antibiotic Resistance Laboratory Network. Therefore in this case, the hospital laboratory sent the patient's isolate to the CDC as a part of ongoing passive surveillance which was collaboratively established by the Philadelphia Department of Public Health, the CDC, and the hospital laboratory. So the CDC performed broth microdilution to determine the MICs of itraconazole and voriconazole for the isolate. And for reference, the minimum inhibitory concentration assay (or MIC) is widely used to measure the susceptibility of fungal strains to antifungal agents. And following susceptibility testing, the CDC performed a DNA sequence analysis of the CYP51A gene and determined that the isolate contained the TR34 gene mutation, which has been linked to environmental fungicide use.
[Sarah Gregory] Okay. A person has got this resistant version so they can't get the triazole. Are there alternative treatments?
[Kennedy Bradley] That's a great question. Guidelines for treating these resistant infections are lacking. However, an international panel of experts has published practical recommendations for clinicians pending better quality evidence. Antifungal therapy for patients with these resistant Aspergillus infections is complex, and it really depends on the type of mutation involved and the patient's individual situation. But treatment might involve combination therapy such as voriconazole plus echinocandin or liposomal amphotericin B.
[Sarah Gregory] What do you think is the public heath importance of your report?
[Kennedy Bradley] So this report really underscores the potential severity of triazoleresistant Aspergillus fumigatus infections. With mutations linked to the environment, we use a triazole in immunocompromised patients. As I previously mentioned, invasive aspergillosis is not a reportable condition in the United States, so the scope of azole-resistance is not welldefined. So this report helped to define the scope of azole-resistance in the United States, and this report I hope will highlight the importance of considering the possibility of drugresistant Aspergillus fumigatus infection in clinical settings among patients with invasive aspergillosis who do not improve with first-line therapy.
[ we think about ringworm, vaginal yeast infections, or maybe even athlete's foot. But the issue with fungal infections that are resistant to currently available antifungal medications are not commonly addressed. Therefore, raising awareness of these infections will help to improve understanding. I think it's also really important to consider the concept of One Health when thinking about resistance. As you know, antifungal resistance is not just a concern to human health, but also to plant health and animal health. We also need more robust laboratory-based surveillance and diagnostic tools for Aspergillus infections, including systematic antifungal susceptibility testing. Performing susceptibility testing and detecting resistant strains early can not only help to define the scope of this issue in the US, but also to help to prevent the spread and inform future interventions, if possible. And lastly, we need surveillance-active surveillance. Again, Aspergillus infections are severely underdiagnosed. So conducting active surveillance can help us to better understand the true burden of these resistant infections.
[ [Kennedy Bradley] It goes without saying that it's really important that clinicians are being good stewards in order to preserve the effectiveness of these lifesaving medications and also for any future drugs that may become available. Health systems should also ensure that they're monitoring antifungal usage and appropriateness of prescribing, similarly to what's being done for antibiotics.
[Sarah Gregory] Is there a way for people to protect themselves?
[Kennedy Bradley] So it is difficult to avoid breathing in the spores because the fungus is so common in the environment. However, there may be a few ways to lower the chances of developing a severe Aspergillus infection for high-risk patients. So for example, avoiding areas with a lot of dust like construction sites or evacuation sites, which are some of the areas where the fungus tends to thrive, or wear an N95 respirator while visiting these sorts of sites where Aspergillus may be more prevalent. High-risk patients should also avoid activities that involve close contact to soil or dust, such as yardwork and gardening, if possible. Or wear protective clothing and gloves while performing activities in handling things such as soil, mulch, and manure-again, all places where Aspergillus may be more prevalent.
[Sarah Gregory] Kennedy, tell us about your job.
[Kennedy Bradley] Sure. I'm a CSTE Applied Epidemiology Fellow at the Philadelphia Department of Public Health within the Healthcare-associated Infections and Antimicrobial Resistance Program. My primary subject area is in healthcare-associated infections. However, we also focus on other communicable diseases such as COVID-19. And as a fellow, I've worked on a variety of projects that are designed to address certain public health competencies such as epidemiologic methods. I also collaborate often with other programs within the Division of Disease Control (such as the TB control program, the bioterrorism program) for efforts such as