Environmental Hotspots for Azole Resistance Selection of Aspergillus fumigatus, the Netherlands

Azole resistance is a major concern for treatment of infections with Aspergillus fumigatus. Environmental resistance selection is a main route for Aspergillus spp. to acquire azole resistance. We investigated the presence of environmental hotspots for resistance selection in the Netherlands on the basis of the ability of A. fumigatus to grow and reproduce in the presence of azole fungicide residues. We identified 3 hotspots: flower bulb waste, green waste material, and wood chippings. We recovered azole-resistant A. fumigatus from these sites; all fungi contained cyp51A tandem repeat–mediated resistance mechanisms identical to those found in clinical isolates. Tebuconazole, epoxiconazole, and prothioconazole were the most frequently found fungicide residues. Stockpiles of plant waste contained the highest levels of azole-resistant A. fumigatus, and active aerobic composting reduced Aspergillus colony counts. Preventing plant waste stockpiling or creating unfavorable conditions for A. fumigatus to grow in stockpiles might reduce environmental resistance burden.