Composting can be a potential health risk for people prone to lung infections caused by Asperigillus fumigatus (pulmonary aspergillosis), as well as immunocompetent individuals with increased exposure to A fumigatus fungal spores. These findings were published in Applied and environmental microbiology.
A fumigatus is a fungus that plays an important environmental role as a decomposer. Its small size (2-3 mcL) makes it easily aerosolizable and transportable on air currents, and its fungal action spores have been associated with an increased risk of severe asthma with fungal sensitization, allergic bronchopulmonary aspergillosis, and chronic pulmonary aspergillosis.
A citizen science project was conducted in the UK in 2019 to determine whether gardening activities are associated with an increased risk of exposure to A fumigatus spores resistant to triazole antifungals. A total of 246 people collected 509 soil samples from their gardens, of which 5174 A fumigatus isolates were cultured and evaluated for tebuconazole resistance. The researchers noted that tebuconazole is “the third most sprayed triazole fungicide in the UK, conferring cross-resistance to medical triazoles used to treat A fumigatus lung infections in humans.
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Of the 509 soil samples grown, 64% yielded a total of 5,174 A fumigatus isolates and 20% developed a total of 736 isolates resistant to tebuconazole A fumigatus isolated. The researchers noted that most soil samples (89%) were taken from a single location in a residential garden.
The average concentration of spores and mycelial fragments in all soil samples from which crops were grown A fumigatus was 316 colony forming units (CFU)/g. Samples taken from a manure bag showed an increased concentration of spores (600 CFU/g). The average concentration of spores and mycelial fragments in all soil samples from which crops grew resistant to tebuconazole A fumigatus was 146 CFU/g, with concentrations increasing the most in soil samples taken from compost heaps (214 CFU/g).
The researchers found that the only significant predictor of growth A fumigatus was the place where the soil samples were taken (c267.3; P <.01 the chances of growing>A fumigatus were significantly increased among soil samples collected in compost bags (odds ratio [OR], 15.70; 95% CI, 5.50-66.19; P P P <.01 similar results were observed for the probability of becoming resistant to tebuconazole with a significantly increased among samples collected from compost bags ci>P P <.01>
According to the researchers, “The evidence presented here supports the recommendation of [the use of facemasks] during compost handling and the introduction of health warnings on compost bags [in regard] for [the risk for] inhale A fumigatus [spores].” They noted that “measures could also be taken by compost producers to sterilize the compost before packaging, thus killing the A fumigatus spores and eliminating the immediate danger it poses to [individual].”
Reference
Shelton JMG, Collins R, Uzzell CB, et al. Citizen science monitoring of triazole resistant Aspergillus fumigatus in residential garden soils in the UK. Environ Microbiol App. Published online January 5, 2022. doi:10.1128/AEM.02061-21
