Detection of airborne C. immitis spores using unmanned aircraft systems in the Carrizo Plain, California.
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INTRODUCTION: Coccidioidomycosis is an emerging fungal infection caused by inhalation of airborne spores of the Coccidioides genus. While Coccidioides immitis has been detected in soils across California, successful recovery of C. immitis from air samples has so far been limited in California, hindering understanding of the environmental factors that give rise to dispersal of arthroconidia. Here, we examine a novel sampling strategy – air filtration with unmanned aircraft systems (UAS) – as a means of detecting C. immitis in aerosolized soil dust.
METHODS: We conducted a study in September 2023 at 14 locations across the Carrizo Plain National Monument, an area with confirmed C. immitis soil presence. We completed 41 20-minute flights using two UAS equipped with an 8 L/min aerosol sampler and Purple Air particulate matter (PM) Monitor. At each site, we sampled air under ambient conditions using a single flight at 10-20 m altitude and under a simulated high-wind event using paired flights at <5 m altitude (to mobilize dust) and 10-20 m altitude (to capture downwind spores that may be present in dust). We concurrently collected soils (n=168) using an interrupted radial transect design. We used qPCR to determine presence of C. immitis DNA on filters and soil samples. We used logistic regression models to identify associations between C. immitis detection and flight altitude, PM concentration, wind speed, temperature, and humidity.
RESULTS: Coccidioides was detected in 32% of precinct soil samples and 21% of surface soil samples. We will present this evidence of Coccidioides detection on filters, including estimated associations between Coccidioides detection, wind, and PM.
CONCLUSION: Our findings will inform a larger-scale sampling campaign being conducted over the coming year, which is aimed at understanding the aerosolization of C. immitis and potential transport in dust-generating events such as high winds and wildfires. Our study will also influence efforts to control and prevent coccidioidomycosis in endemic regions.