Detection of airborne Coccidioides spores using lightweight portable air samplers affixed to uncrewed aircraft systems in California's Central Valley

Abstract

Coccidioidomycosis is an emerging fungal infection caused by inhalation of Coccidioides spp. spores. While airborne dispersal is critical to Coccidioides transmission, limited recovery of the pathogen from air has hindered understanding of the aerosolization and transport of spores. Here, we examine uncrewed aircraft systems (UAS) with portable, active air samplers as a novel means of capturing aerosolized Coccidioides and characterizing emissions and exposure risk. We sampled in September 2023 in eastern San Luis Obispo County, California, in an area with confirmed Coccidioides immitis in soils. We completed 41 20-minute flights across 14 sites using UAS equipped with an 8 L/min bioaerosol sampler and a low-cost particulate matter sensor. We sampled source soils and air under ambient conditions using one UAS at 1-10 m above ground level, and under a simulated high-dust event using two UAS, one at <2 m height and one at 5-12 m. We detected Coccidioides DNA in two of 41 air samples (4.9%), both under ambient conditions at 8 m above ground level, representing the highest known height of airborne Coccidioides detection. Spatially explicit UAS-based sampling could enhance understanding of Coccidioides aerobiology and enable detection in hard-to-reach or hazardous air masses, including dust storms and wildfire smoke.

Keywords: California; Coccidioides; Coccidioidomycosis; UAS; fungi; spores.

Figure 1:

Maps of sampling locations in the Carrizo Plain, CA. (A) Layout of all sites sampled, where circles denote the proportion of positive soil samples at each site and red triangles indicate the two sites with positive flights. The inset highlights the approximate location of the Carrizo Plain National Monument in California. (B) The UAS flight path for site 14 is designated in a black line. Circles denote where soil samples were concurrently collected and whether each sample was negative (light blue) or positive (dark blue) for Coccidioides. Basemap source: Esri, DigitalGlobe, GeoEye, i-cubed, USDA FSA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community.

Figure 2:

Schematics for air and soil sampling designs (A) Air sampling design for ambient and simulated high-dust flight types. (B) Systematic radial and interrupted belt transect soil sampling design. Along each transect, soil was collected from the mouths of burrows in one active precinct, and collected and pooled from the surface (top 1 cm) of soils at 10 m, 30 m, and 50 m distance from the center. Figures created using BioRender.com.