Hotspots of Bacterial Pathogen Abundance and Exposure Risk in Soils of the Contiguous United States

Soils are reservoirs of pathogenic bacteria that cause human illness, particularly after mobilizing events such as extreme rain. Land-use patterns (e.g., proximity to agriculture) and soil properties (e.g., moisture) are associated with abundance of individual pathogenic bacteria. However, there are major uncertainties in (a) the importance of local/regional land-use decisions relative to overall natural variability of pathogenicity and (b) the correlations among pathogen abundance, climate-linked physical processes increasing pathogen mobility, and the vulnerability of human receptors. This impairs identification of priority areas for outbreak surveillance, which has traditionally focused on food and water distribution networks, and the development of process-based risk screening models. Here, we analyze a novel data set of 622 soil samples covering 42 of the 48 contiguous United States. We describe (a) the relationship between putative pathogenicity and natural and land-use drivers and (b) how hotspots of putative pathogen abundance intersect with climate-linked hazard of mobilization via fire, floods, wind, and fluvial transport, and the social vulnerability of local human populations. Variability in putative pathogenicity can be partially explained by known drivers, with natural variables having greater explanatory power than land-use variables. Relative abundance of putative pathogens is generally higher in forested ecoregions, notably in the eastern and southeastern United States and in proximity to surface waters. Higher relative abundance of putative pathogens, climate risks promoting pathogen mobility, and a relatively vulnerable rural population intersect in the southeastern United States. Integrated sampling and modeling are needed to monitor and forecast health risks from soilborne pathogens.