Modeling Valley Fever Incidence in Arizona Using a Satellite-Derived Soil Moisture Proxy

Abstract

Valley Fever is caused by inhalation of spores from the soil-dwelling fungus Coccidioides spp. Pima, Pinal, and Maricopa counties, Arizona, have the highest Valley Fever incidence on earth. Despite reported links between climate, habitat, disease timing, and seasonality, relationships between the fungus and its putative affinity to moist soils are poorly understood. We used Normalized Difference Vegetation Index (NDVI) time series from the Advanced Very High Resolution Radiometer (AVHRR) sensor to compare soil moisture variations with disease incidence. Results suggest moist soils in the early spring, resulting from antecedent winter precipitation, correlate with increased incidence in these counties up to a year later.