Impacts of land use and fallowing on coccidioidomycosis incidence in California: A population-based longitudinal study.

Coccidioidomycosis (Valley fever) is a growing public health concern in the western U.S., with California reporting more than an eightfold rise in cases over the past two decades. As climate change, groundwater regulation, and prolonged drought drive major agricultural land-use shifts in the state, including widespread retirement of cultivated lands (i.e., fallowing), understanding their effects on this soil-borne fungal infection is critical. We linked 65,657 confirmed, geolocated cases (2008-2021) to high-resolution maps distinguishing natural vegetation, crop types, and fallowed fields to quantify how land use and land cover were associated with disease rates. Flexible statistical models showed that natural land covers, shrubland, barren ground, and grassland, were associated with higher incidence. Some agricultural uses (grain/hay, field crops, corn, and cotton) were associated with higher incidence, whereas others (orchards, rice, and truck crops/berries) were associated with lower incidence. Recently fallowed land (1 to 4 years) was linked to higher incidence, but the effect depended on prior cultivation. These findings indicate that land use changes may inadvertently impact coccidioidomycosis risk, underscoring the need for dust control and other measures to protect communities.