Valley fever is endemic to the southwestern United States. Humans contract this fungal disease by inhaling spores of Coccidioides spp. Changes in the environment can influence the abundance and dispersal of Coccidioides spp., causing fluctuations in valley fever incidence. We combined county‐level case records from state health agencies to create a regional valley fever database for the southwestern United States, including Arizona, California, Nevada, New Mexico, and Utah. We used this data set to explore how environmental factors influenced the spatial pattern and temporal dynamics of valley fever incidence during 2000–2015. We compiled climate and environmental geospatial data sets from multiple sources to compare with valley fever incidence. These variables included air temperature, precipitation, soil moisture, surface dust concentration, normalized difference vegetation index, and cropland area. We found that valley fever incidence was greater in areas with warmer air temperatures and drier soils. The mean annual cycle of incidence varied throughout the southwestern United States and peaked following periods of low precipitation and soil moisture. From year‐to‐year, however, autumn incidence was higher following cooler, wetter, and productive springs in the San Joaquin Valley of California. In southcentral Arizona, incidence increased significantly through time. By 2015, incidence in this region was more than double the rate in the San Joaquin Valley. Our analysis provides a framework for interpreting the influence of climate change on valley fever incidence dynamics. Our results may allow the U.S. Centers for Disease Control and Prevention to improve their estimates of the spatial pattern and intensity of valley fever endemicity.

We compiled a coccidioidomycosis (Valley fever) case database for three states in the southwestern United States (US). Currently, county-level, monthly case counts are available from 2000–2015 for Arizona, California, and Nevada. We collected these data from each respective state public health agency. The Valley fever case database is available on GitHub, at https://github.com/valleyfever/valleyfevercasedata. This database may be used to examine relationships between the number of Valley fever cases and hypothesized explanatory variables such as environmental conditions, social determinants, human behavior, occupational activities, public policies, or other risk factors. We aim to provide regular updates to this database and include more states as data become available. Funding statement: M. E. Gorris received support from a Department of Defense (DoD), National Defense Science & Engineering Graduate Fellowship (32 CFR 168a). M. E. Gorris, L. A. Cat, and M. Matlock thank the UC Irvine Data Science Initiative for their funding and support. L. A. Cat acknowledges funding and support from the UC-Mexico Initiative. M. Matlock is also supported by Water UCI and the UCI Graduate Division. K. K. Treseder is supported by US NSF (EAR-1411942 and DEB-1457160) and the US Department of Energy, Office of Science, Office of Biological and Environmental Research (BER), under Award Numbers DE-PS02-09ER09-25 and DE-SC001641. J. T. Randerson received support from the Gordon and Betty Moore Foundation (GBMF#3269), NASA Soil Moisture and Interdisciplinary Science Program, and the U.S. Dept. of Energy Office of Science RUBISCO Science Focus Area. C. S. Zender acknowledges support from the Borrego Valley Endowment Fund and DOE ACME DE-SC0012998.