GC23E-06 – The Influence of Current and Future Climate on the Spatial Distribution of Coccidioidomycosis in the Southwestern United States


Morgan E. Gorris
University of California Irvine
Forrest M. Hoffman (forrest at climatemodeling dot org)
Oak Ridge National Laboratory
Charles S. Zender
University of California Irvine
Kathleen K. Treseder
University of California Irvine
James T. Randerson
University of California Irvine


Climate Change Impacts on Human Health and the Environment I
Tuesday, December 12, 2017 14:55–15:10
New Orleans Ernest N. Morial Convention Center – 267–268


Coccidioidomycosis, otherwise known as valley fever, is an infectious fungal disease currently endemic to the southwestern U.S. The magnitude, spatial distribution, and seasonality of valley fever incidence is shaped by variations in regional climate. As such, climate change may cause new communities to become at risk for contracting this disease. Humans contract valley fever by inhaling fungal spores of the genus Coccidioides. Coccidioides grow in the soil as a mycelium, and when stressed, autolyze into spores 2--5 µm in length. Spores can become airborne from any natural or anthropogenic soil disturbance, which can be exacerbated by dry soil conditions. Understanding the relationship between climate and valley fever incidence is critical for future disease risk management. We explored several multivariate techniques to create a predictive model of county-level valley fever incidence throughout the southwestern U.S., including Arizona, California, New Mexico, Nevada, and Utah. We incorporated surface air temperature, precipitation, soil moisture, surface dust concentrations, leaf area index, and the amount of agricultural land, all of which influence valley fever incidence. A log-linear regression model that incorporated surface air temperature, soil moisture, surface dust concentration, and the amount of agricultural land explained 34% of the county-level variance in annual average valley fever incidence. We used this model to predict valley fever incidence for the Representative Concentration Pathway 8.5 using simulation output from the Community Earth System Model. In our analysis, we describe how regional hotspots of valley fever incidence may shift with sustained warming and drying in the southwestern U.S. Our predictive model of valley fever incidence may help mitigate future health impacts of valley fever by informing health officials and policy makers of the climate conditions suitable for disease outbreak.

Plain Language Summary

Valley fever, formally known as coccidioidomycosis, is a fungal disease most common in the southwestern U.S. People become sick with valley fever when they inhale fungal spores that originate in the desert soil, then loft into the air from natural (e.g., high winds) or human-caused (e.g., construction) soil disturbance. Both the amount of fungal spores and when these spores enter the air are influenced by local climate conditions. As our climate changes and the fungi shift to live in more suitable conditions, new communities will become at risk for contracting this disease. Understanding the relationship between climate and the amount of valley fever cases is critical for doctors and policy makers to prepare for this disease. We created a model for the southwestern U.S. that predicts what communities may become susceptible to contracting valley fever. Our model included Arizona, California, Nevada, New Mexico, and Utah. We then used estimates of future climate conditions to examine how the amount of valley fever cases may change. This model may help reduce the cost and health effects of valley fever by informing communities when the climate conditions are right for disease outbreak.

Forrest M. Hoffman (forrest at climatemodeling dot org)