Cameron Kiongo is a Sacramento Valley College Corp Fellow with Cool Davis and a fourth-year undergraduate student majoring in Biochecmistry and Molecular Biology. Cameron is from the Moreno Valley, California, where she developed a love for the color purple and a belief in a holistic approach to community care. Cameron plans on continuing her education and becoming a physician associate after graduating from UC Davis. She is pictured in this article.

Valley Fever is a disease caused by fungi spores released into the air. Coccidioides, the fungus that causes Valley fever, is found in soil and can infect people when released into the air as a result of soil disruption. Symptoms of Valley Fever include fever, fatigue, cough, shortness of breath, rashes, muscle ache of joint pain, and night sweats. Although most symptoms of Valley Fever go away within a couple of weeks, more severe cases of Valley Fever can be lethal. Rare cases of the disease can spread to and infect other parts of the body such as the brain, causing meningitis.

In the US, Valley Fever cases are most prevalent in the Southwest, including states such as California, Arizona, Nevada, and New Mexico. Coccidioides primarily exists in the Southwest region of the US because of the favorable climate. Warm conditions are favorable for the Valley Fever fungus to replicate in soil. Patterns of record breaking temperatures in the western portion of the US allows coccidioides to survive outside its usual region. According to the CDC, new cases of Valley Fever have been reported in parts of the Pacific Northwest. The CDC reports that the changes in climate may lead to more Valley Fever infections because “fungi become more adapted to surviving in humans” as the gap between human and regional temperatures lessens (CDC, 2020).

California cases increase with temperatures

Valley Fever cases and areas of infection are on the rise in California, and changes to our state’s climate have made it easier for the fungus to be transmitted. Climbing temperatures during summer months allows coccidioides to survive in areas that were previously too cold. Longer periods of unusual warm weather also extend the Valley Fever season. Increased rainfall in the winter months also leads to higher levels of coccidioides in the soil, heightening the potential of spore transmission during periods of drought. As a result, these climate related impacts increase the transmission risk for Valley Fever and are creating unsafe working environments for California’s agricultural workers.

California’s recent record breaking heat as a result of climate change also impacts the transmission of Valley Fever. The Valley Fever season usually begins in the late summer months and lasts until fall. The California Office of Environmental Health and Hazard Assessment (OEHHA) predicts that the Valley Fever season will be extended later into the fall as temperatures continue to rise above average for that time of year.

To learn more about Valley Fever transmission in California , I had the pleasure of speaking with Dr. Aimee Sisson, Public Health Officer of the Yolo County Health and Human Services Agency. When asked about the trend in Valley Fever cases, Dr. Sisson said, “cases in Yolo County increased between 2001 and 2022 with a peak in 2019.”

Cycles of drought and flood also key contributors

The California Office of Environmental Health and Hazard Assessment (OEHHA) also lists rainfall and drought as another key contributor to the transmission of Valley Fever. The fungus coccidioides becomes activated when enough rainfall is able to penetrate deep into the soil. Its spores are then released into the air when soil is disturbed, and dust gets released. Extreme rainfall as a result of climate change and periods of drought in the state creates favorable conditions for the Valley Fever fungus to spread. Heavier rainfall implies that more coccidioides spores may be created in soil. During periods of drought, the hot and dry environment allows for the spores to easily spread with the aid of dirt and debris. Transmission of the spores is exacerbated with strong winds and dust storms.

Risks to agricultural workers

California’s agricultural workers are among those at higher risk for catching Valley Fever  because their line of work involves soil disruption. California’s largest agricultural county, Kern County has the highest number or reported cases of Valley Fever in the state. Other big agricultural counties in California like Fresno, Merced, and King country also have high cases of Valley Fever. The climate related impacts on Valley Fever put agricultural workers at risk for infection because they are in constant contact with dust, soil, and other debris. Exposure to the Valley Fever fungus also depends on the type of crop cultivated. Root and bulb vegetables are more likely to harbor Valley Fever as opposed to crops managed without disruption to the soil. A study from UC Davis health noted that “leaf removal (primarily used in grape cultivation) had a 60% reduction in their odds of getting the disease” (UC Davis Health, 2020).

However, Dr, Sission advises that “we need to look at not just agriculture activity when assessing Valley fever risks.” Other industries such as construction also put individuals at higher risk for Valley fever through soil disruption. “For the general public, CDPH recommends staying inside with doors and windows shut on windy and dusty days, covering bare soil with plants or ground cover, avoiding outdoor activities that involve close contact with dirt or dust, and avoiding dusty areas in general. For people who need to be outside in dusty areas, CDPH recommends wearing a well-fitted N95 respirator to protect against Valley fever.”


Luckily, Yolo County residents are not in a high risk area for contracting Valley Fever. The California Department of Public Health published a Valley Fever Dashboard that monitors the incidence rate of Valley Fever through various criteria. Out of the thousands of reported Valley Fever cases in California, Yolo County has consistently seen less than 5 annual cases of Valley Fever since 2019.

In conclusion, Valley Fever is a disease that is caused by Coccidioides fungal spores that are dispersed in the air as a result of soil disruption. California amongst other states in the southwest region have and will likely continue to experience a dramatic increase in Valley Fever cases due to the ongoing climate crisis. Certain industries that come in contact with disrupted soil, such as the agricultural industry, make up the majority of people at high risk for contracting Valley Fever.

A special thanks to Dr. Sisson, Yolo County Public Health Officer, for her generous gift of time and expertise!


Valley Fever (coccidioidomycosis) | Centers For Disease Control and Prevention

Climate Change and Infectious Diseases | Centers For Disease Control and Prevention

Indicators of Climate Change in California | California Office of Environmental Health Hazard Assessment

Risk factors for Valley fever among Hispanic California farmworkers | UC Davis Health

Valley Fever in California Dashboard | California Department of Public Health