Communities ringed by dry shrubland, bare ground and recently idled farm fields report higher rates of Valley fever than otherwise similar California communities, according to a large new analysis published in Science Advances. The finding arrives as the state moves into the months when Valley fever diagnoses typically peak.
The timing is not incidental. California health officials note that more people breathe in the fungus during the dry stretch of summer and early fall, and because symptoms surface one to three weeks later, reported cases cluster in fall and early winter. Households across the San Joaquin Valley, the Central Coast and inland Southern California are entering that window now.
The study does not describe a new disease or a new outbreak. It describes where the risk lies on the map and points to land that is changing hands, drying out, or going out of production as groundwater rules and drought reshape California agriculture. That is a concrete exposure question for farmworkers, construction crews and the families who live downwind of them.
Dry Land, Dust, and the Path Spores Take into Nearby Communities
Researchers from UC San Diego and UC Berkeley examined 65,657 confirmed Valley fever cases reported to the state between April 2008 and March 2021, across 20 California counties where the disease is most common. Those counties averaged at least five cases per 100,000 residents a year and at least 10 cases annually. The team then compared where patients lived with high-resolution crop and land-cover data, adjusting for climate, elevation, socioeconomic conditions, and employment in agriculture and construction.
The strongest signals came from open, dry ground. A one-standard-deviation increase in surrounding shrubland was associated with a 62 percent higher Valley fever incidence. Barren land was associated with a 34 percent higher incidence, and grassland with an 18 percent higher incidence, according to CIDRAP. The researchers suggest these landscapes may both favor fungal growth in soil and generate the dust that carries spores toward populated areas.
Farmland cut both ways, which is the part most coverage will flatten. Greater areas of grain and hay fields, field crops such as sorghum, soybeans, corn, and cotton, and fields with multiple harvests were tracked at higher incidence. But orchards, fruits, vegetables, flowers, berries, and rice were associated with a lower incidence.
Fallowing produced a similarly split result. The total amount of fallow land near a community was not significantly associated with Valley fever. Larger areas of newly fallowed land were. That association also varied with what had grown there previously, with mixed cropping histories associated with a higher incidence.
Valley fever is not contagious. It is caused by inhaling Coccidioides spores lifted from soil by wind, tilling, harvesting, grading, or digging.
Farmworkers and Construction Crews Carry the Heaviest Exposure
Risk is not evenly distributed, and the study points to why. The people who move soil are the people who breathe the dust first. Agricultural laborers, equipment operators, construction and solar site crews, groundskeepers, and wildland firefighters all face concentrated exposure in endemic counties. Residents living beside those operations face a second, lower tier of exposure carried on the wind.
Severity risk follows a different pattern. Many people who inhale the spores never develop symptoms, and most who do recover. A small share of infections become severe, spreading beyond the lungs or causing serious long-term lung disease. The California Department of Public Health reports that about 1,000 Californians are hospitalized for Valley fever each year and that roughly one in ten of those hospitalized patients dies. People at higher risk for severe illness include adults over 60, people who are pregnant, people with diabetes or weakened immune systems, and Black and Filipino patients.
The state's case burden has climbed sharply. Rates have risen more than 800 percent over the past two decades. California reported 7,000 to 9,000 cases annually from 2017 through 2023, then nearly 12,500 in 2024, the highest annual figure on record.
Association, Not Proof, and the Limits of the New Analysis
This is an observational study, and its authors are direct about what it cannot show. Comparing residential addresses against land cover cannot prove that a particular landscape causes infection. People may have been exposed at a worksite, on a road, or during travel rather than near home. The analysis also cannot quantify how much additional risk a specific fallowed field creates for a specific town. The researchers say future work should sample soils directly to determine where the fungus actually grows.
Current medical guidance has not changed as a result of this work. What the study adds is a plausible and testable mechanism, plus practical targets the authors name: dust control on idled and recently retired fields, air quality warnings during high-risk seasons, and respiratory protection such as N95 masks for outdoor workers. The work was funded by the National Institutes of Health and a University of California research program, and the authors declared no competing interests.
Alexandra Heaney, an assistant professor at the Herbert Wertheim School of Public Health and Human Longevity Science at UC San Diego and the study's first author, framed the stakes in a university news release, saying that "California is undergoing a major transformation of its agricultural landscape" and that the health effects of that shift need to be understood. Senior author Justin Remais of UC Berkeley added that public health consequences should be weighed alongside the environmental and economic effects as the state adapts to water scarcity.
Symptoms That Should Prompt a Cocci Test in Endemic Counties
Valley fever resembles ordinary pneumonia, which is why it is often missed. Cough, fever, chest pain, fatigue, headache, night sweats, muscle aches, and a rash are common presentations and can persist for weeks. The illness is diagnosed via a blood test, which must be ordered specifically.
Residents of Fresno, Kern, Kings, Tulare, Madera, San Luis Obispo, Monterey, and neighboring counties who develop a respiratory illness that does not improve after 7 to 10 days can ask a clinician directly whether Valley fever testing is warranted. MedicalDaily recently reported on hospital data showing how often that test is never ordered in endemic areas.
Practical precautions are modest and evidence-based. Outdoor workers can use fitted respiratory protection and wet down soil before disturbing it. Drivers can keep windows closed and use recirculated air during dust storms. Anyone whose symptoms worsen, who develops shortness of breath or chest pain, or who has a weakened immune system should seek prompt medical evaluation rather than waiting it out. County health departments and the state's Valley fever information page publish current local guidance, and updated state case counts are expected through the fall.
Key Questions Answered
What did the new study find? Communities surrounded by shrubland, barren ground, grassland, certain crop types, and newly fallowed fields showed higher Valley fever incidence across 20 California counties, based on 65,657 confirmed cases. Orchards, produce, and rice were associated with a lower incidence.
Does this mean farmland causes Valley fever? No. The study is observational and shows only an association. Patients may have been exposed away from home, and the analysis cannot measure how much risk any single field adds.
Who faces the greatest exposure? People who disturb soil for work, including farmworkers, construction and solar crews, equipment operators, groundskeepers and wildland firefighters, plus residents living close to those operations in endemic counties.
Who is most likely to become seriously ill? Adults over 60, people who are pregnant, people with diabetes or weakened immune systems, and Black and Filipino patients face elevated risk of severe disease. Most infections remain mild or produce no symptoms at all.
What symptoms should prompt a call to a clinician? Cough, fever, chest pain, fatigue, headache, night sweats, and rash that persist beyond 7 to 10 days or worsen, particularly after time spent outdoors in endemic areas. Shortness of breath or chest pain warrants prompt evaluation.
Can Valley fever spread from person to person? No. It is acquired by inhaling fungal spores from disturbed soil and dust. It does not transmit between people.
What practical steps reduce exposure? Fitted respiratory protection for outdoor work, wetting soil before disturbing it, keeping vehicle windows closed with recirculated air during dust storms, and asking specifically about Valley fever testing when a respiratory illness is not resolving.
