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Valley fever—a potentially devastating fungal infection—has surged dramatically in California over the past 25 years. According to a recent report from the California Department of Public Health, cases are on track this year to exceed last year’s record high of more than 12,500 diagnoses. This marks a staggering increase of over 1,200% since 2000 when reported cases numbered fewer than 1,000 in the state.
Valley fever is caused by inhaling spores of the naturally occurring fungus Coccidioides, common in soil in certain California regions. When dry conditions lift spores into the air, people who breathe them in can become infected. Although most people experience mild or no symptoms, the disease can cause severe illness and even death in some cases.
Shaun Yang, director of molecular microbiology and pathogen genomics at UCLA’s Department of Pathology and Laboratory Medicine, explained that a pattern of mild, wet winters followed by dry spells has created ideal conditions for fungal growth underground, where frost no longer kills it off. “This kind of very wet and dry pattern definitely is perfect for this fungus to grow,” Yang told SFGATE.
Experts attribute the dramatic rise in cases largely to climate change, which intensifies periods of drought and rainfall. These fluctuations increase the fungal growth cycle and the likelihood that spores spread when dry soil is disturbed by wind, construction, or agriculture. “I think climate change is the main reason to explain this type of dramatic explosion,” Yang said.
The infection can result in symptoms such as severe fatigue, cough, fever, night sweats, and muscle pain, lasting weeks to months. In severe cases, spores disseminate beyond the lungs to bones, brain, or skin, requiring lifelong antifungal treatment. About one in ten hospitalized patients with Valley fever die from the disease, underscoring its potential severity.
Children can be especially vulnerable, with severe cases affecting bones and requiring chronic care. “They’re not going to live normally,” Yang emphasized.
Dr. John Galgiani, director of the University of Arizona Valley Fever Center for Excellence, noted that part of the rise in reported cases may reflect changes in case reporting protocols rather than a pure increase in disease incidence. Previously, health officials had to confirm symptoms before reporting a case; this requirement has been relaxed, potentially inflating recent numbers. However, Galgiani concurred that climate change likely expands the range of Valley fever beyond its traditional zones, potentially reaching across western U.S. regions up to the Canadian border.
Certain populations face higher risk of serious illness, including agricultural and construction workers in endemic areas, people over 60, pregnant individuals, people with diabetes, and those with compromised immune systems. Early testing is advised for those in or visiting known endemic regions who develop symptoms resembling pneumonia.
From a public health perspective, the rapid rise of Valley fever cases highlights a growing threat driven by environmental changes and underscores the need for awareness, testing, and protective measures in vulnerable populations.
Medical Disclaimer: This article is for informational purposes only and should not be considered medical advice. Always consult with qualified healthcare professionals before making any health-related decisions or changes to your treatment plan. The information presented here is based on current research and expert opinions, which may evolve as new evidence emerges.
References:
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California Department of Public Health, 2025 report on Valley fever case numbers.
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Yang S., UCLA Department of Pathology and Laboratory Medicine, Interview, 2025.
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Galgiani J., University of Arizona Valley Fever Center for Excellence, Interview, 2025.
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SFGATE article: “They’re not going to live normally”: A potentially devastating disease surges in California, August 2025. DOI unavailable.
