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Valley Fever is Spreading Beyond the Valley

Coccidioidomycosis, also known as valley fever, is an infection caused by inhalation of Coccidioides immitis spores. Coccidioides is a soil-dwelling fungus that is endemic to arid regions of Mexico, Central and South America, and the southwestern United States. Arizona’s Sonoran Desert, which includes the metropolitan areas of Phoenix and Tucson, and California’s southern San Joaquin Valley are particularly high-risk areas and have traditionally accounted for 95% of cases in the United States. Coccidioides has also occured to a lesser extent in Nevada, New Mexico, Utah, and Texas.

In 2023, the California Department of Public Health recorded 9,280 new cases of Valley fever, which was the highest number of cases ever documented. Coccidioides spores have spread into Southern and Northern California and even into parts of Oregon and Washington. This surge of cases has been attributed to climate change and the atmospheric rivers that have been dumping record amounts of rain and snow on California and the Pacific Northwest. Coccidioides thrives in a rain-drought cycle–when conditions swing from extreme dryness to extreme wetness.


Teirstein Z and Grist, Valley Fever Cases Surge after California’s Atmospheric River Downpour, Scientific American, Feb 16, 2024.

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