Valley fever, caused by inhaling dust laced with Coccidioides fungus spores, has spiked dramatically in California over the last decade. According to new research from UC San Diego and UC Berkeley, extreme weather swings—particularly shifts between droughts and heavy rainfall—are responsible for the rise in cases. The fungus thrives in hot, dry conditions and then spreads when disturbed by wind or human activity. Peaks in infections typically occur from September to November, especially in San Joaquin Valley and Central Coast counties.
Dr. Justin Remais, a UC Berkeley professor, highlights that “this is the first study to pin down exactly when disease risk is highest in all of California’s endemic counties, as well as places where the disease is newly emerging.”
Climate Change and the Fungus’ Growth
The study, published in The Lancet, found that while cases dip during droughts, they rise significantly after rain returns. This is due to the fungus’ ability to survive harsh conditions, particularly its heat-resistant spores. The reintroduction of rain spurs fungal growth, allowing it to spread more widely, especially after competition for nutrients declines with the death of rodents during drought periods.
Dr. Alexandra Heaney from UCSD’s Herbert Wertheim School of Public Health explains, “Even though droughts appear to decrease Valley fever cases in the short term, the net effect is an increase in cases over time, particularly as we experience more frequent and severe droughts due to climate change.”
Health Implications and Prevention
Valley fever often presents as a respiratory illness, but when untreated, it can spread to the skin, bones, or even the brain. Public health officials are urging residents in affected areas to limit time outdoors during dry and dusty conditions, as the fungus becomes aerosolized in these periods. Wearing masks capable of filtering dust is highly recommended in areas with heightened spore presence.
For healthcare providers, understanding seasonal patterns will help in diagnosing and treating Valley fever more effectively. As Dr. Remais notes, “Knowing when the Valley fever season starts and how intense it will be can help health care practitioners know when they should be on high alert for new cases.”
Preparing for the Future
As climate change continues to exacerbate extreme weather events, Californians must remain vigilant. Public health officials are now better equipped to predict and respond to Valley fever outbreaks thanks to this research, but individual awareness and preventative actions remain key to reducing the risk of infection.
