Valley fever spread after a California music festival in Bakersfield earlier this summer. Experts warn that cases are becoming more common and might be fueled by climate change. (Chris Boswell/iStock via Getty Images)
Attendees at this month’s foggy, mild Outside Lands might find it hard to believe that climate change could be affecting concerts, but an early summer music festival in Bakersfield resulted in a handful of cases of an illness that experts believe is spreading more due to the state’s changing weather patterns.
Valley fever is a respiratory disease caused by coccidioides or “cocci,” a soil-dwelling fungus found in California and the southwestern U.S. When contaminated soil is disturbed, infectious spores are released into the air and can be inhaled by people and animals. Once inhaled, cocci can infect the lungs, leading to symptoms such as cough, fever, chest pain and fatigue, according to the California Department of Public Health.
While valley fever has been present in the western United States for years, its incidence rate is increasing. The number of cases has tripled between 2014 and 2018 and again between 2018 and 2022, according to new research funded by the National Institutes of Health. In the past 20 years, the rate of infection has increased by 800%.
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By June 2024, more than 5,300 people in California have contracted the disease this year, including five who experienced symptoms after attending Bakersfield’s Lightning in a Bottle festival in May. The California Department of Public Health warned that these cases “occurred among people who traveled through Kern County, California, to attend the outdoor music festival.”
Climate and health experts believe that changing climate conditions contribute to the increase.
“We’ve had really the perfect conditions for the spread of coccidioides,” said Dr. George Thompson, a professor of medicine at UC Davis Medical Center in Sacramento. “The sort of cycle of precipitation and drought we’ve had really has favored the growth of coccidioides in the soil and then spread during and following periods of drought.”
State health officials say California is on track to have more valley fever cases this year than ever before – including a notable uptick in the Bay Area – likely resulting in part from climate change. Source: California Department of Public Health (Chart by Kara Newhouse/KQED)
The idea that drought could increase the number of valley fever cases is somewhat counterintuitive since it seems to dampen infection peaks in the short term.
However, Alexandra Heaney, an assistant professor of public health at UC San Diego and an author of the recent study, emphasized that her research indicated that drought increases the total number of cases in the long term.
“We think that there’s this sort of primary driver, which is wet conditions, followed by dry conditions, [that] leads to an increase in cases,” she said.
She and her co-authors hypothesize that wet, rainy periods promote extensive fungus growth, followed by dry spells that allow the fungus to form and release infectious spores into the air. Cocci can also withstand dryer, harsher conditions — allowing it to outlast much of its competition during droughts.
Another potential link between drought and valley fever is its impact on rodent populations, which serve as a nutrient source for the fungus. According to a release, Heaney and the team’s research suggests that during droughts, declining rodent populations lead to a “corresponding increase in rodent decomposition” and “may supply the necessary nutrients and moisture for the fungus to survive and spread in drought conditions.”
Drought also heightens the risk of wildfires, which can carry and spread infectious spores through smoke.
“Fire is going to follow droughts, just like valley fever follows droughts,” Thompson said. He explained that fires can create wind and updrafts that pull soil and particulate matter from the soil up into the air.
While the risk of infection remains low for most people, and valley fever is not transmitted from person to person, Heaney said that as climate change continues to alter California’s weather patterns, it could further accelerate the spread of the disease.
“Our evidence shows that these severe swings between really wet and really dry conditions tend to actually promote risk for the disease,” Heaney said. “And if this is going to continue to become more common due to climate change, it’s something that might be contributing to the increases we’ve seen and may actually promote increases in the future as well.”
