California is heading toward another record year for cases of Valley fever, the disease caused by fungal spores linked to cycles of drought and precipitation.
There were 3,123 reported cases of Valley fever in the first three months of the year, according to state health officials — roughly double the 10-year average for the first-quarter time period. Cases ranged from a low of 801 in 2016 to 3,011 last year.
Most people who are infected with the fungus won’t experience symptoms, and their bodies will fight off the infection naturally. Those who do suffer symptoms however are often hard-pressed to recognize them, as they resemble the onset of COVID or the flu, further complicating efforts to address the disease.
The disease is caused by inhaling spores of coccidioides, a fungal pathogen that thrives in the drier and dustier regions of the state. The fungus is released when the dry soil where it grows is disturbed.
“We actually had sort of seen this coming, just based on the climate cycle of the last few years,” said George R. Thompson, a professor of medicine at the UC Davis School of Medicine and a specialist in invasive fungal infections.
Research has shown that patterns of drought and precipitation play important roles in the number of Valley fever cases in California, said Doua Ge Yang, a spokeswoman for the state’s Department of Public Health. “When there are several years of drought in California, followed by a wet winter, and then a dry summer,” there are increases in the Valley fever cases for the following two years.
She said 2023 typified such a scenario, and as predicted, 2024 resulted in a record-high case count, with 12,637 cases recorded.
“Valley fever is on the rise in California,” she said.
While the numbers for 2025 are so far higher than any previously recorded first quarter, Yang said health officials can’t predict whether it will remain a record year. She also noted that all the numbers from 2024 and 2025 are considered preliminary — and therefore demographic issues such as age, sex and race cannot yet be reported.
In addition to patterns of rain and drought, research shows that other factors can play a role in incidents of Valley fever — including soil disturbance, such as the kind accompanying construction activity, wild fires and even archaeological digs.
Construction workers, firefighters and archaeologists working in the dry, arid regions of the state are at increased risk of getting the disease — especially as Californians move into these once less inhabited regions of the state.
Last year, at least 19 people who attended Lightning in a Bottle, a five-day music and art festival held at Buena Vista lake in Kern County, succumbed to the disease — including several who reported severe disease, which included pneumonia-like symptoms, rashes, headaches and exhaustion.
The festival’s organizers will be holding the event again this year at the same location. According to the festival website, organizers will try to reduce dust by applying water to the ground to keep it in place, adding artificial turf in front of the stages for dancing, and reducing the number of motorized vehicles used by staff around the site, and placing additional wood chips over heavy traffic areas to suppress dust.
Because most people clear the disease on their own, the true number of infected people is not known. However, if a person’s immune system is unable to clear the disease, and it is left untreated, it can cause death or permanent disability.
Treatment varies depending upon severity, but antifungal drugs, such as fluconazole (Diflucan) or itraconazole (Sporanox, Tolsura), are the most common medications. However, they come with serious side effects, such as nausea, vomiting, diarrhea, hair loss, dry skin, dry mouth and chapped lips.
While several Central and Southern California counties have seen recent increases in their case counts, Monterey’s numbers have ballooned.
In 2023, there were 22 cases reported during the first quarter in the Central California county; this year, the number is 217.
County health officials said they began seeing a surge in November of last year, at which point they sent out a health advisory to local medical providers and clinics providing information about the disease and testing guidance.
Monterey County spokeswoman Karen Smith said that many residents had experienced severe disease and delays in their treatment and diagnosis. She said rates were highest for people who live in the southern part of the county and in the largely agricultural Salinas Valley.
She said the county encourages people to reduce their risk of getting the disease by avoiding breathing in dirt and dust.
Thompson, the UC Davis doctor and researcher, said there has been anecdotal evidence that the disease may be increasing in severity, and there are concerns that it may also have acquired some immunity to the common antifungal medicines used to fight it.
The theory is that the widespread use of antifungal chemicals on crops in areas where the fungus is endemic may be contributing to its resistance, but that research on the topic is only just getting underway, and answers so far are elusive.
He said there’s a statewide effort looking into these issues, that includes participation from the U.S. Centers for Disease Control and Prevention, the state’s public health department, UC Davis, UC San Francisco, and Cal State Fresno and Cal State Bakersfield.
He said for years the disease had largely been sidelined in public health circles as attention and funding was targeted at other pathogens that had wider and more severe impacts.
“I hate to disparage that, but I think with limited resources, public health agencies do have to really prioritize certain pathogens,” he said.
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