What is valley fever? Cases of fungal infection on upward trend, CDC data shows

(NEXSTAR) – Cases of valley fever, a fungal disease caused by spores found within soil in (mostly) the Southwestern part of the U.S., has been rising in recent decades, prompting warnings from local health authorities.

Last month, the California Department of Public Health put out an alert reminding citizens of “high” case counts and “high” risks of infection in certain parts of the state.

“Valley fever is a serious illness that’s here to stay in California,” CDPH Director and State Public Health Officer Dr. Erica Pan was quoted as saying in a news release issued Aug. 14. “We want to remind Californians, travelers to California, and their healthcare providers to watch for signs and symptoms of Valley fever to help detect it early.”

It’s not just Californians that need to be wary, either. Infections are gradually rising in Arizona, with nearly 11,000 cases in 2023 alone, data from the Centers for Disease Control and Prevention shows. Nevada, New Mexico and Utah are also seeing increased cases, and hundreds more are reported in states further north and east.

What is valley fever?

Valley fever, also known as coccidioidomycosis, is a lung infection that can be contracted by breathing in  spores from a type of fungus called Coccidioides. (There are actually two species of Coccidioides that can cause valley fever, the Mayo Clinic says.) This fungus is found within the soil in certain areas of the U.S., including the Southwest and Pacific Northwest, according to the CDC.

“Wet winters after droughts help the fungus grow,” the CDPH says. Later, when the weather warms up again, the spores may become airborne due to windstorms or construction that disturbs the soil, posing risk for infection, according to the agency.

Climate change, which has expanded the environment where Coccidioides fungus can grow, is also thought to be a factor in rising case numbers, health officials say.

Not everyone who breathes in the fungal spores will become infected. But symptoms of valley fever include fever, coughing, shortness of breath and chest pain, among several others, according to the Mayo Clinic. For this reason, patients with valley fever may mistakenly attribute their symptoms to influenza infection or pneumonia. (Unlike the flu or pneumonia, valley fever does not spread person-to-person, the CDC says.)

“Approximately 5 to 10% of people who get Valley fever will develop serious or long-term problems in their lungs,” the CDC’s website reads.

The infection can also spread to the brain, spinal cord or bones, but only in about 1% of patients, the CDC adds. While “rare,” valley fever that spreads to the brain can be fatal, the Cleveland Clinic says, and approximately 200 people per year are thought to die from it.

Those most at risk of severe symptoms include people with weakened immune systems, those who are pregnant, those who have diabetes, the elderly, and people who are Black or Filipino, the agency says.

Less severe cases of valley fever may clear up on their own, but a healthcare provider may prescribe antifungal medications for more serious cases. A course of antifungal medications can last between three and six months, the Cleveland Clinic’s website explains.

Preventing valley fever, meanwhile, is tricky for those who live in fungal hotspots, but experts recommend using indoor air filtration devices, avoiding construction sites, staying indoors during wind or dust storms, masking up when necessary, and even washing out wounds after coming indoors. (Spores can also cause infection if they enter a break in the skin, health officials say.)

Where is valley fever most common?

While cases of valley fever have been reported in dozens of states, it’s most commonly reported in California and Arizona. In California, there were over 12,000 cases reported in 2024, the CDPH says. In Arizona, there were nearly 11,000 cases in 2023, according to the most recent report from the Arizona Department of Public Health.

Just 25 years ago, both states had reported significantly lower cases of valley fever: specifically, 840 cases were reported in California and 1,917 cases were reported in Arizona in 2000, CDC data shows.

Cases have also been rising in Nevada, New Mexico and Utah, which together reported 566 cases in 2023. All other states where cases have been recorded had collectively reported 555 cases that year. But the fungus is also known to be present in Colorado, Oklahoma, Oregon, Texas, Washington and Wyoming, per a CDC map.

As alarming as these case numbers may seem, the CDC warns that the actual number of cases in the U.S. is “10–18 times” higher than the reported numbers, as many patients may never seek treatment. This also means the CDC believes the annual death toll in the U.S. to be closer to 1,000.

A recent study also determined that dogs, an animal which can also become infected with valley fever, may be able to predict a surge in cases — or a surge in a new area. Researchers at the University of California, Davis, said recent antibody testing data from canines across the country shows a concerning trend.  

“We were … finding cases in states where valley fever is not considered endemic,” lead author Jane Sykes, a professor of veterinary medicine at UC Davis, said. “We should be closely watching those states because there could be under-recognition of the emerging fungal disease in humans.”

Health officials, meanwhile, are urging the public to practice prevention and learn to recognize the symptoms of valley fever to help keep themselves safe.

“Valley fever can be hard to avoid if you live in areas where Coccidioides grows,” reads the Cleveland Clinic website. “Fortunately, most cases aren’t serious and go away on their own.”