New research links surge in Valley fever cases reported in California to droughts

SAN DIEGO (FOX 5/KUSI) — Valley fever, a dangerous disease brought on by inhaling dust carrying fungus spores, has seen a dramatic increase in the number of reported cases in California over the last decade.

According to the California Department of Public Health , the number of cases have concerningly tripled two times in the last decade — first during the period between 2014 and 2018, and then again between 2018 and 2022 — despite remaining relatively rare.

Scientists have largely linked this endemic increase to more swings from extreme drought to immense precipitation amid climate change that have created ideal conditions for the fungus that causes Valley Fever, the Coccidioides fungus, to grow and spread.

New research from UC San Diego and UC Berkeley backs this understanding and offers critical insight for public health officials to better prepare for future upticks in Valley fever cases.

“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,” one of the study’s authors, UC Berkeley School of Public Health professor Dr. Justin Remais, said in a statement.

The study, which was published in the October edition of The Lancet Regional Health – Americas, compared the number of Valley fever cases with seasonal climate data to understand how disease cycles are influenced by periods of drought periods.

According to UCSD researchers, looking at health data in this way found that Valley fever cycles seasonally with most cases reported during the three months between September and November.

However, there was some fluctuation observed with the peaks across counties and depending on whether that area is experiencing drought conditions.

Generally, Valley fever is contracted when people inhale infectious spores of the fungus that become aerosolized when soil is disturbed by wind or human activity. The onset of symptoms usually occurs weeks after this contact, researchers note.

Counties in the San Joaquin Valley and Central Coast see more cases of Valley fever on average and experience the most pronounced seasonal peaks, but periods after drought conditions ease see a heightened presence of the disease.

As researchers explained, the outsized impact of Valley fever when minimal drought conditions are present is likely caused by the soil-dwelling fungi’s growth spurred by renewed precipitation.

Unlike other types of fungi, Coccidioides has a greater capacity to survive hot conditions like droughts, in part because its spores are heat-resistant and due to spikes in rodent deaths during these periods — rodents are thought to be an important source of nutrients for the fungus.

Despite remaining more dormant in these periods, the survival of the fungus spores in drought allows for it to proliferate more widely with less competition for nutrients when rain returns.

“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,” said Dr. Alexandra Heaney, assistant professor at UCSD’s Herbert Wertheim School of Public Health and Human Longevity Science who co-authored the study.

Researchers hope this new understanding will help Californians and public health officials better prepare for heightened periods of Valley fever infections through awareness on when and how people can become at risk.

When left untreated, the respiratory disease can spread and cause damage to other parts of the body, such as the skin and bones. In some cases, the brain can also be impacted, which can be deadly.

To prevent infection, health officials encourage limiting outdoor time when it is dry and dusty, periods where there is likely a heightened presence of the spores in the air. Wearing a face mask covering capable of blocking dust while outside is also urged for those in at-risk areas.

“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,” Remais said.

For the latest news, weather, sports, and streaming video, head to YourCentralValley.com | KSEE24 and CBS47.