Construction workers are getting sick with valley fever in Riverside County. Why are cases up?

Construction workers should keep an eye on their health in Riverside County.

The area is on track to have more people sick with valley fever than last year, according to public health officials, who want residents to be on alert now because the peak of the season is still ahead.

Valley fever has been steadily rising in the county and across the state over the last decade. It’s typically associated with the Central Valley, but it does show up in Southern California’s urban areas. Here’s what you should know.

What is Valley Fever?

 Valley fever is a respiratory disease that’s caused by the Coccidioides fungus, a natural organism that grows in some soil and dirt areas. People who work or spend time in dusty environments are most at risk.

The disease is caught by inhaling spores that have been kicked up in the wind. Symptoms are very similar to pneumonia, said Wendy Hetherington, chief epidemiologist of Riverside University Health System. That can include fever, cough, chest pain, fatigue and shortness of breath.

Dust is kicked up for valley fever research in Santa Margarita.

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Carolyn Van Houten

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The Washington Post via Getty Images

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These usually take one to three weeks to develop after exposure, which is why Hetherington says the department wanted to notify the public and hospitals now.

“ We see sort of the seasonal peaks… in November and December,” Hetherington said. “That's because of the delay from exposure, to symptom onset, to diagnosis.”

Other noticeable changes can happen, such as weight loss, rashes or muscle pain, according to the California Department of Public Health.

Symptoms usually resolve on their own in a few weeks, but some could go as long as a few months. In rare cases, valley fever causes infections in other parts of the body. Adults over 60, those with chronic health conditions, or weakened immune systems are at higher risk for severe infections.

What’s the situation now?

Riverside County has seen a 58% rise in cases compared to the same period last year.

As of July 31, 322 people in the county have a suspected, probable or confirmed case of valley fever. This is when all counties report provisional mid-year data to the state.

Hetherington said their data show most cases are coming from the county’s northwestern urban areas of Riverside and Corona. They’ve interviewed some of the diagnosed people to learn more about how they got infected.

“ What we see is when an occupation is provided… particularly in our region, it’s construction,” Hetherington said.

Thirty-six percent of people interviewed worked outdoors, according to the county. More than half had a co-existing condition, such as diabetes.

What’s driving it?

Riverside’s jump in cases so far mirror what’s going on in other parts of the state. The county is in the middle range of valley fever cases, but most infections are found in Central California hot spots.

Case rates overall have been going up for years. California reported nearly 12,500 cases in 2024, the highest number on record for the state.

Hetherington said the leading theory is that it’s being caused by climate change, in particular through increases in drought and heat.

“ Not only that, but it’s the heavy rains followed by drought, which seems to be the thought of what is causing the increase,” she said. “That stirs up the air and then the dryness makes the dust blow around more and people are exposed.”

Other factors are likely driving the increase, too. For example, high winds have been shown to cause dust storms that spread the spores. After the 1994 Northridge earthquake, researchers linked a valley fever outbreak in Simi Valley to the Santa Ana winds, according to the California Office of Environmental Health Hazard Assessment. The office says it’s also historically been underdiagnosed and under-reported because the symptoms are similar to illnesses like the flu and coronavirus.