The mysterious rise of Valley Fever

Digging in parched dirt or simply breathing in dry air is not without peril in certain parts of the Southwest, where a fungus called Coccidioides is known to infect many who inhale its spores, sickening an increasing number of people over the past decade and a half.

The resulting illness called Valley fever – while often mild – can cause lingering flu-like symptoms and even lead to chronic illness when it spreads to other parts of the body, sometimes triggering life-threatening complications, like meningitis.

"In cases where it gets into the brain and into the spinal cord, it can be very challenging to treat," sometimes requiring lifelong therapy or even causing death, says Dr. Tom Chiller, a medical officer and deputy chief of the Centers for Disease Control and Prevention's Mycotic Diseases Branch, which is dedicated to preventing death and disability from fungal diseases. Fortunately, Valley fever is rarely deadly, with fewer than 200 deaths attributed to it annually. But Chiller notes that it's currently one of the most common infectious diseases in Arizona. It's also common in California, including in the San Joaquin Valley, from which Valley fever derives its name, as well as Nevada, Texas and lower Utah, afflicting thousands of residents through the air as well as workers who disturb the soil where the Coccidioides fungus grows.

A report published online this month in the CDC's Emerging Infectious Diseases journal spotlighted an outbreak involving Valley fever that affected at least 44 workers constructing two solar power farms in California's San Luis Obispo County between 2011 and 2014. Those affected did work ranging from digging to electrical, which often put them in proximity to fungal spores that can be breathed in, and cause infection. The workers reported symptoms ranging from fatigue and night sweats to fever, difficulty breathing, joint and muscle pain and weight loss. Most needed to take time off from work and, for two, the disease spread elsewhere in their bodies – to the skin of one individual and the bones of another.

"The area is endemic of Coccidioides – that means that the fungus that causes Valley fever grows in this area. It's found in the soil," says Jason Wilken, lead author of the report and a field officer for the CDC assigned to the California Department of Public Health. "This large-scale solar farm construction involves quite a bit of soil disturbance – from grading and digging trenches and so forth. People are exposed by just being at the site, or they might have job duties that result in greater exposure, such as electricians working in trenches." Half a dozen companies involved in the construction of the solar farms were also cited by the state's Division of Occupational Safety, Cal/OSHA, for not doing enough to safeguard workers, like limiting exposure to high levels of dust.

Nor is construction likely to decrease in California, says Wilken, noting the need to protect workers in certain arid regions, who are at much higher risk of developing Valley fever. Residents, too, in endemic areas face risk of infection, and the number of confirmed cases of Valley fever has grown significantly.

In total, the prevalence of Valley fever in Arizona and California and other states​ climbed from 2,271 reported cases in 1998 to peak at 22,641 cases​ reported in 2011. Though reporting mechanisms change, which the agency allows can affect totals, Chiller believes the increase is real, and factors ranging from climate – such as periods of drought followed by rain, which allows fungi to thrive and spores to be spread – to people relocating to areas where Coccidioides exists, could have driven the increase.

Experts also note that the actual number of people who get Valley fever far exceeds reported case totals, since many don't exhibit symptoms and recover without medical attention. As a result, the CDC is working on a way to estimate the true prevalence of the disease. In more recent years, Valley fever cases have dipped to 8,232 reported last year. And based on 2013 and 2014 numbers and preliminary data from 2015, the number of cases seems to be leveling off, Chiller says – though​ it could increase again in the future.​

The CDC did confirm a handful of cases several years ago in Washington state. But whether the disease's footprint is growing – and, if so, to what extent – requires further evaluation.

What health experts do know is that early detection and treatment of Valley fever can improve outcomes for patients with the severest cases, and reduce their likelihood of developing chronic disease.​

Dr. Kathleen Jordan,​ an infectious disease specialist with Dignity Health, based in San Francisco, says she's concerned by an increase in the number of people diagnosed with Valley fever over the past decade.​

Experts speculate that numerous factors could be driving up the number of infections observed in arid climates, where Coccidioides thrives. But whether the prolonged drought in the West could further increase the prevalence of Valley fever is up for debate, since fungi do need water to grow, in addition to the lift spores get from dry, windy conditions.

"There's many people that hypothesize why that is happening ... [from] more travel, increase in population, increase in proximity to the desert. There's more immunosuppressed patients, as we see more HIV and more organ transplant and more people on steroids. Economic stressors have caused people to move around more, so you're getting more people exposed. So, I wouldn't simply just say that the weather alone is the only thing causing us to have more concern."

Whatever the reason, the total number of Valley fever cases reported annually remains nearly quadruple that reported in 1998. And experts ​say it's important for those who live and work in or travel to areas where the fungus thrives to see a doctor if they experience lingering flu-like symptoms characteristic of Valley fever, and to voice concerns if they believe they could have contracted it.

"The majority of patients that are exposed to Coccidioidomycosis do very well. Forty percent will not recall any symptoms," Jordan says, and most who do recover without treatment, she adds.

However, according to the CDC, some at risk for severe Valley fever will require longer-term treatment with antifungal medication. It's the almost 1 percent of patients at risk for severe cases that spread and cause chronic, sometimes life-threatening issues that most concern doctors. "Those are the patients we obviously are worried about," Jordan says. "We'd like to identify them early and treat them early."

Copyright 2015 U.S. News & World Report

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