Valley fever has been around for more than 100 years, and disproportionately affects poor farmworkers. For some, it becomes a lifelong illness, and doctors don't know why.
Last fall, Kirt Emery was on his motorcycle, cruising up the 99 freeway over the mountains from Santa Barbara to Bakersfield, California, when he saw the dust storm materializing in front of him.

Visibility was low, but he wanted to get through it as quickly as he could, so he held his breath and hammered his bike up to 100 miles per hour.

As the head of epidemiology for the Bakersfield Public Health Services Department, Emery has spent the past two decades studying dust like this - and avoiding it at all costs. He knows all too well what could happen to him if he got sick: the expensive medications with their nasty side affects, the uncertainty of whether he could be ill for the rest of his life.

It's been more than 20 years since he moved to Bakersfield, and so far, he's still healthy. That makes him one of the lucky ones. For many people living in places like Bakersfield, and throughout much of California's Central Valley, dust can be deadly.

Coccidioidomycosis, also known as cocci, or valley fever, is a fungal disease endemic to the soils of the Southwest, in places like Arizona, Nevada, New Mexico, Texas and Utah. In California, it's rampant across the Central Valley, an area just slightly smaller than West Virginia that grows about a third of the country's produce. About 30 percent of all valley fever cases nationwide occur in the Central Valley each year.

Valley fever has perplexed doctors and patients alike for more than a century. Symptoms range from mild fatigue to incapacitating, flesh-eating infections, and despite decades of research, advances in treatment and pushes to develop a vaccine have been painfully slow.

There's virtually no way to guard against inhaling the spores that cause valley fever, as most masks can't filter out the microscopic dust particles that carry the spores through the air and into the lungs. Getting infected with valley fever can be as simple as driving through Bakersfield with the windows down - or in Emery's case, on a motorcycle.

For reasons still unclear, rates of valley fever are rising nationwide. Between 1998 and 2011, documented cases across the country increased steadily by about 15 percent annually, from just 2,000 infections in 1998 to more than 22,000 in 2011. In areas where the fungus is widespread, like Kern County, it's statistically more probable to develop valley fever than hepatitis or chickenpox.

Kern County, where Bakersfield is located, is the world's number one supplier of carrots and grows some of the largest amounts of almonds and pistachios in California, but its soils also have some of the highest levels of cocci fungus in the state. Between 2009 and 2011, valley fever rates tripled there. Researchers blame a population boom that has led to increased construction - which kicks infected soils up into the atmosphere - and unusual weather patterns. As rainy and dry seasons become more erratic due to climate change, rates of valley fever could continue to rise.

Unusually wet years lead to massive cocci blooms in the soil, while subsequent dry spells kick up the spores and render them airborne. Bakersfield is a city covered in dust, fine brown grime kicked up from neighboring farmlands. It streaks windshields and gathers on dashboards, engulfs cars and collects in piles on sidewalks. It's everywhere, and if you live there, it's inescapable.

"You just have to inhale one spore," says George Rutherford, head of the division of preventive medicine and public health at the University of California San Francisco. "The risks of getting a face full of this stuff all depends on where you are, what the climate is."

As valley fever escalates in Kern County, getting the rest of the state to notice, and act, falls heavily on Emery's shoulders. "When you look at how we report cases of cocci here in Kern County and if you ask me what's being done about it, well, there's my secretary out there and there's me.

That's it," he says. "The joke when my secretary retired was that 50 percent of the cocci program went away. Does Kern County invest in cocci? No, they don't."