Valley fever is contracted by simply breathing in fungus-laced spores from dust blowing in the wind. The disease, which is potentially lethal, has hit California's agricultural heartland particularly hard in recent years, with incidence dramatically increasing in 2010 and 2011.
"Research has shown that when soil is dry and it is windy, more spores are likely to become airborne in endemic areas," said Dr. Gil Chavez, Deputy Director of the Center for Infectious Diseases at the California Department of Public Health.
The symptoms are flu-like, and in some cases, it can spread from the lungs to the brain, bones and skin.
Last week, a federal health official ordered the transfer of more than 3,000 exceptionally vulnerable inmates from two San Joaquin Valley prisons, where several dozen have died of the disease in recent years. A day later, state officials began investigating an outbreak in February that sickened 28 workers at two solar power plants under construction in San Luis Obispo County.
Experts say people who work in Central California dusty fields or construction sites are most at risk to valley fever, as are certain ethnic groups and those with weak immune systems. Newcomers and visitors passing through the region may also be more susceptible.
"Valley fever is a very common problem here, and it devastates people's lives," said Dr. Royce Johnson, professor of medicine at UCLA and chief of infectious diseases at Kern Medical Center. "But many patients don't know about it, and some physicians are only vaguely aware of it because half of our physicians come from out of state."
According to the CDC, valley fever cases in California rose from about 700 in 1998 to more than 5,500 cases reported in 2011. The disease has seen the sharpest rise in Kern County, followed by Kings and Fresno counties.
The Associated Press contributed to this report.