Health officials at the Centers for Disease Control and Prevention in Atlanta said cases of Valley Fever, or Coccidioidomycosis, in Arizona, California, Nevada, New Mexico and Utah rose from 2,265 in 1998 to more than 22,000 in 2011.
Valley Fever is caused by inhaling a fungus called Coccidioides, which lives in the soil in the southwestern United States.
Not everyone who is exposed to the fungus gets sick, but those who do typically have flu-like symptoms that can last for weeks or months and more than 40 percent of patients who get ill from Valley Fever may require hospitalization at some point, with an average cost of nearly $50,000 per hospital visit, officials said.
"Valley Fever is causing real health problems for many people living in the southwestern United States," Dr. Tom Frieden, director of the CDC, said in a statement.
"Because fungus particles spread through the air, it's nearly impossible to completely avoid exposure to this fungus in these hardest-hit states. It's important that people be aware of Valley Fever if they live in or have traveled to the southwest United States."