Those who frequently work in dry, dusty fields or construction sites are most at risk.

Nationally, the number of cases reported has risen 850 percent since 1998. California and Arizona have been hit hard in recent years, especially in farm regions, with Arizona alone seeing 16,400 cases last year.

A fungal spore transported through the air causes valley fever. The illness enters the body when infected dust is inhaled. When a year or two of rain is followed by dry and windy conditions, the fungus growth is accelerated before drying and being spread on the breeze.

Unfortunately, those conditions describe the situation in the West this year.

According to an AP article, the Center for Disease Control said:

An estimated 150,000 valley fever infections go undiagnosed every year. That's because valley fever is difficult to detect and there's little awareness of the disease, experts say.

The fever often causes mild to severe flu-like symptoms, and in about half the infections, the fungus – called Coccidioides – results in no symptoms. But in a small percent of cases, the infection can spread from the lungs to the brain, bones, skin, even eyes, leading to blindness, skin abscesses, lung failure, even death.