Coccidioidomycosis (cok-SID-EEOY-do-my-ko-sis) is a fungal infection that is also commonly called Valley Fever. It can occur in people with healthy or suppressed immune systems. In people with healthy immune systems, it usually causes mild or moderate lung problems. In people with suppressed immune systems, it can cause serious lung problems and can also spread to other organs, including the bones, joints, lymph nodes, kidneys, or skin. It can also cause disease of the central nervous system, which can be life-threatening if not diagnosed and treated promptly.

Coccidioidomycosis is caused by either of two related fungi, Coccidioides immitis and C. posadasii. These fungi are predominantly found in the southwestern parts of the United States. This includes the central valley of California, Arizona, parts of New Mexico, and Texas west of El Paso. They can also be found in northern Mexico, parts of Central America, and Argentina.

People can become infected with C. immitis and C. posadasii upon breathing in soil or dust contaminated with the fungi. The highest risk of breathing in these fungi is usually during dust storms or natural disasters, most notably in the Southwestern United States. HIV-positive people with CD4 cells below 250 are at the highest risk of developing either mild or severe coccidioidomycosis after breathing in the fungus. Pregnant women and Black and Filipino men are also at a higher risk of developing active disease after being exposed to C. immitis or C. posadasii.