Valley Fever

Valley fever, also known as San Joaquin valley fever, and San Joaquin fever— or by its medical name, Coccidioidomycosis (kok-sih-dee-oyd-o-my-KO-sis)— is a disease that can occur after breathing in the spores * of a fungus found naturally in the soil of dry regions, such as the southwestern United States.

The large red spot on the patient's forearm is the result of a positive skin test for exposure to the Coccidioides spp. fungal organism that causes valley fever (coccidioidomycosis).

The large red spot on the patient's forearm is the result of a positive skin test for exposure to the Coccidioides spp. fungal organism that causes valley fever (coccidioidomycosis). Most of the cases occur in Arizona, California, Nevada, Utah and New Mexico. It is difficult to avoid exposure to Coccidioides, but people who are at higher risk should try to avoid breathing in large amounts of dust in the southwestern United States.
CDC/Dr. Lucille K. Georg.

What Is Valley Fever?

During World War II, American trainees sent to Arizona and parts of Southern California for flight training took thousands of days of sick leave due to valley fever, a disease caused by Coccidioides immitis (kok-sih-dee-OYD-eez IH-mih-tus), a fungus that hibernates a few inches beneath semidry soil. The common name for the disease, San Joaquin valley fever, comes from the San Joaquin Valley region of California, where the fungus was first identified.

After regular rainfall, the Coccidioides fungus blooms into tiny mold spores. If the soil is stirred by events such as dust storms, earthquakes, farming, excavation, or construction work, these microscopic spores spring into the air, where they are easily breathed into the lungs of people and animals.

Valley fever cannot be passed from person to person. People must inhale the spores of the fungus in order to contract the disease. Most people who inhale the spores develop only a mild case of disease, in which the infection results in symptoms similar to those of a cold or the flu that go away on their own. Many people are not even aware that they are infected when the symptoms are mild. People with weakened immune systems * develop more serious cases. North and Central American people with African, Filipino, or Siberian ancestry are especially susceptible. These populations get more severe forms of valley fever, in which cases it can spread from the lungs to other parts of the body and even to the brain. Severe cases may result in meningitis * . Coccidioides infection that has spread throughout the body and occurs with arthritis (inflammation of the joints) is sometimes called desert rheumatism (ROO-muh-tih-zum). In general, the more fungal spores a person inhales, the more serious the disease tends to be.

Is Valley Fever Common?

The fungus that causes valley fever is found mainly in the desert climates of the southwestern United States, parts of Mexico, and Central and South America. The infection is considered endemic * in these regions. People who live in or visit cocci country and who often spend time outside for work or play are more likely to develop the disease, especially near areas of development and construction during the summer and fall.

Up to 50 percent of people living in such areas have antibodies * against Coccidioides immitis in their blood, which indicates that they have been exposed to the fungus, although many of them never developed signs of the disease. Furthermore, climate changes that bring winds can spread spores and thereby deliver the infection to new geographic areas.

What Are the Symptoms of Valley Fever?

About 60 percent of people infected by Coccidioides immitis develop no symptoms. When symptoms do occur, they are usually mild and include fever, aches, chills, headache, and tiredness. Those with weakened immune systems, such as people with AIDS * , certain types of cancer, and diabetes * , have a greater risk of developing a more severe form of the infection.

How Is Valley Fever Diagnosed?

A doctor diagnoses valley fever by culturing * a patient's sputum * or by doing a skin test. If injecting the test material into the skin of the forearm causes a large circular welt to appear on the arm within two days, it is considered a positive test for the fungus. Blood tests may show antibodies to the fungus, which helps confirm the diagnosis. Examination of lung or skin biopsies * may reveal the fungi. A chest x-ray is sometimes taken to look for signs of infection or inflammation in the lungs.

What Is the Treatment for Valley Fever?

Most mild cases of the disease can be managed with bed rest, over-thecounter pain relievers such as acetaminophen, and sometimes oral (by mouth) antifungal medication (which destroys fungi). In more serious cases in which the fungus has spread throughout the body, intravenous (in-tra-VEE-nus, or given directly into a vein) antifungal medicines and hospitalization may be necessary. Mild cases of valley fever last about two weeks, but recovery may take up to six months in more severe cases.

Pneumonia * , arthritis, meningitis, and other serious problems can result if the infection spreads throughout the lungs or to other parts of the body, such as the liver, heart, brain, bones, or joints.

Can Valley Fever Be Prevented?

No specific activities can prevent a person from becoming infected with the Coccidioides fungus, other than avoiding the regions where it is found. Planting grass and paving roads may reduce dust in problem areas but will not kill the fungus.

See also Fungal Infections • Meningitis • Pneumonia


Books and Articles

Goodyear, Dana. “Death Dust: The Valley-Fever Menace.” New Yorker, January 20, 2014. Available at: (accessed November 10, 2015).

Thomas, Madeleine. “The Mysterious Fungus Infecting the American Southwest.” Atlantic, August 8, 2014. Available at: (accessed November 10, 2015).


Valley Fever Center for Excellence, University of Arizona. “Coccidioidomycosis.” (accessed November 10, 2015).


Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30333. Toll-free: 800-232-4636. Website: (accessed November 10, 2015).

U.S. National Library of Medicine. 8600 Rockville Pike, Bethesda, MD 20894. Toll-free: 888-346-3656. Website: (accessed November 10, 2015).

* spores are a temporarily inactive form of a germ enclosed in a protective shell.

* immune system (im-YOON SIS-tem) the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.

* meningitis (meh-nin-JY-tis) is an inflammation of the meninges, the membranes that surround the brain and the spinal cord. Meningitis is most often caused by infection with a virus or a bacterium.

* endemic (en-DEH-mik) describes a disease or condition that is present in a population or geographic area at all times.

* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.

* AIDS, or acquired immunodeficiency (ih-myoo-no-dih-FIH-shensee) syndrome, is an infection that severely weakens the immune system. It is caused by the human immunodeficiency virus (HIV).

* diabetes (dye-uh-BEE-teez) is a condition in which the body's pancreas does not produce enough insulin or the body cannot use the insulin it makes effectively, resulting in increased levels of sugar in the blood. This can lead to increased urination, dehydration, weight loss, weakness, and a number of other symptoms and complications related to chemical imbalances within the body.

* culturing (KUL-chur) consists of a test in which a sample of fluid or tissue from the body is placed in a dish containing material that supports the growth of certain organisms. Typically, within days the organisms will grow and can be identified.

* sputum (SPYOO-tum) is a substance that contains mucus and other matter coughed out from the lungs, bronchi, and trachea.

* biopsy (BI-op-see) is a test in which a small sample of skin or other body tissue is removed and examined for signs of disease.

* pneumonia (nu-MO-nyah) is an inflammation of the lungs.

  This information is not a tool for self-diagnosis or a substitute for professional care.