Sources of Valley Fever (Coccidioidomycosis)

Areas Endemic for Coccidioidomycosis

This map is based on studies performed in the late 1940s and 1950s and also on locations of more recent outbreaks and cases. Coccidioides might also live in similar areas with hot, dry climates that are not shaded on the map.

Where does Coccidioides live?

Coccidioides lives in dust and soil in some areas in the southwestern United States, Mexico, and South America. In the United States, Coccidioides lives in Arizona, California, Nevada, New Mexico, Texas, and Utah. The fungus was also recently found in south-central Washington.1

Additional Information about geographic range of Coccidioides


Life Cycle of Coccidioides

Coccidioides spores circulate in the air after contaminated soil and dust are disturbed by humans, animals, or the weather. The spores are too small to see without a microscope. When people breathe in the spores, they are at risk for developing Valley fever. After the spores enter the lungs, the person’s body temperature allows the spores to change shape and grow into spherules. When the spherules get large enough, they break open and releases smaller pieces (called endospores) which can then potentially spread within the lungs or to other organs and grow into new spherules.

Figure showing the biology of Coccidioidomycosis

PDF version of imageCdc-pdf [PDF – 1 page] for printing.


Uncommon sources of Valley fever

The most common way for someone to get Valley fever is by inhaling Coccidioides spores that are in the air. In extremely rare cases, people can get the infection from other sources, such as:

  • From an organ transplant if the organ donor had Valley fever7
  • From inhaling spores from a wound infected with Coccidioides8
  • From contact with objects (such as rocks or shoes) that have been contaminated with Coccidioides9, 10


Testing Soil

Testing soil for Coccidioides is sometimes done as a research activity

Testing soil for Coccidioides is sometimes done as a research activity.

I’m worried that Coccidioides is in the soil near my home. Can someone test the soil to find out if the fungus is there?
No, in this situation, testing soil for Coccidioides isn’t likely to be useful because the fungus is thought to be common in the soil in certain areas. A soil sample that tests positive for Coccidioides doesn’t necessarily mean that the soil will release the fungus into the air and cause infection. Also, there are no commercially-available tests to detect Coccidioides in soil. Testing soil for Coccidioides is currently only done for scientific research.

Testing soil for research
Scientists sometimes test soil or other environmental samples for Coccidioides to understand more about its habitat and how weather or climate patterns may affect its growth. The available methods to detect Coccidioides in the soil don’t always detect Coccidioides spores even if they are present. However, new tests are being developed so that researchers can better detect Coccidioides in the environment.

Click here to learn more about how CDC is using advanced molecular detection (AMD) methods to better understand the geographic distribution of Coccidioides.

Valley Fever and the weather

Scientists continue to study how weather and climate patterns affect the habitat of the fungus that causes Valley fever. Coccidioides is thought to grow best in soil after heavy rainfall and then disperse into the air most effectively during hot, dry conditions.11 For example, hot and dry weather conditions have been shown to correlate with an increase in the number of Valley fever cases in Arizona12 and in California (but to a lesser extent).13 The ways in which climate change may be affecting the number of Valley fever infections, as well as the geographic range of Coccidioides, isn’t known yet, but is a subject for further research.

Geographic range of Valley fever expands to Washington State

Scientists believed that Coccidioides only lived in the Southwestern United States and parts of Latin America until discovering it in south-central Washington in 2013 after several residents developed Valley fever without recent travel to areas where the fungus is known to live. Samples from one patient and soil from the suspected exposure site were analyzed using a laboratory technique called whole genome sequencing and were found to be identical, proving that the infection was acquired in Washington.

After this discovery, many unanswered questions remain: How widespread is Coccidioides in Washington? How did it get there? How long has it been living there? Information about where a person was most likely infected with Valley fever, how strains are related, and which areas could pose a risk is essential for raising awareness about the disease among public health officials, healthcare providers, and the public. CDC is working with state and local public health officials and other agencies to better understand where the fungus lives so that healthcare providers and the public can be aware of the risk for Valley fever.

Next: Learn about the diagnosis and testing of Valley Fever >

  1. Marsden-Haug N, Goldoft M, Ralston C, Limaye AP, Chua J, Hill H, et al. Coccidioidomycosis acquired in Washington State. Clin Infect Dis. 2013 Mar;56(6):847-50.
  2. Edwards PQ, Palmer CE. Prevalence of sensitivity to coccidioidin, with special reference to specific and nonspecific reactions to coccidioidin and to histoplasmin. Diseases of the chest. 1957 Jan;31(1):35-60.
  3. Werner SB, Pappagianis D. Coccidioidomycosis in Northern California. An outbreak among archeology students near Red Bluff. California medicine. 1973 Sep;119(3):16-20.
  4. Werner SB, Pappagianis D, Heindl I, Mickel A. An epidemic of coccidioidomycosis among archeology students in northern California. N Engl J Med. 1972 Mar 9;286(10):507-12.
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  6. Hector RF, Laniado-Laborin R. Coccidioidomycosis–a fungal disease of the Americas. PLoS medicine. 2005 Jan;2(1):e2.
  7. Dierberg KL, Marr KA, Subramanian A, Nace H, Desai N, Locke JE, et al. Donor-derived organ transplant transmission of coccidioidomycosis. Transpl Infect Dis. 2012 Jun;14(3):300-4.
  8. Eckmann BH, Schaefer GL, Huppert M. Bedside Interhuman Transmission of Coccidioidomycosis Via Growth on Fomites. An Epidemic Involving Six Persons. Am Rev Respir Dis. 1964 Feb;89:175-85.
  9. Dweik M, Baethge BA, Duarte AG. Coccidioidomycosis pneumonia in a nonendemic area associated with infliximab. South Med J. 2007 May;100(5):517-8.
  10. Stagliano D, Epstein J, Hickey P. Fomite-transmitted coccidioidomycosis in an immunocompromised child. Ped Infect Dis J. 2007 May;26(5):454-6.
  11. Smith CE, Beard RR, et al. Effect of season and dust control on coccidioidomycosis. JAMA. 1946 Dec 7;132(14):833-8.
  12. Park BJ, Sigel K, Vaz V, Komatsu K, McRill C, Phelan M, et al. An epidemic of coccidioidomycosis in Arizona associated with climatic changes, 1998-2001. J Infect Dis. 2005 Jun 1;191(11):1981-7.
  13. Zender CS, Talamantes J. Climate controls on valley fever incidence in Kern County, California. Int J Biometerol. 2006 Jan;50(3):174-82.