Coccidioimycosis (Valley Fever)

Coccidioides immitis endospore. Image by Lucill K. George is in the public domain

Coccidioimycosis is a fungal disease caused by Coccidioides immitis or Coccidioides posadaii, commonly known as "Valley Fever." It is endemic to parts of the Southwest U.S., from Texas to southern California, as well as northern Mexico, Central America, and South America.

While coccidioimycosis generally presents inside the lungs (pulmonary), when it spreads beyond the lungs (extrapulmonary) it is considered an AIDS-defining condition by the U.S. Centers for Disease Control and Prevention (CDC).

Incidence Rate of Coccidioimycosis

According to the CDC, the average incidence rate in the U.S. is 44 persons per 100,000. However, the majority of these cases occur in two states (Arizona, California), where the incidence rate can run as high as 248 per 100,000.

In 2011, over 22,000 new cases of coccidioimycosis were reported by the CDC, a ten-fold increase from 1998. In California alone, the number increased from 719 in 1998 to a high of 5,697 in 2011.

That said, among people with HIV, the incidence of symptomatic coccidioidomycosis has decreased significantly since the advent of combination antiretroviral therapy (cART), while the clinical expression of the disease is seen to be far less severe.

Modes of Transmission

Coccidioides is present in soil where it can develop airborne spores during the rainy season. Infection is caused by inhaling these fungal spores, usually without the person even knowing it.

Once inside the lungs, the spores can produce other spores, which create nodules that can erupt and cause inflammation within the bronchi. In immune-compromised hosts—particularly HIV-infected people with CD4 counts under 250 cells/µL—this can result in often severe pulmonary infections. The fungus can then spread from the lungs into the blood, where it can affect other parts of the body.

Coccidioides is not transmitted from person to person.

Symptoms of Coccidioimycosis

Most infected people don't experience any symptoms or consequences of infection. In those that do, symptoms are usually self-limiting and present with flu-like symptoms such as:

  • Fever
  • Headache
  • Cough
  • Chest pain
  • Shortness of breath
  • Chills
  • Myalgia (muscle pain) and arthralgia (joint pain)
  • Fatigue

A rash can also develop in about 25% of cases. The rash is generally isolated to the lower extremities, typified by tender red nodules or lumps of irregular shape. In some cases (around 5-8%), infection can advance to an uncomplicated community-acquired pneumonia (CAP), which often resolves spontaneously without any specific anti-fungal treatment.

However, in rare cases, coccidioimycosis can be far more severe, causing significant scarring and cavities within the lungs. Once disseminated (i.e. spread beyond the lungs), it can ravage the body, resulting in:

  • Skin ulcers and abscesses
  • Swollen and painful joints
  • Bone lesions
  • Heart inflammation
  • Urinary tract complications
  • Meningitis

Meningitis is the most life-threatening complication of coccidioimycosis. While the overall mortality rate in the U.S. is considered low (0.07%), for those with advanced HIV infection (CD4 under 100 cells/µL), mortality can be as high as 70% even with appropriate treatment.

Diagnosis of Coccidioimycosis

Coccidioimycosis can be diagnosed by microscopic examination of body fluids, sputum, exudates (e.g. pus), or tissue biopsies. Diagnosis can also be made with a PCR (polymerase chain reaction) test, which amplifies DNA from serological samples to confirm Coccidioides infection.

Treatment of Coccidioimycosis

In immune-competent persons with HIV (CD4 over 250 cells/µL), coccidioimycosis is generally self-limiting and requires no specific treatment other than supportive care.

For those requiring treatment—either because of persistent symptoms or progressive disease—oral antifungals are considered the first line choice.

Of these, ketoconazole is the only FDA-approved option for the treatment of coccidioimycosis, although most experts today either fluconazole or itraconazole. (Please note that ketoconazole, fluconazole, and itraconazole are contraindicated during pregnancy and breastfeeding.)

For the severely ill, the antifungal amphotericin B is considered the drug of choice. It is administered intravenously until the infection is controlled, after which life-long oral prophylaxis of either ketoconazole, fluconazole or itraconazole is prescribed.

For patients with coccidioidal meningitis, amphotericin B can be administered intrathecally (i.e. into the space that surrounds either the brain or spinal cord).

Prevention of Coccidioimycosis

It is difficult to prevent coccidioimycosis in endemic areas. For the severely immune compromised, prophylactic therapy may help prevent infection. No vaccines are currently available. If you live an endemic area and believe yourself to be at risk, there are a few precautions you can take:

  • Wear a dust mask when working with soil, or water down the soil to reduce airborne fungus.
  • Avoid going outside during a dust storm or high winds.
  • Use air quality measures, such as a HEPA filter, and install inexpensive window and door seals.
  • If working at a construction site, wear an N95 particle filtering mask.


U.S. Centers for Disease Control and Prevention (CDC). "Increase in Reported Coccidioidomycosis - United States, 1998-2011." Mortality and Morbidity Weekly Report (MMWR). March 29, 2013: 62(12):217-221.

Galgiani, J. "Coccidioimycosis." Journal of the Royal Society of Tropical Medicine and Hygiene. 2005; 41(9):1217-1223.

Pickering, L.; Baker, C.; Kimberlin, D; et al. "Coccidioimycosis." American Academy of Pediatrics, Red Book: 2009 Report to the Committee on Infectious Diseases. Elk Grove Village, Illinois; 28th Edition:266-268.

Masannat, F. and Ampel, M. "Coccidioidomycosis in Patients with HIV-1 Infection in the Era of Potent Antiretroviral Therapy." Clinical Infectious Diseases. January 2010; 50:1-7.

U.S. Centers for Disease Control and Prevention (CDC). "Increase in Coccidioidomycosis - United California, 2009." Mortality and Morbidity Weekly Report (MMWR). February 13, 2009: 58(5):105-109.

Pronunciation: kok-si-dee-oh-my-KOH-sis

Also Known As:

  • Coccidioidal Granuloma
  • Cocci
  • "California Fever"
  • "Desert Rheumatism"
  • Posadas Wernicke Disease
  • "San Joaquin Valley Fever"

Common Misspellings: coccidiomycosis