Coccidioidomycosis / Valley Fever

CDC Yellow Book 2024

Travel-Associated Infections & Diseases

Author(s): Mitsuru Toda, Kaitlin Benedict, Tom Chiller

INFECTIOUS AGENT: Coccidioides immitis and C. posadasii


The Americas (Central and South America, northern Mexico, and the United States, specifically Arizona and Southern California)


Adventure tourists
Humanitarian aid workers
Long-term travelers and expatriates
Study abroad students
Travelers visiting friends and relatives


Limit exposure to outdoor dust in endemic areas
Use personal protective equipment (e.g., N95 respirator) when working outdoors in endemic areas
Preventive antifungal medication


A clinical laboratory certified in moderate complexity testing; or contact CDC’s Mycotic Diseases Branch Reference Laboratory Team (404-639-2569)

Infectious Agent

Valley fever (coccidioidomycosis) is caused by the fungi Coccidioides immitis and C. posadasii.


Transmission occurs through inhalation of fungal conidia from the environment. Transmission from person to person does not occur.


Coccidioides is endemic to the western United States, particularly Arizona and Southern California, and parts of Mexico and Central and South America. Travelers, including adventure tourists, expatriates, humanitarian aid workers, long-term travelers, and travelers visiting friends and relatives (VFRs) are at increased risk if they participate in activities that expose them to soil disruption and outdoor dust. Participating in activities like community house-building projects, gardening, four-wheeling, and horseback riding can put people at risk. Coccidioidomycosis outbreaks have been associated with activities such as archaeological excavation, construction, and military training exercises.

Clinical Presentation

The incubation period is 7–21 days. About 40% of infected people develop symptomatic infections, ranging from primary pulmonary illness to severe disseminated disease. The most common symptoms of primary pulmonary coccidioidomycosis are cough and persistent fatigue, with only about half of patients reporting fever. Other symptoms include shortness of breath, headache, joint pain, muscle aches, night sweats, and rash. Symptoms can be indistinguishable from bacterial pneumonia. Coccidioidomycosis infections are often self-limited, typically resolving in a few weeks to months, but also can be severe, requiring hospitalization. An estimated 5%–10% of people develop serious or chronic lung disease (e.g., bronchiectasis, cavitary pneumonia, pulmonary fibrosis). About 1% of illnesses result in meningitis, which can require lifelong antifungal therapy; dissemination to bones, joints, and skin also can occur.

People ≥65 years of age, people with diabetes, people who smoke, and people with high inoculum exposure are at increased risk of developing severe pulmonary complications. Those with depressed cellular immune function (e.g., people with HIV, organ transplant recipients) and people who are pregnant are at increased risk for developing disseminated disease. Epidemiological data suggest that the risk for severe illness is increased among people of African American, Filipino, and Pacific Island descent, but further study is needed to understand the reasons for this association.


Coccidioidomycosis is a nationally notifiable disease in the United States. The most common methods to diagnose coccidioidomycosis are culture, histopathology, molecular techniques, and serology. Isolation of Coccidioides from fungal culture of respiratory specimens or tissue provides a definitive diagnosis. Microscopy of sputum or tissue can identify Coccidioides spherules but has low sensitivity. Molecular techniques include DNA probe for confirmation of cultures, as well as PCR for direct detection from clinical specimens, which became commercially available in early 2018. EIA is a sensitive serologic method to detect IgM and IgG antibodies. Immunodiffusion and complement fixation can also detect antibodies and are often used to confirm diagnosis. Lateral flow assays to detect any antibodies in serum became commercially available in 2018.


Expert opinions differ on the proper management of patients with uncomplicated primary pulmonary disease in the absence of risk factors for severe or disseminated disease. Some experts recommend no therapy, since most illnesses are self-limited, whereas others advise treatment to reduce the intensity or duration of symptoms. Treatment with antifungal agents has not been proven to prevent dissemination. People at high risk for dissemination should receive antifungal therapy, as should people with clinical manifestations of severe acute pulmonary disease, chronic pulmonary disease, or disseminated disease. Depending on the clinical situation, a variety of antifungal agents can be used, including amphotericin B and fluconazole (or itraconazole).


To reduce risk for coccidioidomycosis, travelers should limit exposure to outdoor dust in endemic areas, or wear an N95 respirator if they cannot avoid dusty areas while in this environment. During dust storms, travelers should stay inside and close windows. Travelers to known endemic areas also should avoid activities that require close contact with dirt or dust, including digging, gardening, and yard work. Air filtration measures can be used indoors. Preventive antifungal medication (fluconazole or itraconazole) can be taken in certain circumstances if recommended by a health care provider.

CDC websites:

The following authors contributed to the previous version of this chapter: Orion Z. McCotter, Tom M. Chiller

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Freedman M, Jackson BR, McCotter O, Benedict K. Coccidioidomycosis outbreaks, United States and worldwide, 1940–2015. Emerg Infect Dis. 2018;24(3):417–23.

Rosenstein NE, Emery KW, Werner SB, Kao A, Johnson R, Rogers D, et al. Risk factors for severe pulmonary and disseminated coccidioidomycosis: Kern County, California, 1995–1996. Clin Infect Dis. 2001;32(5):708–15.

Toda M, Gonzalez FJ, Fonseca-Ford M, Franklin F, Huntington-Frazier M, Gutelius B, et al. Notes from the field: multistate coccidioidomycosis outbreak in U.S. residents returning from community service trips to Baja California, Mexico—July–August 2018. MMWR Morb Mortal Wkly Rep 2019;68(14):332–3.