Coccidioidomycosis (also known as desert fever, San Joaquin Valley fever, Valley fever, and desert rheumatism) is a deep fungal infection caused by the dimorphic fungi Coccidioides immitis and Coccidioides posadasii, acquired via the respiratory route.

Coccidioidomycosis is endemic in the southwestern United States (with many cases in Arizona, the San Joaquin Valley in California, New Mexico, and western Texas), with sporadic cases in places where the disease is not endemic (some cases may be due to reactivation of infection acquired in an endemic area). Cases of symptomatic coccidioidomycosis are on the rise, and the geographic range of endemicity appears to be expanding.

Overall, rates are higher among individuals aged 60 years and older. In 2019, about 20 000 cases were reported in the United States. However, data models estimate actual annual US cases to be 10-18 times higher (206 000-360 000) than nationally reported (due to patients not seeking medical care or being undiagnosed or misdiagnosed), with 18 000 to 28 000 related hospitalizations and 700 to 1100 deaths. In 2021, Texas had 709 hospitalized cases; however, coccidioidomycosis is not a reportable disease in Texas, indicating that the true number of infections is likely higher. In 2023, both Arizona and California broke past records, reporting 19 845 and 9280 cases of coccidioidomycosis respectively.

Much of this expansion of endemic range is felt to be related to climate change, and studies predict expansion of the endemic range of coccidioidomycosis to the east of the Mississippi River and north as far as North Dakota by 2065.

Approximately one-half to two-thirds of infected individuals are asymptomatic. The remaining infected individuals develop an acute or subacute community-acquired pneumonia 1-3 weeks after exposure. The clinical presentation includes dry cough, pleuritic chest pain, myalgia, arthralgia, fever, sweats, anorexia, and weakness. An exanthematous eruption, erythema multiforme, and/or erythema nodosum may accompany primary pulmonary infection. Infection is typically self-limited, lasting weeks, and can resolve without therapy. The illness is often indistinguishable from common bacterial or viral pneumonias, although marked fatigue may persist for weeks to months following illness. As a consequence of infection, 5%-10% of patients may develop pulmonary nodules.

Of those symptomatic patients, 1 in 200 will develop extrapulmonary disease that can spread via hematogenous dissemination to subcutaneous tissues, bone, skin, and meninges. Disease dissemination appears to be more common in Black individuals and individuals of Filipino ancestry than in White individuals but is markedly higher in the immunocompromised host (30%-50% chance of dissemination). Disseminated disease may run a remittent or fulminant course and progress to miliary lung granulomas, meningitis, and hydrocephalus. The mortality rate is greater than 90% after 1 year without therapy. Meningitis requires lifelong therapy to prevent relapse and associated morbidity / mortality.

Primary inoculation coccidioidomycosis is rare and is generally self-limited but may rarely be complicated by meningitis or miliary lung granulomas.

Pregnant individuals may be at increased risk of severe illness from coccidioidomycosis. Coccidioidomycosis acquired during the latter half of pregnancy is more likely to disseminate.