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Risk of infection is highest in dry summer months. The arid areas of the Sonora Desert in Arizona, including Phoenix and Tucson, and the San Joaquin Valley and Central Coast of California report the highest incidence. New Mexico, western Texas, Nevada and Utah are also endemic.
Valley Fever, also known as Coccidioidomycosis, is caused by inhaling the fungal spores Coccidioides immitis and Coccidioides posadasii found in dust and soil particles in arid areas.
The fungal spores responsible for Valley Fever are present in arid regions of the USA, Central America, and South America. Travellers undertaking outdoor activities such as camping, mountain biking, and motocross are at risk. Valley Fever is an occupational hazard for archaeologists, farmers, and miners whose activities disturb the ground and generate dust clouds. Windstorms and earthquakes can also spread the fungus.
In the majority of cases, the infection is asymptomatic – persons do not exhibit symptoms. Those who get ill typically present with flu-like symptoms 7 to 21 days after inhaling the fungal spores, including fever, headache, muscle pain, dry cough, weight loss, rash, and pneumonia. In rare cases, the illness may progress to lung disease and affect the central nervous system, as well as the joints, bones and skin. Older persons and those pre-existing health conditions such as diabetes are more susceptible to developing the illness. Once infected, a person is immune to the disease. Treatment may include antifungal therapy.
Travellers should limit exposure to outdoor dust and take dust-control measures. There is no preventive medication or vaccine against Valley Fever.
Information last updated: February 23, 2021.