Definition of Valley Fever

Valley fever: A disease also called coccidioidomycosis (CM) due to a fungus called Coccidioides immitis. About 40% of people infected with this fungus develop symptoms. Most often they have an influenza-like illness with fever, cough, headaches, rash, and myalgias (muscle pains). Of those people with symptoms, 8% have severe lung disease requiring hospitalization and 7% develop disseminated infection (throughout the body).

Groups at high risk from the fungus include African-Americans and Asians, pregnant women in the third trimester, smokers, the elderly, diabetics and people with an impaired immune system. Severe disease tends particularly to strike in HIV-infected persons. The mortality is high in HIV-infected persons with diffuse lung disease. CM meningitis can lead to permanent brain damage.

The fungus is in the soil in semiarid areas (primarily in the "lower Sonoran life zone"). The disease is endemic (constantly present) in the southwestern US and parts of Mexico and South America. Inhalation of airborne spores after disturbance of soil by people or natural disasters (such as wind storms and earthquakes) exposes people (as for example, construction or agricultural workers and archeologists) to the dust containing the spores. A mask helps but does not provide complete protection against the fungus.

The incidence of the disease was 15/100,000 in Arizona in 1995. Of persons living in areas with endemic disease, between 10% and 50% have been found to show a positive skin test to CM. In one outbreak, 35 church members from Pennsylvania traveled to Hermosillo, Mexico, where they stayed a week to build a church. Within 2 weeks of returning home, 27 of the travelers complained of flu-like symptoms and testing revealed exposure to the fungus that causes CM.

The disease is also known by a number of other names including desert fever, Posadas disease, San Joaquin fever, San Joaquin Valley disease, and San Joaquin Valley fever.