Valley Fever, or Coccidioidomycosis, is a respiratory infection caused by a fungus that lives in the soil of specific arid regions. The disease is highly concentrated in the southwestern United States, with Arizona reporting a disproportionately large number of cases each year. Understanding where the fungus is most prevalent is a practical step for residents and visitors to manage their exposure risk. The geographical patterns of infection relate directly to the environmental conditions necessary for the fungus to thrive and release its infectious spores into the air.
Understanding Valley Fever
The infection is caused by two species of the Coccidioides fungus found in desert soil. This fungus exists as mold, forming thread-like structures that produce tiny, infectious spores. The spores are extremely lightweight and become airborne easily when the soil is disturbed by wind, construction, or other activities.
Infection occurs when a person inhales these airborne spores into their lungs. Once inside the lungs, the spores morph into larger, spherical structures called spherules, which reproduce and cause disease. The infection is not contagious from person-to-person or animal-to-person, as exposure is tied directly to the land.
Mapping the Risk: Geographical Distribution in Arizona
Arizona is the most highly endemic state for Valley Fever in the United States, accounting for approximately two-thirds of all cases reported nationally. The fungus requires arid or semi-arid climates, hot summers, mild winters, and alkaline soil conditions. These factors are primarily concentrated in the southern, lower-elevation portions of the state.
The majority of Arizona’s reported cases originate from three major counties: Maricopa, Pima, and Pinal. Maricopa County (Phoenix area) reports the highest raw number of cases due to its large population living on top of a fungal reservoir. Pima County (Tucson) and Pinal County also exhibit some of the nation’s highest incidence rates per capita.
The risk of spore dispersal increases following periods of heavy winter and spring rainfall, which encourages fungal growth, followed by hot, dry conditions. When the soil dries out, the fungal structures break apart. Activities like farming, earth-moving construction projects, and severe dust storms increase the concentration of infectious spores in the air.
Recognizing Infection: Symptoms and Diagnosis
The body’s reaction to inhaling the spores varies widely, as an estimated 60% of infected individuals remain asymptomatic. For those who develop symptoms, they typically appear one to three weeks after exposure and often mimic the common flu.
Symptoms include persistent fatigue, fever, cough, night sweats, and joint aches. Some individuals may also develop a rash. In a small percentage of cases, the infection can progress to chronic pneumonia or, rarely, disseminate, spreading from the lungs to other body parts like the skin, bones, or central nervous system.
Diagnosis relies heavily on a patient’s geographic history, so informing a healthcare provider about residency or recent travel to endemic areas is important. Doctors confirm the infection using blood tests that look for antibodies the body produces in response to the fungus. Early diagnosis is particularly important in severe cases that require antifungal treatment.
Reducing Exposure in Endemic Areas
Individuals can take practical steps to reduce their exposure in high-risk areas like central and southern Arizona. During activities that disturb the soil, wetting the ground beforehand helps keep dust and spores from becoming airborne. Wearing an N95 respirator mask offers protection when working directly with disturbed soil.
Residents can minimize interior exposure by keeping windows closed during high-wind events and dust storms. For workers in high-risk occupations like construction or agriculture, using enclosed cabs with high-efficiency particulate air (HEPA) filtration systems is a protective measure. Changing clothes after working in dusty environments can also limit the amount of fungal spores brought indoors.