A family member tends to her husband, who is suffering from Valley Fever and other medical problems, in their apartment in Madera, Calif. Valley Fever, a little-known disease infecting more people nationwide every year, is especially prevalent in California’s San Joaquin Valley. Every day millions of residents in this agricultural region live with the threat of the disease, which is caused by a fungus in the soil. People who work in dusty fields or construction sites are most at risk, but even visitors passing through the valley can contract Valley Fever. (AP Photo/The Fresno Bee, John Walker)
Copyright 2008 AP. All rights reserved.
Cases of Valley Fever, a potentially deadly fungal infection that is spread in contaminated soil, are already on track to top the past several years’ record-breaking numbers.
There were 6,761 confirmed cases by the end of July, which means if this pace continues, the total numbers for this year will likely exceed the 12,595 cases reported in 2024. This increase has prompted renewed public health warnings and highlights the urgent need for greater awareness of this potentially serious fungal infection.
What Causes Valley Fever and How Is It Transmitted?
Coccidioidomycosis, commonly known as Valley Fever, is caused by the fungus Coccidioides, which exists naturally in the soil of certain arid and semi-arid regions. The fungus thrives in areas with hot, dry summers and mild winters, making California, Arizona and parts of Nevada, New Mexico, northern Mexico and South America prime endemic zones.
Illustration of thick-walled arthroconidia and arthrospores from the fungus Coccidioides immitis. This fungus is found in desert and semi-arid regions and is endemic to south-western U.S., Mexico and South America. Coccidioides is the causative agent of coccidioidomycosis, also known as valley fever. The route of infection is almost always pulmonary, by inhalation of the spores. Agricultural workers are particularly at risk. Symptoms include a cough, chest pain, fever, rash and fatigue.
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The disease is transmitted through inhalation of fungal spores called arthroconidia. When soil containing the fungus is disturbed by activities such as construction, farming, excavation or strong winds, the microscopic spores become airborne and can travel significant distances. People become infected by breathing in dust particles that are contaminated with the microscopic spores.
Importantly, Valley Fever is not contagious between people or animals, meaning that an infected person can’t transmit the disease to another individual or pet. The infection comes from environmental exposure to contaminated soil.
Weather patterns and climate change have significantly impacted the risk of transmission. Periods of increased rainfall followed by dry conditions create an ideal setting for fungi to grow and disperse spores. This explains why California has seen such an increase in cases following recent wet winters, as the enhanced fungal growth eventually leads to greater spore production when conditions dry out. In addition, the rise in construction along with an increased rate of wildfires may contribute to increased transmission of this fungal pathogen.
Often Silent, Yet Potentially Deadly
Fortunately, nearly 60% of those infected with Coccidioides will not develop symptoms. However, in the remaining 40%, symptoms typically appear one to three weeks after exposure, though they can emerge anywhere from a few days to several months later. The disease presents in various forms, ranging from mild to severe.
Most people with Valley Fever experience flu-like symptoms that can persist for weeks to months. Symptoms can include persistent fatigue, fever, dry cough, chest pain, shortness of breath, headaches, muscle aches and joint pain. Many patients also develop a characteristic skin rash with red bumps or patches. The fatigue associated with Valley Fever can be particularly debilitating and may last for months even after other symptoms resolve.
In approximately 5-10% of cases, the infection may progress to a chronic pulmonary form, causing persistent pneumonia-like symptoms, with the development of lung nodules that may be seen on chest X-ray. Less commonly, the infection can spread beyond the lungs to other parts of the body, including bones, joints, skin and the central nervous system. This disseminated form is more serious and has a higher prevalence in pregnant women, people with a compromised immune system and certain ethnic groups including African Americans, Filipinos and Hispanics.
Testing and Diagnosis
Diagnosing Valley Fever can be challenging because its symptoms may closely resemble other respiratory illnesses. Many cases go undiagnosed or are misdiagnosed, leading healthcare providers to prescribe unnecessary antibiotics instead of antifungal medication.
Several testing methods are available for diagnosis. Blood (i.e., serology) tests can detect antibodies that the immune system produces in response to the fungal infection. The fungus can also be grown in culture, but this can take several days, which may delay diagnosis and treatment. Molecular, or PCR, tests are available at select laboratories and can provide a rapid diagnosis from samples such as sputum, tissue or cerebrospinal fluid.
Healthcare providers should consider Valley Fever testing for patients in endemic areas who present with persistent respiratory symptoms, especially during peak transmission seasons, which are usually late fall and early winter.
Prevention Strategies
Workers wear protective face masks for safety.
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While it’s impossible to completely eliminate the risk of Valley Fever in endemic areas, there are several measures people can take to significantly reduce the risk of becoming infected.
The most effective prevention involves minimizing exposure to dust and disturbed soil. During high-risk periods, particularly windy days or dust storms, people should stay indoors with windows and doors closed and use air purification systems with high-efficiency filters. When outdoor activities are necessary, wearing a mask can protect against inhaling fungal spores. Those working in high-risk occupations, such as construction or agriculture, should use appropriate respiratory protection.
Individuals at higher risk for severe disease, including pregnant women or those with a compromised immune system, should take extra precautions. This may include avoiding high-risk activities entirely and consulting with their healthcare providers about steps to stay safe and symptoms to watch out for.
As Valley Fever cases continue to climb in California and other southwestern states, awareness and prevention become increasingly important. Understanding this fungal disease, recognizing its symptoms and taking appropriate protective measures can help individuals and communities better navigate this growing public health challenge.
