In California and Arizona (USA), a little-known fungal disease, coccidioidomycosis, is increasingly affecting local communities and vulnerable populations. Incidence of the disease in California rose 42% from 2016 to 2017 and then an additional 10% from 2017 to 2018. A similar trend has been observed in Arizona, where incidence increased 36% from 2008 to 2017 (73 cases per 100,000 to 99 cases). Additionally, the disease appears to disproportionately affect certain races/ethnicities, but these associations are not well characterized. Many are not aware of the “silent epidemic” of Valley fever due in part to the limited geographic range of the disease and relatively low national incidence compared to higher-profile diseases. For those who live in endemic areas and are in a high-risk population, however, the disease is quite a serious threat.

In this week’s Outbreak Thursday, we will take a closer look at this emerging infection and efforts to better understand this disease and its health impacts.

What is coccidioidomycosis?

Coccidioidomycosis (pronounced kok-sid-ee-oy-doh-my-KOH-sis), also commonly referred to as Valley fever, is a fungal disease typically transmitted by inhalation of Coccidioides spores, although rare instances of transmission via spores entering wounds in the skin, fomites, and contaminated organ donation have been documented as well. These spores reside in dust and soil in parts of the United States as well as Mexico, Central America, and South America. States with endemic spores include Arizona, California, Nevada, New Mexico, Texas, Utah, and Washington. California and Arizona typically account for the overwhelming majority of Valley fever cases in the US. In 2017, a total of 14,364 cases of Valley fever were reported nationwide—13,810 of which were in Arizona and California.

Symptoms typically present within 1-3 weeks of exposure and include fatigue, cough, difficulty breathing, headache, night sweats, muscle aches or pains, and rash. At this stage of disease, symptoms can last for months but typically resolve without treatment. Approximately 5-10% of Valley fever cases develop severe or chronic pulmonary issues, and about 1% of cases develop disseminated disease, which can affect bones and joints, soft tissues, and meninges. Morbidity for the disease is relatively severe, particularly from a financial perspective, due to limited and costly treatment options. Nearly 75% of symptomatic cases result in missed work or school, with an average of three weeks missed. Additionally, approximately 40% of cases are hospitalized, at an average cost of $50,000.

Risk Factors & Vulnerable Populations

Populations living in endemic areas are at risk for the disease, but certain activities such as those that involve close contact with dirt or dust, increase the risk. Individuals such as farmers, military servicemembers, and construction workers as well as individuals who live near areas where dirt or soil are disturbed may be at an elevated risk of infection. Additionally, certain populations are at a greater risk of developing severe disease including individuals over the age of 60, pregnant women, individuals with compromised immune systems, and those with other comorbidities (eg, diabetes). Additionally, individuals of African, Hispanic, or Filipino ancestry have been found to be at elevated risk of severe disease; however, the link between race/ethnicity and Valley fever severity is not fully understood, and a number of confounding factors, including large populations of Hispanics living and working in endemic regions as well as diagnosis and reporting challenges, could be contributing to the identified association.

Over the past several years, a number of lawsuits have been filed by prisoners who were housed at correctional facilities in California over concerns that the state was negligent in efforts to prevent or control Valley fever in inmates. A study of Valley fever incidence among California prison inmates in 2011 actually resulted in a US district court ordering the state of California to remove all African American inmates and inmates with diabetes from two Southern California facilities responsible for more than 80% of the state’s Valley fever cases among inmates. Recently, the 9th Circuit Court of Appeals dismissed a lawsuit that aimed to hold state officials responsible for not acting sooner. The health of prisoners was under the purview of federal authorities, and a judge indicated that it was not reasonable for the state to expect the need to segregate prisoners by race.

Preventing Valley Fever

Risk and severity of infection can be mitigated by implementing practices that reduce exposure to dust or limit or prevent soil disturbance. Individuals who live in endemic areas should stay inside during dust storms and keep doors and windows tightly closed. For those who work in high-risk occupations, the Occupational Health and Safety Administration (OSHA) requires employers to control workers’ exposure to all job hazards, including Coccidioides. For example, wetting soil prior to digging can reduce dust and spore inhalation, and above-ground work should be favored over below-ground work whenever possible. If it is not possible to prevent airborne dust, staying upwind of digging or excavation and wearing N-95 respirators can limit or prevent inhalation of contaminated dust.

Raising Awareness for a Growing Threat

According to the Valley Fever Institute, part of the Kern Medical teaching hospital (affiliated with the University of California Los Angeles), as many as 60% of cases are misdiagnosed as influenza and go untreated. In the Phoenix and Tucson metropolitan areas of Arizona, Valley fever may be responsible for 15-30% of community-acquired pneumonia cases; however, low awareness and lack of testing for the disease by healthcare providers can lead to underreporting as well as misdiagnosis and delayed or improper treatment. Increased awareness of the disease among healthcare providers can facilitate rapid and accurate diagnosis, which could improve reporting and ideally mitigate severe disease in some individuals.

The root cause of the recent increase in Valley fever incidence is not fully understood, but hypotheses include improved reporting mechanisms, climate change leading to weather events that disrupt soil, increased soil disturbance due to construction, and increasing numbers of at risk or susceptible persons living in endemic areas.

Among the US CDC’s research priorities for Valley fever are:

  • Identifying host factors associated with increased risk for dissemination in select racial/ethnic groups to target prevention efforts

  • Understanding the factors associated with increasing incidence in endemic areas

  • Determining the influence of climate change on Coccidioides’ geographic distribution

These priorities highlight the need to better characterize the epidemiology of this disease, particularly in high-risk, vulnerable populations. Additionally, the interest in the geographic scope of the disease and the potential impacts of climate change signal the possibility that the risk could begin to extend beyond current endemic regions.

Recently, a bipartisan group of Senators and Representatives from California and Arizona introduced bills to the US Senate and House of Representatives, dubbed the “Finding Orphan-disease Remedies With Antifungal Research and Development [FORWARD] Act of 2019,” targeted at tackling Valley fever by increasing public awareness and promoting the development of a vaccine and novel treatments. Similar bills have been introduced in the past but have not resulted in national legislation.


Valley fever is a growing health threat, and the burden of disease, potential link to certain races/ethnicities, and prospect of expanding geographic range make it all that more important to educate health professionals, elected officials, and the public and enact policies to protect vulnerable populations. Continued efforts are required to better characterize the disease epidemiology, improve diagnosis and reporting, and develop improved medical countermeasures to stem the growing trend observed in recent years.

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.

Photo courtesy of CDC Public Health Image library (