Risk factors for Valley fever among Hispanic California farmworkers


Farmworkers who pick root crops, such as beets and carrots, and those who perform tasks that increase dust exposure might have a higher risk of contracting Valley fever. That was a key research finding discussed by Stephen McCurdy, professor emeritus at the UC Davis Departments of Public Health Sciences and Internal Medicine, during a Dec. 7 seminar about the deadly fungal infection.

Farm workers are at higher risk for Valley fever. <em>Hector Amezcua, College of Agricultural and Environmental Sciences, UC Davis</em>
Farm workers are at higher risk for Valley fever. Hector Amezcua, College of Agricultural and Environmental Sciences, UC Davis

The event, organized by the Western Center for Agricultural Health and Safety (WCAHS), highlighted the risks of certain agricultural practices and crops for Valley fever among Hispanic California farmworkers.

What is Valley fever?

Valley fever (coccidioidomycosis) is an infection caused by the inhalation of Coccidioides spores living in the soil. Dust storms, earthquakes, wind and activities that disturb the soil can release the fungus spores into the air. In the U.S., the fungus can be found in dry, hot regions across the southwestern region.

Around 97% of cases in the U.S. are in California and Arizona. In recent decades, Valley fever infections have surged, especially in California.

In 2019, there were more than 9000 cases in California, the highest in the last 25 years. In the San Joaquin Valley, Kern County, the most productive agricultural county in the nation, is home to the greatest number of Valley fever cases in California. Soil disruption and exposure to agricultural dust in this region are common.

Around 40% of Valley fever infections cause flu-like symptoms, such as cough, fever and fatigue and typically resolve without treatment. Less than 5% of cases involve fungal spread to the skin, bone and other tissues. The more severe cases typically need long-term antifungal therapy and have a higher risk of death.

Is the risk to Valley fever linked to the type of crop or specific agricultural tasks?

McCurdy, who is the former director of WCAHS outreach, presented the findings from his recently published study in the Journal of Emerging Infectious Diseases and other on-going projects.

“We had a gap in our knowledge of the people’s awareness, attitudes, beliefs and behaviors related to Valley fever,” McCurdy said. “We also wanted to identify specific tasks or crops in agricultural work that could put farmworkers at increased risk of Valley fever.”

McCurdy and his colleagues found that around 75% of the surveyed Hispanic workers living in two migrant housing centers in Kern County were aware of Valley fever infection, its basic features and the role of dust exposure. However, they had misconceptions about pesticides and the effectiveness of a cloth bandana as a protective cover.

In another study, McCurdy and his team used a case-control design, comparing a group of 110 farmworkers with the disease to a control group of 93 without it. The researchers partnered with the Kern County Public Health Services Department to recruit agricultural workers to engage in an interview, undergo antibody blood testing, and report clinical symptoms. They analyzed the responses by crop category and by task to identify any associations with the clinical characteristics of the disease.

Exposure to dust and working with root and bulb crops were associated with an increase in the odds of contracting Valley fever.

Results from the study confirm that exposure to dust nearly doubled the risk of getting the disease. They found that practices like wearing face coverings and bandanas or wetting the soil in dusty conditions resulted in a modest (statistically insignificant) reduction of infection risk.

The risk was nearly threefold for those who worked with root and bulb vegetable crops, such as beets, carrots, garlic, onions, radishes and sweet potatoes. People who worked with leaf removal (primarily used in grape cultivation) had a 60% reduction in their odds of getting the disease. This is possibly related to reduced direct contact with dust and dirt.

The study found that cloth bandanas offer limited respiratory protection. The use of NIOSH-approved personal respiratory protection is recommended.

Analysis of clinical symptoms showed that the disease carries a significant health burden. Around 80% of those who had Valley fever reported fatigue or weakness and an associated loss of workdays. The study documented a median of 18.5 lost workdays, approximately 10 percent of the average annual workdays of California farmworkers. This missed work represents a significant loss of income for workers and loss of productivity for farms.

Further research and targeted health education on Valley fever

McCurdy recommended additional research on exposure. This includes soil and air sampling during harvest and other phases of cultivation, especially for root and bulb vegetable crops.

“Because the farmworker population faces linguistic and cultural barriers to awareness of health risks, we encourage educational campaigns on Valley fever targeting these demographics,” McCurdy said.

This article was written in collaboration with the UC Davis Center for Valley Fever.

Valley Fever Resources:

Video of Prof. Stephen McCurdy’s WCAHS seminar on Valley fever

Kern County Public Health Services Valley Fever Website

California Department of Public Health Valley Fever Information

WCAHS Valley Fever Research