Increased risk of Valley fever linked to fine mineral dust exposure

A new study led by researchers at UC Berkeley School of Public Health found a link between exposure to fine mineral dust and an increased risk of Valley fever, an emerging infectious disease that is becoming increasingly common in California and other southwestern states. The research, appearing in the journal Environmental Health Perspectives published by the National Institute of Environmental Health Sciences, found that census tracts with higher concentrations of fine mineral dust had higher incidence rates of Valley fever.

Valley fever (also called coccidioidomycosis) is an infectious disease caused by inhaling spores of the fungus Coccidioides immitis. The fungus is found in the soil in arid regions of the southwestern United States, and it can be stirred up into the air along with dust by wind, construction, or other activities. The disease is on the rise in the southwestern United States, including California—which has seen record incidence in recent years, including an outbreak of cases possibly associated with an outdoor music festival near Bakersfield in 2024. Symptoms of Valley fever can include fever, cough, chest pain, fatigue, and skin rash. In some cases, the infection can be serious and even life-threatening.

“Our research brings attention to the role of dust exposures in the spread of this emerging infectious disease,” says Dr. Amanda Weaver, who led the research and recently completed her PhD in the division of Environmental Health Sciences. The researchers analyzed thousands of cases of Valley fever in California over an 18-year period, applying statistical models to examine the relationship between mineral dust concentrations and coccidioidomycosis incidence across the San Joaquin Valley. They found that the risk of Valley fever increased with increasing levels of fine mineral dust exposure, particularly when dust exposures occurred during dry, hot periods, or after a wet winter.

“Our findings suggest that exposure to fine mineral dust at specific times and locations may pose greater risk than others for Valley fever,” said Weaver. “This is important because it could help us to identify where and when limiting dust exposure would provide the most protection. We can also use this information to encourage people with symptoms to talk to their health care providers about dust exposures and to specifically mention Valley fever.”

This study is the first to use new, advanced air pollution data to specifically analyze the Valley fever risks associated with fine mineral dust, the component of particulate matter that directly originates from soils and is likely to co-occur with the Coccidioides fungus. Previous research has relied on rough approximations, such as measures of particulate matter from all sources, which includes many non-mineral components.

The research has important implications for public health policy, particularly in areas with high levels of dust where Coccidioides readily grows. “By understanding the link between dust exposure and Valley fever, public health officials can better target interventions, such as dust control measures and campaigns to increase public awareness of the risks associated with dust exposure, particularly among outdoor workers and those new to areas where Valley fever is prevalent,” said Justin Remais, professor and chair of Environmental Health Sciences at UC Berkeley School of Public Health and principal investigator of the research project. “We should take extra precautions to educate the public, employers, and health care providers about the unique risks of exposure to mineral dust during the summer and fall,” he added.

The results are particularly important in light of the potential effects of climate change on the spread of Valley fever. Droughts, which are expected to become more frequent and severe with climate change, can lead to increased dust emissions, putting more people at risk of Valley fever in the future. “We need to be prepared for the possibility of continued increases in Valley fever incidence in the future, and we need information on where and when those increases are most likely,” said Remais.