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As CA droughts rise, Valley fever cases increase, UC Berkeley study finds

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Valley fever is contracted when people inhale dust; symptoms include coughing, difficulty breathing and joint stiffness. One to 5% of infected individuals can progress to a chronic infection and have recurring symptoms throughout their lifetime. Photo by Bernt Rostad under CC BY 2.0


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OCTOBER 10, 2022

A study conducted by UC Berkeley researchers in collaboration with the California Department of Public Health found a connection between droughts and increases in coccidioidomycosis, or Valley fever, cases.

Specifically, having wet seasons followed by droughts allows the fungus that causes Valley fever to flourish and spread to people who live in drought-ridden areas.

“We first started looking at the relationship between various meteorological factors like rainfall and temperature and incidents. There we found that rainfall in the winter helped promote incidents of coccidioidomycosis or Valley fever in the fall,” said Jennifer Head, a campus assistant researcher in the division of environmental sciences in the school of public health. “We think this is because fungi need moisture to grow and since California receives most of its rainfall during the winter that’s the period of time where much of the growth of this fungus could be happening in the soil.”

According to Head, Valley fever is a fungal pathogen that lives in soil. Their team has hypothesized that the increase in Valley fever cases is due to the spores of the fungus surviving through seasons of drought while its competitors die off. When rain comes to the region, the spores are able to flourish within the soil.

It is contracted when people inhale dust, Head said, in a region where the coccidioides spores are growing.

“The spores can become airborne through direct disturbance of the soil, so things like digging in the soil or doing construction can cause illness,” Head said. “If it’s a windy day and the soil is being carried into the air, the spores can also be picked up and inhaled by humans.”

Symptoms of Valley fever include coughing, difficulty breathing and joint stiffness, Head noted. However, approximately 60% of people who contract this disease do not experience symptoms.

For the other 40% of people who contract the virus, the median duration of symptoms is 42 days, Head added. One to 5% of infected individuals can progress to a chronic infection and have recurring symptoms throughout their lifetime.

“The best prevention is just awareness — making the public aware of what the symptoms of Valley fever are so that if they’re experiencing a cough they can go seek healthcare and hopefully get diagnosed,” Head said.

Head added that there will likely be a spike in Valley fever cases after the current drought in California is over. In addition, this research has implications for fungal viruses in other drought-plagued regions, including Arizona, Texas, Nevada and Utah, which are expected to see increases in Valley fever in the future.

Contact Zoe Kessler at 


OCTOBER 10, 2022