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Prevalence of Valley Fever increasing substantially


Valley Fever, a fungal respiratory infection, dramatically increased in several southwestern states from 1998 to 2011, according to a study by the Centers for Disease Control and Prevention.

Annual cases in Arizona, California, Nevada, New Mexico and Utah rose from 2,265 to more than 22,000 during that span, according to the report.

Valley Fever — clinically known as Coccidioidomycosis — is caused by inhaling the fungus Coccidioides, which lives in the soil in the southwestern United States. Not everyone who is exposed to the fungus gets sick, but those who do typically have flu-like symptoms that can last for weeks or months. More than 40% of patients who get ill from Valley Fever may require hospitalization at some point, with an average cost of nearly $50,000 per hospital visit. Previous studies have shown that of those who get sick, nearly 75% miss work or school for approximately two weeks.

“Valley Fever is causing real health problems for many people living in the southwestern United States,” CDC Director Tom Frieden, MD, MPH, said in a news release. “Because fungus particles spread through the air, it’s nearly impossible to completely avoid exposure to this fungus in these hardest-hit states. It’s important that people be aware of Valley Fever if they live in or have traveled to the southwest United States.”

The recent increase in Valley Fever could be related to several factors, including: changes in weather, which could affect where the fungus grows and how much of it is circulating; higher numbers of new residents; or changes in the way the disease is detected and reported to the states or CDC. More research is needed to understand why the number of reported cases of Valley Fever has increased, the researchers said. Between 1998 and 2011, Arizona and California had average increases in Valley Fever incidence of 16% and 13% per year, respectively. The CDC has provided grants to these two states to study the disease.

During the time period studied, nearly 112,000 cases of Valley Fever were reported from 28 states and Washington, D.C., with about 66% of cases in Arizona, 31% in California, 1% combined in Nevada, New Mexico and Utah, and about 1% combined in all other states.

“It’s difficult to say what’s causing the increase,” Benjamin J. Park, MD, chief epidemiologist with the CDC’s Mycotic Diseases Branch, said in the news release. “This is a serious and costly disease and more research is needed on how to reduce its effects.”

Clinicians and patients should know that the symptoms of Valley Fever are very similar to flu or pneumonia symptoms, and a lab test is the only way to determine whether an illness is Valley Fever. Not everyone who gets Valley Fever needs treatment, but for people at risk of the more severe forms of the disease, early diagnosis and treatment is important, the CDC stated. The best way to treat Valley Fever still needs to be studied, especially with the number of cases continuing to rise.

The study released Thursday was based on reporting of Valley Fever to the National Notifiable Disease Surveillance System. Many states collect and report case counts to the CDC through this surveillance system.

The study was published in the March 29 issue of the Morbidity and Mortality Weekly Report, and is available at


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