August 11, 2017
2 min read

No explanation for record number of California valley fever cases

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State and federal health investigators are still unsure of the reasons behind last year’s record number of valley fever cases in California but said the spike may have been caused by changes in climate and the environment.

They urged health care providers to be on the lookout for the condition, which is spread through airborne dust, in patients who have lived in or traveled to endemic areas.

The condition — also known as coccidioidomycosis — is caused by a fungus called Coccidioides that is found in soil in the southwestern United States and parts of Central and South America. Most people who breathe in the fungal spores are not affected, but some can become ill with influenza-like symptoms or, in rarer cases, develop severe pulmonary disease or even meningitis, the investigators wrote in MMWR.

Last year, the Infectious Diseases Society of America updated its clinical practice guidelines for the diagnosis and management of valley fever, including treatment suggestions for pregnant women, immunosuppressed patients and those who may otherwise be at increased risk of severe illness, and advice for primary care providers who could mistake the fungal infection for another form of pneumonia.

“Health care providers should be alert for coccidioidomycosis among patients who live in or have traveled to areas where the disease is endemic, especially those who work or participate in activities where dust is generated,” the investigators wrote in MMWR.

According to their report, after several years of decline, the rate of valley fever infections in California surged to 13.7 per 100,000 people in 2016. The 5,372 reported cases were the most since the state began tracking individual infections in 1995, according to the report.

The investigators said the reasons behind the increase are unknown, but possible explanations include “climatic and environmental factors favorable to Coccidioides proliferation and airborne release ... including rainfall after several years of drought and soil disturbance resulting from construction.”

Almost all U.S. cases of valley fever occur in Arizona and California, with similar trends normally observed in the two states. However, this was not the case in 2016, when Arizona experienced a decrease in cases as infections in California rose, the investigators said.

They said patients of African or Filipino descent, pregnant women, older adults and patients with weakened immune systems are at an increased risk of severe disease. Construction workers are also vulnerable to infection and can protect themselves by using personal protective respiratory equipment, according to the report. Previous findings indicate that prison workers may also be at a higher risk.

“To decrease the risk for infection, persons living, working, or traveling in areas where Coccidioides is endemic, especially those at increased risk for severe disease, should limit exposure to outdoor dust as much as possible, including staying inside and keeping windows and doors closed during windy weather and dusty conditions,” the investigators wrote in MMWR. – by Gerard Gallagher


Cooksey GS, et al. MMWR Morb Mortal Wkly Rep. 2017;doi:10.15585/mmwr.mm6631a4.

Galgiani JN, et al. Clin Infect Dis. 2016;doi:10.1093/cid/ciw360.

Disclosure: The researchers report no relevant financial disclosures.