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Geographic Distribution of Valley Fever Wider Than Thought

A recent study has shown that outbreaks of Valley fever have a wider geographic distribution than once thought.

Michael Freedman, MD, from the Children’s Hospital of Pittsburgh, Pennsylvania, and colleagues, analyzed data from 47 Valley fever outbreaks and published the results of their study online in the March 2018 issue of Emerging Infectious Diseases, the Centers for Disease Control and Prevention’s (CDC) monthly peer-reviewed public health journal. 

“Most (85%) outbreaks were associated with environmental exposures,” the authors write, and “more than one-third of outbreaks occurred in areas where the fungus was not previously known to be endemic.”

Valley fever, or coccidioidomycosis, is caused by a fungus of the genus Coccidioides. Spores of the fungus are found in the soil in the southwestern United States, south-central Washington, and parts of Mexico and Central and South America.

Individuals become infected by inhaling fungal spores which are stirred into the air by winds or any activities that disrupt the soil. Not everyone who inhales the spores develops Valley fever, but those who do typically have an influenza-like syndrome with cough, shortness of breath, fever, and fatigue.

The disease is reportable in some states, with approximately 10,000 cases reported in the United States each year. However, Valley fever is considered to be largely underdiagnosed, and its epidemiology remains poorly understood. 

In an effort to identify common features and prevention opportunities, Dr. Freedman and colleagues reviewed 47 Valley fever outbreaks worldwide that resulted in 1,464 cases from 1940 to 2015.

They found that 40 (85%) of the outbreaks were associated with environmental exposures, and 33 (83%) of these occurred in the United States. The 2 largest outbreaks accounted for 592 (40%) of cases and occurred in California after an earthquake and a large dust storm.

The remaining 7 outbreaks were associated with nonenvironmental exposures; four of these were related to laboratory exposures, and 2 were health care related (one outbreak was nosocomial, and one occurred through organ transplantation).

Interestingly, almost one-third of all outbreaks (n=12; 32%) occurred in new areas in Arizona, California, Texas, Utah, and Brazil where coccidioidomycosis was not previously known to be endemic. And 4 (11%) outbreaks confirmed suspicions of endemicity in certain areas of Arizona and California.

More than half (n=25; 53%) of outbreaks involved occupational exposures, the authors say: 11 of these were linked to the military, 7 were linked with construction, and 7 to archeology and other field studies.

Although the researchers acknowledge that their findings are limited by the fact that many outbreaks are not recognized, not reported, not investigated, or not published, they stress the need to monitor the locations of Valley fever outbreaks and the conditions in which they occur.

“[I]ncreased attention to outbreak identification and tracking is worthwhile given the continued population growth in coccidioidomycosis-endemic areas, increased settlement at the wildland–urban interface, and the incompletely understood effects of intensifying climate change on Coccidioides,” they write. “Monitoring outbreaks could be critical in identifying new areas of endemicity and high-risk activities.”
Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.
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