Risk Factors For Valley Fever Or Coccidioidomycosis

Coccidioides infections occur mostly in regions where the mold is present in the soil including Southern California, Arizona, New Mexico, western Texas, Northern Mexico, and arid regions of South America (Johnson, Gaab et al. 2014).

A recent study in Antelope Valley in Northern Los Angeles County, NW San Bernardino County, and eastern Kern County in California examined the incidence of coccidioidomycosis between 1999 and 2014 (Colson, Vredenburgh et al. 2017).

This area has undergone extensive development during this period including the construction of many homes, businesses, roads, and solar farms. Such land development frequently caused dust storms and increased levels of airborne particulates (as measured by particulates smaller than 10 microns or PM10). In addition, strong Santa Ana winds can frequently cause dust to travel for hundreds of miles. A study of 42 dust samples in the Antelope Valley found that 17 (40%) were positive for presence of Coccidioides immitis. Analysis of coccidioidomycosis cases in north Los Angeles Country reported that increasing land use and increasing outdoor levels of small particulates (PM10) were significantly associated with higher number of cases of Valley Fever Cases/ coccidioidomycosis.
 

Many areas of the Southwestern USA have been undergoing cycles of long drought accompanied by occasional periods of heavy rain. Other research cited in the Colson paper have linked significantly higher levels of airborne Coccidioides and rates of human Coccocidioides infections with periods of wet winters coupled by dry summers- as compared period of long term wet periods or dry periods. The wet winters allow for large Coccidioides growth while the dry summers increase dusty conditions which spreads airborne Coccidioides spores. 

Dust control measurements during construction and soil moving operations and use of masks can be helpful in preventing inhalation and infection of Coccidioides.  
 

References / Sources

Johnson, L., et al. (2014). “Valley fever: danger lurking in a dust cloud.” Microbes Infect 16(8): 591-600.

Colson, A. J., et al. (2017). “Large-Scale Land Development, Fugitive Dust, and Increased Coccidioidomycosis Incidence in the Antelope Valley of California, 1999-2014.” Mycopathologia.

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