What is the incidence of coccidioidomycosis in the US?

Updated: Aug 27, 2019
  • Author: Duane R Hospenthal, MD, PhD, FACP, FIDSA, FASTMH; Chief Editor: Michael Stuart Bronze, MD  more...
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The exact incidence of coccidioidal infections can only be inferred because approximately 60% of those infected are asymptomatic or have subclinical disease and never come to medical attention. An estimated 150,000 infections occur annually in the United States. This estimate is higher than the 100,000 cases per year previously cited in the literature and reflects population increases in southern Arizona and central California, where the organism is endemic. [12, 7] From 1988-2011, the incidence of coccidioidal infections in Arizona, California, Nevada, New Mexico, and Utah increased from 5.3 per 100,000 to 42.6 per 100,000. [18]

Approximately 25,000 new, clinically evident cases of coccidioidomycosis are reported annually in the United States. As many as 75 deaths per year result from the infection.

Based on skin test data, 80% or more of residents living in endemic areas for 5 years or longer will have a positive coccidioidin skin test result. The prevalence of positive skin test results ranges from 50-70% in the southwestern United States and increases with age.

Several sharp upsurges in the incidence have occurred. The western migration of the 1930s and the influx of military personnel in the 1940s triggered notable increases. In 1978, the first true epidemic occurred after an unprecedented dust storm that originated in the lower end of the San Joaquin Valley, quadrupling the incidence of disease.

A coccidioidal epidemic occurred in California in 1991-1994. In 1992, this outbreak produced a peak of approximately 4200 cases, an increase of more than 14-fold from baseline. One explanation for the epidemic is that it occurred after a 5-year drought that was terminated by above-average rainfall. This rainfall allowed dormant arthrospores to germinate and to be carried aloft by summer winds. At the same time, a marked influx of disease-naive individuals into the area further set the stage for the epidemic.

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