What are the coccidioidal infection rates in endemic areas of 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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In areas of highest endemicity, the infection rate is approximately 2-4% per year. The prevalence in endemic areas has varied over time; the disease affects 30-40% of the population within the endemic regions of California and Arizona. [10] This figure is lower than findings from epidemiologic studies performed 50 years ago, when 68% of the population was found to have skin tests positive for coccidioidal antigens. Positive skin test results are related to the duration of residence in endemic areas and to occupational and recreational exposure to dust.

The number of cases of coccidioidomycosis in endemic regions rises sharply in the late summer and early fall, after the soil dries. At that time, soil disturbances, either natural (wind) or man-made (agricultural endeavors, construction, archaeological excavations), are likely to send Coccidioides spores airborne, enhancing the likelihood of its inhalation. In particular, outbreaks have been documented after earthquakes (eg, the 1994 Northridge earthquake in California) and wind storms.

Arizona, where coccidioidomycosis is a reportable condition, has the greatest number of cases. This likely represents symptomatic cases only. More than 5,000 cases are reported annually in Arizona, and the state has noted a steady increase in cases, with 7 cases per 100,000 persons in 1990, increasing to 15 cases per 100,000 persons in 1995 [19] and an estimated 75 cases per 100,000 persons in 2007.

In California, the number of annually reported coccidioidomycosis cases more than tripled from 2000-2006, rising from 2.4 to 8 cases per 100,000 population. [20] The annual incidence was highest in Kern County (150 cases per 100,000 population), with the hospitalization rate highest among non-Hispanic blacks, increasing from 3 cases to 7.5 cases per 100,000 population.

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