Epidemiology

The geographic range of Coccidioides has been derived from clinical cases, soil testing, and on the basis of skin testing performed in 1957 throughout the Southwestern United States (1, 2). The exact ecologic niche remains to be determined. Endemic areas where disease is prevalent include Arizona, California, New Mexico, Nevada, Utah, Washington, Texas, Mexico, and some areas in Guatemala, Honduras, Venezuela, Brazil, Argentina, and Paraguay (3, 4). In the United States, the annual incidence of coccidioidomycosis is variable, but overall is rising, from a rate of 5.3 per 100,000 in 1998 to a rate of 42.6 in 2011 (5). Of these cases reported to the Centers for Disease Control, 66% were from Arizona and 31% from California. Despite the increased incidence, from an analysis of death certificates, the age-adjusted mortality rate from 1990 - 2008 has remained stable at ~0.59 per million person years (6). There were 1,451 coccidioidomycosis-related deaths in California compared to 1,010 in Arizona despite its higher annual reported case rate.

Number of coccidioidomycosis cases and incidence rate, by estimated year of illness onset* — California, 1995–2016

MMWR Morb Mortal Wkly Rep. 2017 Aug 11; 66(31): 833–834

The incidence of coccidioidomycosis in California and Arizona can vary greatly by geographic region, and may be seasonal in pattern. In a yearly summary by the California Department of Health, the overall incidence of coccidioidal infection in the state rose from 4.3 to 11.6 per 100,000 population between 2001 and 2010 (7). In Kern County, however, the rate reported in 2011 was much higher, 241 per 100,000 population (8). Similar increases have been observed in Arizona (9, 10). The reasons for the overall increase are not fully clear, and have been attributed to changing environmental conditions, human activities in endemic areas, changing surveillance methods and definitions, increased numbers of immunosuppressed individuals, and even improved awareness and diagnostic testing rates(11). In endemic regions, the people most affected are construction and farm workers, military personnel, archaeologists, excavators, inmates, and officers in correctional facilities.

Epidemics in endemic regions have occurred after dust storms, earthquakes, and earth excavation where dispersion of arthroconidia is facilitated (9, 12). In Washington State, three cases were recently reported, an area not previously considered endemic; follow-up soil testing showed the presence of Coccidioides immitis, suggesting the geographic range of this organism is larger than previously thought (13, 14). After coccidioidomycosis became a reportable condition, the case rate even in nonendemic regions (eg recent report in Missouri) increased substantially, but many cases were among people who never previously travelled to an endemic region and were diagnosed serologically rather than by culture, PCR or histopathologically (15). Clinical cases of coccidioidomycosis in patients from non-endemic regions are often reported, but frequently a link is established, however brief the transit, to an endemic region (16). There is even a case report of coccidioidomycosis in Hong Kong in a patient who is believed to have contracted the disease by sweeping shipping containers from the US with no other link to the endemic region (17).

REFERENCES

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