Epidemiology

The aetiological agents of coccidioidomycosis, Coccidioides immitis and C posadasii, inhabit ecological niches found only in the western hemisphere (areas of low precipitation), primarily in the southwestern deserts of the US (California, Arizona, New Mexico, and western Texas) and northern deserts of Mexico.[3][4]​​ They are also endemic in limited areas of Utah, Nevada, and eastern Washington state, as well as Central and South America. Coccidioidomycosis is an infection identified primarily in people residing within these areas; cases outside the endemic areas may be identified in visitors returning to non-endemic areas. An estimated 150,000 cases of coccidioidomycosis occur in the US annually, although many of these are misdiagnosed and unreported.[5] In 2019, approximately 20,000 cases were reported to the Centers for Disease Control and Prevention (CDC), most of which were among people living in Arizona or California.[6] One retrospective analysis of data from 2007 to 2016 found that coccidioidomycosis was diagnosed in significant numbers outside the historical geographic distribution, with 69% of the US states above the clinically relevant threshold for coccidioidomycosis in at least one county.[7]​ The number of reported cases in the US varies year-to-year, but continues to increase yearly.[4] This variation is not fully understood, but suggested reasons include changes to: the number of people exposed to Coccidioides (owing to travel or relocation); environmental factors affecting fungal growth and circulation (such as temperature and rainfall); and the way cases are detected and reported.[6]

Coccidioidomycosis is acquired when airborne fungal arthroconidia (spores) are inhaled; therefore, occupational (e.g., construction, digging) or recreational (e.g., gardening) activities that increase the likelihood of dust inhalation also increase the likelihood of infection. Outbreaks have been associated with activities such as archaeological excavation, construction, and military training exercises.[8]​ They have also been reported in people who fight wildfires.[9]​ Climatic variables‚ such as precipitation, drought, temperature, wind speed, and dust‚ also affect the amount of airborne spores.[3]

Males are more likely to acquire infection; this may be due to increased likelihood of occupational or recreational dust exposure.[10] Race is a strong risk factor for developing severe and disseminated infection but not for acquisition of infection.[3] African-Americans and Filipinos have the highest risk for dissemination, approximately 10 to 175 times greater than other races.[3][11]​​​ The evidence is poor on whether there exists an increased risk of dissemination for Asians, Hispanics, and American Indians. It is likely that race per se is not the predisposing risk but rather the associated genetic makeup that dictates the immune response. People with immunosuppression, such as organ transplant recipients, people with HIV, or pregnant people, are also at increased risk for developing disseminated disease.[3][8]​​​​[11][12][13]​​​​ People aged ≥65 years, people with diabetes, people who smoke, and people with high inoculum exposure are at increased risk of developing severe pulmonary complications.[8]

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