What's Behind the Increasing Rates of Coccidioidomycosis in Arizona and California?

The number of cases of symptomatic coccidioidomycosis reported in the endemic regions of California and Arizona has increased over the past two decades. In California, the southern San Joaquin Valley has seen a dramatic increase, with rates of symptomatic illness of more than 150 per 100,000 of population in Kern County. In Arizona, almost 5,000 cases are now reported yearly. In contrast to California, the coccidioidal endemic region in Arizona is also the most populous region of the state, and Arizona now accounts for 60% of all cases reported in the United States. Reasons for these increases appear to be multifactorial. Possible etiologies include climate change, changes in local exposure, an increase in the number of individuals susceptible to infection living in the endemic region, and increased testing and reporting. None of these factors are mutually exclusive and none has been clearly established as the etiology for the increase.