Changing Geographic Distributions of Coccidioides spp. in the United States: A Narrative Review of Climate Change Implications

Abstract

Purpose: Analysis of alterations in the United States prevalence of coccidiomycosis in geographic regions historically considered to not be endemic for the Coccidioides spp. pathogen taken with an evaluation of changing climate patterns within those areas. Methods & Materials: The databases MEDLINE, Google Scholar, PubMed, and CINAHL were searched for English-language sources with combinations of the following keywords: climate change, Coccidioides, distribution, and United States with relevant synonyms. Preference was given within the inclusion criteria to sources published in the past 20 years. The bibliographies of the retrieved publications were also searched. Exclusion criteria included sources relative to areas outside the continental United States. Results: Although Coccidioides species have classically been recognized as endemic to the southwestern United States, isolates have been found far outside this area and recent investigations have demonstrated a growing endemic zone. Ecological and outbreak data supports the conclusion that these findings result from a growing endemic range that is estimated to be as far east as Texas and as far north as Washington State. Investigations point to climate change as the underlying cause primarily via regional climate changes and large dust storms. Conclusion: The geographic distribution of Coccidioides fungus is known to be larger than classically recognized or potentially considered in the formation of diagnostic differentials in the clinical setting. Timely diagnosis, appropriate treatment approaches, and accurate reporting for public health surveillance rely on a recognition of endemic range expansion. Physician education (via medical school curriculums and continuing education offerings), interprofessional team-based approach, and enhancement of surveillance in locations in potentially geographically novel areas are appropriate measures in improving the identification of coccidiomycosis cases.Case studies from local outbreaks and natural disasters support adding coccidioidomycosis to a list of other infectious diseases (e.g., those that are vector borne) whose endemic areas are spreading due to climate change. Recognition of underlying climate change related mechanisms should also prompt steps to reduce environmental spread where mitigation is possible. Current climate model predictions support an expected increase in Coccidioides spp. infection; further research is recommended to clearly define the relationship between climate change and Coccidioides spp. geographic expansion.