Mapping the Geographic Distribution of Dimorphic Mycoses Using a US Commercial Insurance Database

Background. The dimorphic mycoses (DMs) histoplasmosis, blastomycosis, and coccidioidomycosis are classically thought to be geographically restricted to specific regions of the United States. The current scientific consensus is that these geographic boundaries are expanding, but the extent of this expansion remains uncertain. Methods. This study is a retrospective analysis of >21 million (annually) commercially insured individuals within the United States during 2007–2016. Diagnosis of histoplasmosis, coccidioidomycosis, and blastomycosis were identified using International Classification of Diseases, Ninth/Tenth Revision codes within the Merative MarketScan database. Results. There were 37 513 histoplasmosis, 14 987 coccidioidomycosis, and 2207 blastomycosis diagnoses during 2007–2016 within 387 Metropolitan Statistical Areas. DMs were consistently diagnosed outside their historical hyperendemic regions. Conclusions. New diagnoses of histoplasmosis, coccidioidomycosis, and blastomycosis were routinely made outside their historically defined regions of endemicity. While exposure to hyperendemic regions remains a risk factor for developing a DM infection, clinicians should consider testing any patient presenting with a compatible clinical syndrome, regardless of their geographic history. Increased suspicion of DM infection will lead to fewer missed or delayed diagnoses, thereby improving patient outcomes.