Paper Information

Potential future expansion of Coccidioides into new regions highlights the need for increased surveillance in the USA. Hospital data can be used to estimate Valley fever risk wherever surveillance data are scarce.

In this modelling study, we used generalised additive models to construct two Coccidioides suitability models at the county and ZIP code tabulation area (ZCTA) scales. The county model used public health surveillance data from 2010 to 2019 provided by the US Centers for Disease Control and Prevention, whereas the ZCTA model was based on emergency department visit data. We compared predicted suitable areas to assess the utility of hospital data in estimating Coccidioides suitability and projected future suitability using data from 33 global climate models for 2050, 2075, and 2100.

The ZCTA model had better out-of-sample predictive performance for identifying endemic areas than the county model (area under the precision-recall curve: 0·81 vs 0·57), including higher specificity (0·84 vs 0·52). Both models identified potential suitable areas for the fungi beyond California and Arizona, including Texas, where coccidioidomycosis is currently not a notifiable disease. Additionally, both models projected a similar future northward and eastward shift in Coccidioides suitability, with these shifts exacerbating under higher levels of warming. Under Shared Socioeconomic Pathway 2-4.5, we estimated that non-endemic ZCTAs containing 23 million (95% uncertainty interval 8-34) people could become suitable for Coccidioides by 2050, rising to areas containing 30 million (21-43) by 2100.

Coccidioides are fungi endemic to western USA and are estimated to cause more than 200 000 symptomatic cases of coccidioidomycosis, also known as Valley fever, annually. Endemicity is influenced by environmental conditions, including precipitation, temperature, and soil composition. As environmental conditions change in the future, the geographical distribution of the fungi can be altered.

US National Institutes of Health.