Exploring the Distribution of Coccidioides immitis in South Central Washington State

Abstract

ObjectiveOur objective is to describe the environmental conditions associatedwith confirmedCoccidioides immitisgrowth and accumulation sitesin south central Washington in an effort to understand the ecology andidentify additional potential sites across this emerging endemic zone.IntroductionCoccidioidomycosis, commonly referred to as Valley Fever, iscaused by the soil-borne saprophytic fungusC. immitisandposadasii.These species have historically been found in the desert southwest andMexico; however, in 2010 there were three coccidioidomycosis casesidentified in central Washington. Colonization of soils byC. immitishas been confirmed at exposure sites associated with these cases1.Multiple studies have identified a relationship between environmentalconditions andC. immitisgrowth areas2,3,4, but these relationshipshave not been evaluated in Washington. The Washington StateDepartment of Health has been conducting environmental surveillancein an effort to understand the geographic distribution ofC. immitisincentral Washington and the associated risk to humans and animals.Here we describe our environmental surveillance efforts and presentpreliminary findings related to environmental conditions ofC. immitisgrowth areas in central Washington.MethodsWe collected soil samples at potential human exposure sites incentral Washington, as identified through clinical surveillance andpatient interviews. Soil samples were also collected from areasnot associated with human cases by looking for similar soils inareas of interest Soil samples are analyzed by the U.S. Centers forDisease Control and Prevention using real-time PCR that detectsCoccidioides-specific targets. We employed data from the USDA SoilSurvey Geographic (SSURGO) database to describe environmentalconditions associated with positive samples. We used our findingsto identify un-sampled regions of central Washington that couldpotentially supportC. immitisgrowth.ResultsWe detectedCoccidioidesin 13 soil sampling sites at fivelocations withing the region. These detections included locations notpreviously described in central Washington. We identified a bandstretching across central Yakima and Benton counties with similarsoil characteristics to our positive sample sites, which suggests theseregions could potentially support the growth ofC. immitis.ConclusionsCoccidioidomycosis is emerging in south central Washington, andthe ecology and geographic distribution of the pathogen are poorlyunderstood. We found thatC. immitispresents a risk to humans andanimals across a larger region of central Washington than previouslydescribed and highlights a need for continued environmentalsurveillance. The potential growth sites we identified also providea valuable tool for human and veterinary health care providers andpublic health practitioners to understand and mitigate disease risk.