Detection of Coccidioides immitis in Archived Soils from Madera County, California

In the 1970s, archaeologists excavating sites in Madera County, California, which is now submerged by Hensley Reservoir, contracted coccidioidomycosis (Valley fever), a fungal disease caused by Coccidioides immitis. Soil samples from these sites were archived but not processed due to concerns about infectious arthroconidia. This study investigates whether these decades-old samples, stored at room temperature, still contain Coccidioides and pose a risk to researchers and collections managers. We analyzed 176 subsamples using molecular and culture-based methods, with DNA extractions performed in duplicate across two laboratories. Results confirmed the continued presence of Coccidioides DNA, indicating that long-term archived soils can retain infectious potential. Based on these findings, we developed protocols for safe handling of such materials. Our work highlights the intersection of environmental exposure, occupational health, and Coccidioides' persistence in soil. It underscores the need for biosafety measures when handling archived soils from endemic regions, especially those of archaeological interest. Individuals working with these materials, whether in field settings or museum collections, may be at risk of exposure and illness without proper precautions. This study provides a framework for assessing and mitigating risks associated with archived soils and contributes to broader discussions on environmental reservoirs of fungal pathogens. By combining culture-based and molecular approaches, we demonstrate the importance of proactive safety protocols in protecting public and occupational health.