Coccidioidomycosis Exposure Assessed by Skin Testing and Environmental Factors in Baja California, Mexico

Baja California is the second-highest state in Mexico for hospital discharges attributed to coccidioidomycosis (CM), yet epidemiological information on population-level exposure remains limited. To estimate exposure to Coccidioides and assess its association with environmental factors, we conducted intradermal coccidioidin skin testing among 416 residents across nine regions of Baja California. We analyzed 24 environmental variables, including bioclimatic, topographic, and land use indicators. Overall, 31.9% of participants tested positive. Higher odds of exposure were observed in Valle de las Palmas and La Morita. Differences between high- and low-positivity localities were observed in annual precipitation, precipitation during the wettest month, and elevation. High-positivity areas were characterized by annual precipitation ranging from 243 to 311 mm, wettest-month precipitation from 55 to 79 mm, and elevations between 125 and 276 meters above sea level. These findings indicate heterogeneous exposure to Coccidioides across Baja California and highlight the role of environmental factors in shaping transmission risk, supporting the need for strengthened epidemiologic surveillance in high-positivity areas.