Exposure to Coccidioides spp. and silent infection in Sonora, Mexico: a cross-sectional serological and environmental analysis

Abstract Coccidioidomycosis is an endemic fungal disease in arid regions of the Americas, yet population-level exposure in Mexico remains poorly defined. This study aimed to evaluate the frequency and spatial distribution of asymptomatic individuals with anti-Coccidioides IgG antibodies residing in different municipalities of Sonora, Mexico, and to evaluate the environmental factors associated with the seropositivity presented. A cross-sectional serosurvey was conducted using 534 serum samples collected from 15 laboratories at different municipalities of Sonora. Anti-Coccidioides IgG antibodies were detected using a commercial enzyme immunoassay. Seroprevalence was analyzed by demographic characteristics, and to evaluate whether environmental conditions differed between municipalities with and without evidence of Coccidioides spp. exposure, mean values of 19 bioclimatic variables were calculated. Overall, IgG seropositivity was 7.3%, with an additional 15% showing indeterminate results. Higher seropositivity was observed among young adults and in individuals that reported no travel to endemic regions in the United States of America. The Mann–Whitney U test identified a significant difference only for temperature seasonality (BIO4) between municipalities with and without seropositive individuals; this difference remained significant after correction for multiple comparisons. These findings provide serological evidence of exposure to Coccidioides spp., in nine municipalities of Sonora. The indeterminate percentage of 15% in an area considered endemic is striking and given that the chosen test is designed for diagnosis, lower cut-off points should be considered for serological surveillance or prevalence studies in asymptomatic populations to provide more information on the hidden burden of coccidioidomycosis in endemic regions.