Assessment of seroprevalence of Mpox virus infection among sex workers in Chiang Mai, Thailand Umer, M. Chawansuntati, K. Wipasa, J. Jindaphun, K. Kotemul, K. Thant, Y. M. /Ngo-Giang-Huong, Nicole Khamduang, W. Hongjaisee, S. Mpox virus Seroprevalence Sex workers In-house ELISA E8L antigen Thailand Objectives: The 2022 global Mpox outbreak revealed major surveillance gaps, particularly among marginalized populations such as sex workers, whose role in undetected MPXV transmission remains poorly understood. This study aims to assess the seroprevalence of MPXV IgG antibodies and identify associated risk factors among sex workers in Chiang Mai, Thailand. Methods: In this cross-sectional study, 262 sex workers recruited from March to December 2022 were tested for prior MPXV exposure using an in-house indirect ELISA targeting the recombinant MPXV E8L antigen. Logistic regression models were used to identify demographic and behavioral factors associated with seropositivity. Results: MPXV IgG seroprevalence was 4.6% (12/262). Seropositivity was significantly higher among males than females (5.2% vs 4.0%, P = 0.011). In multivariable analysis, male gender (OR = 3.23, 95% CI: 1.109.47, P = 0.032), blood transfusion history (OR = 4.40, 95% CI: 1.35-14.25, P = 0.013) and sharing sharp objects with others (OR = 4.55, 95% CI: 1.12-18.48, P = 0.034) were significantly associated with Mpox seropositivity. Conclusion: Our findings reveal undetected MPXV circulation among Chiang Mai sex workers. The identified risk factors suggest overlapping parenteral and sexual vulnerabilities, emphasizing the need for integrated surveillance and targeted interventions. 2025 text https://www.documentation.ird.fr/hor/fdi:010095313 fdi:010095313 Umer M., Chawansuntati K., Wipasa J., Jindaphun K., Kotemul K., Thant Y. M., Ngo-Giang-Huong Nicole, Khamduang W., Hongjaisee S.. Assessment of seroprevalence of Mpox virus infection among sex workers in Chiang Mai, Thailand. 2025, 160, 108041 [9 p.] EN THAILANDE CHIANG MAI