Demographic patterns of syphilis seropositivity in Mongolia: a nationwide cross-sectional serosurvey, 2022–2024

Syphilis remains a significant public health concern in Mongolia. We estimated syphilis seropositivity and examined the demographic and regional patterns among young adults screened through Mongolia’s national Prevention, Early Detection, and Screening Program. We analyzed de-identified screening records of individuals aged 18–34 years who underwent syphilis screening between May 1, 2022, and May 1, 2024. Reactive treponemal screening results were linked to confirmatory diagnostic data. Confirmed cases were classified as early syphilis (International Classification of Diseases 10th revision codes [ICD-10]: A51) or latent/unspecified syphilis (A53). Seropositivity was summarized by demographic group, and univariable logistic regression assessed associations with A51 and A53. Overall, 34,111 individuals were screened, 28,048 participants were included in the analysis, 1,454 had reactive treponemal screening results, and 167 had a recorded confirmed syphilis diagnosis, representing 11.5% of reactive screening results and 0.60% of the analytical population. Of the confirmed cases, 75 (44.9%) were classified as early syphilis (A51) and 92 (55.1%) as latent or unspecified syphilis (A53). The overall proportion of confirmed syphilis diagnoses was 0.49% among women (73/14,861) and 0.71% among men (94/13,187). In univariable logistic regression, sex and region were significantly associated with early syphilis. Males had higher odds of early syphilis than females. Compared with Khangai, the odds of early syphilis were significantly lower in Central, Gobi, and Ulaanbaatar. For latent or unspecified syphilis, only Central had significantly higher odds compared with Khangai. Among young adults included in the analytical dataset, the proportion and diagnostic classification of confirmed syphilis diagnoses varied across demographic and geographic groups. These findings support careful interpretation of reactive screening results and strengthening diagnostic confirmation, follow-up, and linkage to care.