Risk factors for syphilis among newly admitted prisoners: A case–control study

BACKGROUND: Syphilis remains a major global public health concern in various groups, including people in prisons, where the burden is substantial. This study aimed to identify factors associated with syphilis infection among newly admitted prisoners in a province of Thailand. METHODS: A case-control study was conducted among newly admitted prisoners in three correctional facilities. Cases and controls were randomly selected from newly admitted prisoners who had undergone syphilis screening at prison entry between 01/04/2025 and 30/09/2025. Data were collected using validated data collection instruments, including case record forms and structured questionnaires. Multivariable logistic regression analysis was used to identify factors associated with syphilis infection among newly admitted prisoners, with statistical significance set at p-value < 0.05. RESULTS: A total of 51 cases and 204 controls were included in the study. In multivariable logistic regression analysis, homosexual or bisexual orientation (adjusted odds ratio [AOR] = 9.59; 95% confidence interval [CI]: 1.81-50.92), a history of sexually transmitted infections (AOR = 38.03; 95% CI: 10.46-138.31), anal intercourse (AOR = 4.47; 95% CI: 1.05-19.12), sexual intercourse without condom use (AOR = 13.82; 95% CI: 3.38-56.43), and injection drug use (AOR = 45.60; 95% CI: 2.88-722.12) were significantly associated with syphilis infection among newly admitted prisoners. CONCLUSIONS: Prison entry represents a critical opportunity for syphilis screening. Risk-based screening strategies targeting individuals with high-risk sexual behaviors and substance use should be prioritized to reduce syphilis transmission in correctional facilities.