Prevalence of syphilis among people living with HIV who attend a large urban antiretroviral therapy clinic in Panama: a cross-sectional epidemiological study

Background: Syphilis is a serious global public health challenge. Despite prior progress in syphilis control, incidence has been increasing in recent years. Syphilis is a common coinfection among people living with HIV (PLHIV). In Panama, few data describe syphilis prevalence among PLHIV. We describe syphilis antibody and high-titer (>= 1:8) active syphilis prevalence and associated factors among individuals who attended an antiretroviral clinic. Methods: A cross-sectional study was undertaken during February-March 2022 and September-October 2022 for adults (>= 18 year) assigned male and female at birth, respectively. Participants provided peripheral blood samples and self-administered a questionnaire. Samples were screened using immunochromatography; antibody-positive samples were tested using rapid plasma regain to 1:512 dilutions. Logistic regression was used to identify factors associated with syphilis antibody and high-titer active syphilis. Results: In all, 378 participants gave blood samples; 377 individuals participated in the questionnaire (216 self-reported male sex [males], 158 female [females], and three intersex individuals). Median age was 36 years (interquartile range: 28-45 years). Overall, syphilis antibody prevalence was 32.3% (122/378) (males, 50.7% [108/2013]; females, 5.7% [9/158]; intersex individuals, 100.0% (3/3)], p < 0.01. High-titer active syphilis was found among 24.6% (n = 30) of samples with positive antibody test (males 27.8% [n = 30], females 0.0% [0/9], intersex individuals 0.0% [0/3]). Antibody positivity was associated in the multivariable model with males (50.7%, AOR = 24.6, 95%CI: 1.57-384.53). High-titer active syphilis was associated with younger participant age (18-30 years, 13.2%, OR = 4.82, 95%CI: 1.17-19.83); 31-40 years, 7.8%, OR = 4.24, 95%CI: 1.04-17.21 versus 3.2% >40 years), homosexual identity (16.0% OR = 34.2, 95%CI: 4.50-259.27 versus 0.6% among heterosexual identity); in the multivariable model, associated with sexual identity (bisexual 19.1%, AOR = 10.89, 95%CI: 1.00-119.06) compared to heterosexual identity (0.6%) and weakly associated with concurrency (>= 1 ongoing sexual relationships, 15.9%, AOR = 3.09, 95%CI: 0.94-10.14). Conclusion: This study found very high prevalence of syphilis antibodies and high-titer syphilis among PLHIV in Panama. Those most affected are males, younger in age, those who practice concurrent sexual relationships, and those who reported homosexual and bisexual identity. Targeted interventions should include repetitive testing and treatment, especially among individuals who may be at increased infection risk.