Prevalence and associated factors of HIV and syphilis infection among MSM: a cross-sectional study in Shandong Province, China

Syphilis and human immunodeficiency virus (HIV) remain major sexually transmitted infections and pose significant public health challenges worldwide. Despite sustained control efforts, syphilis has re-emerged in many regions, and HIV prevalence remains high, particularly among men who have sex with men (MSM). A cross-sectional study was conducted among MSM aged ≥ 16 years in Shandong Province, China, from April to July 2022 across 11 municipalities (Jinan, Qingdao, Zibo, Yantai, Rizhao, Weifang, Binzhou, Dezhou, Heze, Jining, and Linyi). Participants were recruited using snowball sampling and internet-based outreach, with a target of 400 participants per site. A standardized questionnaire from the Chinese CDC HIV Sentinel Surveillance Programme was used to collect data on demographic characteristics, sexual behaviors, drug use, and pre-exposure prophylaxis (PrEP) use. Additionally, 5 mL of venous blood was collected from each participant for HIV and syphilis testing using standard laboratory procedures. A total of 4416 MSM who met the inclusion criteria were enrolled in this study. The prevalence of HIV infection was 2.74% (121/4416, 95% CI: 2.30–3.26), and the prevalence of syphilis infection was 3.22% (142/4416, 95% CI: 2.73–3.78). The mean age of the participants was 32.03 ± 9.20 years, and 51.59% were aged > 30 years. 2215 participants (50.16%) had a college-level education or higher. 90.59% participants reported using the internet or dating applications as their primary means of seeking male partners. Univariate analyses identified several factors associated with differences between HIV-positive and HIV-negative participants, as well as between syphilis-positive and syphilis-negative participants. In multivariable analyses, self-risk perception was associated with HIV infection (aOR = 2.473, 95% CI: 1.654–3.698). Anal sex in the past 6 months (aOR = 2.816, 95% CI: 1.012–7.833) and having multiple sexual partners in the past 6 months (aOR = 2.032, 95% CI: 1.302–3.170) were also associated with increased odds of HIV infection. Condom use during the last anal intercourse (aOR = 0.393, 95% CI: 0.264–0.583) and PrEP use (aOR = 0.082, 95% CI: 0.011–0.594) were associated with reduced odds of HIV infection. For syphilis infection, self-risk perception was positively associated with syphilis infection (aOR = 1.729, 95% CI: 1.156–2.586), whereas a higher frequency of condom use in the past 6 months was associated with lower odds of syphilis infection (aOR = 0.665, 95% CI: 0.463–0.957). Not using drugs was associated with a lower likelihood of syphilis infection compared with drug use (aOR = 0.515, 95% CI: 0.353–0.750). In addition, history of STDs was strongly associated with increased odds of syphilis infection (aOR = 10.761, 95% CI: 7.239–15.996). The prevalence of HIV and syphilis among MSM in Shandong Province remained relatively low; however, both infections continue to represent important public health concerns in this population. The two infections showed both shared and distinct associated factors, suggesting heterogeneous risk profiles. These findings highlight the need for integrated prevention strategies, including targeted behavioral interventions, expanded PrEP coverage, routine STI screening, and tailored services for MSM with a history of drug use or prior STDs, to effectively reduce the burden of HIV and syphilis in this population.