HIV, syphilis, and gonorrhea co-infection and associated factors among adolescents and young adults aged 15-24 years in Ningbo, China, 2005-2024

Haibo Jiang¹Xing Zhang²Lixia Ye¹Shiwen Tan¹Kun Chu¹Zehao Ye¹Zhixin Zhu¹Chengliang Chai^3*Yi Chen^1*

• ¹Ningbo Municipal Center for Disease Control and Prevention, Ningbo, China
• ²Quzhou City Center for Disease Control and Prevention, Quzhou, China
• ³Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou, China

Background: Sexually transmitted infections (STIs), including HIV, syphilis, and gonorrhea, have exhibited a rising trend among adolescents and young adults aged 15-24 years in China, presenting a major public health concern. This age group faces heightened risks due to behaviors like unprotected sex, multiple partners, and online dating, alongside limited access to healthcare services. Monitoring long-term trends and factors associated with STI co-infections is essential for developing effective prevention and intervention strategies. Methods: Historical data on newly reported syphilis and gonorrhea cases in Ningbo from January 1, 2005, to December 31, 2024, were retrieved from the China Disease Prevention and Control Information System. Cases with final review dates between 2005 and 2024 and reported in Ningbo were selected and matched with concurrent case data from the Comprehensive HIV/AIDS Prevention and Control Information System to investigate factors influencing co-infections with two or more STIs (syphilis, gonorrhea, or HIV) among individuals aged 15-24 years. Chi-square tests for trend were employed to assess temporal patterns in HIV, syphilis, and gonorrhea epidemics, while multivariate logistic regression models were used to evaluate factors associated with STI co-infections. Results: From 2005 to 2024, reported cases of HIV, syphilis, and gonorrhea among adolescents and young adults aged 15-24 years in Ningbo totaled 1,576 (6.0%), 14,623 (55.4%), and 10,204 (38.6%), respectively. The reported epidemics of HIV, syphilis, and gonorrhea in this demographic exhibited a significant upward trajectory over the period (linear regression analysis, P<0.05). Over the 20-year span, the reported HIV incidence rate demonstrated an overall increasing trend (trend χ² = 11.735, P < 0.001). The reported prevalence of HIV, syphilis, and gonorrhea co-infections in this population was 4.9% (1,304/26,403). Reporting year (2015–2024 vs. 2005–2014: aOR=11.637, 95% CI: 9.740–13.905), Gender, occupation, household registration, and sample source were significant predictors of STI co-infections (P<0.05). Conclusion: Targeted interventions should prioritize males, those in high-risk occupations (e.g., housework, unemployment, detention, commercial services, students, or medical personnel), and individuals with non-local (out-of-province) household registration, through enhanced STI health education, behavioral interventions, and expanded provider-initiated testing and counseling (PITC) to curb the upward trends in HIV and STI epidemics.