Objective To understand and analyze the incidence of high transmission risk of HIV/AIDS and influencing factors in Ningbo, Zhejiang province, and provide evidence for the precise prevention and control of HIV/AIDS.

Methods A cohort study design was used, and local HIV/AIDS cases with low transmission risk identified in Ningbo in March 2017 were included to establish a cohort to conduct annual transmission risk assessment survey until March, 2022. The survey collected the information about general demographic characteristics and laboratory test results of the cases. Cox proportional hazard regression model was used to analyze the incidence of high transmission risk of HIV/AIDS and influencing factors, and the incidence of high transmission risk during follow-up was the outcome variable.

Results A total of 2 672 cases of HIV/AIDS cases were recruited, and 2 371 cases were included in the follow-up, in whom 806 were finally identified as the cases with high transmission risk. The cumulative observation time of the cohort follow-up was 8 615.00 person-years, and the incidence rate of high transmission risk was 9.35/100 person-years. Multivariate Cox proportional hazard regression analysis showed that being man hazard ratio (HR) =1.46, 95% confidence interval (CI): 1.15−1.86, being unmarried (HR=1.42, 95%CI: 1.16−1.73) and being divorced or widowed (HR=1.34, 95%CI: 1.36−1.92) and homosex (HR=1.62, 95%CI: 1.36−1.92) were the risk factors for high transmission risk, and being farmer (HR=0.70, 95%CI: 0.54−0.90) was the protective factor for high transmission risk. In those with high transmission risk identified in the follow up, 39.83% had high-risk sexual behaviors in an average time of 3.25 (1.25−3.25) years, 47.77% were diagnosed with syphilis in an average time of 1.25 (0.25−3.25) years. 3.47% discontinued or stopped treatment in an average time of 1.25 (1.25−2.25) years. The average time when viral load increase or viral load detection interruption occurred was 0.25 (0.25−1.25) years, the differences were all significant (Kruskal- Wallis test=125.231, P<0.05).

Conclusion The incidence rate of high transmission risk of HIV/AIDS was low in Ningbo. After long-term follow-up, some HIV/AIDS cases with low transmission risk had high-risk sexual behavior, diagnosed with syphilis and discontinued antiviral treatment. It is suggested to conduct regular HIV/AIDS transmission risk assessment in the future follow-up management and find the cases with high transmission risk in a timely manner and provide continuous intervention to further reduce the spread of AIDS.