Objective  To analyze the characteristics of HIV-1 molecular network in the people aged ≥50 years from July 2018 to June 2020 in Shaoxing, Zhejiang province, explore the risk factors associated with HIV-1 transmission network and provide evidence for the effective intervention.

  Methods  A total of 147 samples of newly reported HIV-1 positive cases were consecutively collected, the pol gene fragments of HIV-1 were amplified by reverse transcription polymerase chain reaction (PCR) and nested PCR. The phylogenetic tree constructed to analyze the molecular transmission network for subtypes and different gene distances. The factors associated with the subjects entering network and characteristics of cluster were further analyzed.

  Results  Four subtypes were found in the samples, CRF07_BC (76, 51.70%) were the major subtypes, followed by CRF01_AE (36, 24.49%), CRF08_BC (33, 22.45%) and B (2, 1.36%). A total of 74 sequences entered the network, with an entry rate of 50.34%, forming 12 clusters with the number of individuals in the cluster ranging from 2 to 30. The analysis on the factors associated with entering network showed that those with lower education level and awareness rate of AIDS knowledge, paying no attention to AIDS topics, commercial sexual behavior without condoms and female sex workers with payment less than 50 yuan at each sex were more likely to be found in HIV-1 molecular networks. The results of multivariate logistics model analysis showed that female sex workers with payment less than 50 yuan more easily entered molecular network. CRF07_BC had the highest cluster proportion (30, 40.54%) and formed a large cluster with 30 cases, most of these cases lived in and near Chengnan Street of Yuecheng district and had commercial sex. CRF01_AE had a cluster of 7 cases, including 1 female sex worker, and these cases lived in and near Qixian Street of Keqiao district. There were twelve positive couples in all clusters, the family transmission were caused by male commercial sex.

  Conclusion  The genotypes of HIV-1 in the people aged ≥50 years in Shaoxing have become complex, the risk factors associated with transmission network included lack of AIDS prevention knowledge and unprotected sex with lower grade female sex workers. The geographical distribution of cluster cases was obvious, in order to effectively control the spread of AIDS, more attention should be paid to intervention and HIV screening in areas with case clusters.