Objective To analyze the characteristics of sexual behaviors and transmission network of newly confirmed human immunodeficiency virus (HIV)/acquired immuno deficiency syndrome (AIDS) cases caused by heterosexual transmission in people aged ≥50 years in Jinhua, Zhejiang province, from 2020 to 2022, and provide evidence for the precise prevention and control of AIDS.

Methods An epidemiological survey was conducted in newly confirmed HIV/AIDS cases caused by heterosexual transmission in people aged ≥50 years in Jinhua from 2020 to 2022. Meanwhile, blood samples from the newly diagnosed HIV infection cases before antiviral treatment were collected. Pol gene was amplified by nucleic acid extraction and PCR, sequenced with software Sequencer 5.0, and phylogenetic tree was constructed by using software MEGA 6.0, and software Cytoscape 3.6.0 was used to establish HIV molecular transmission network.

Results In the 517 HIV/AIDS cases caused by heterosexual transmission in Jinhua, 369 were infected more than 1 year ago (71.37%), 309 were local infections (59.77%), and 242 were infected through commercial heterosexual behaviors (46.81%), 213 were infected through non-marital and non-commercial heterosexual behaviors (41.20%), and 62 were transmitted by their spouses (11.99%). A total of 410 blood samples were collected, and 369 sequences were successfully obtained. A total of 14 subtypes of HIV-1 gene were detected, with CRF07-BC (179 cases, 48.51%), CRF01-AE (98 cases, 26.56%), CRF08-BC (58 cases, 15.72%) as the main subtypes, and 165 sequences were used in the molecular network, forming 40 clusters. The results of multivariate analysis showed that the HIV-1 clustering rate was higher in age group ≥60 years compared with age group of 50-59 years (OR=1.70, 95%CI: 1.04−2.79, and in the testing of spouses or sexual partners of positive individuals compared with clinical detection (OR=3.68, 95%CI: 1.32−10.22). The HIV-1 clustering rate was lower in those with education level at or above senior high school compared with those with education level of primary school or illiteracy (OR=0.41, 95%CI: 0.18−0.90). There were 8 large clusters, accounting for 49.09% (81/165) of all cluster cases, with C1 and C2 mainly found in the cases with commercial heterosexual behaviors involving female sex workers (FSWs); C3, C5, C6, and C8 mainly found in the cases with commercial heterosexual behaviors involving no FSWs, C4 found in the cases with non-marital and non-commercial heterosexual behaviors with same infected man, causing transmission in married couples and fixed sexual partners; The transmission mode of C7 was found in the cases with commercial heterosexual behaviors with another HIV-infected man, resulting in 4 non-marital and non-commercial heterosexual partners being infected.

Conclusion Commercial heterosexual behavior as well as non-marital non-commercial heterosexual behavior coexisted in the HIV infection cases aged ≥50 years infected through heterosexual contacts in Jinhua. The subtypes of HIV- 1 detected were complex. The proportion of local infections in large clusters was relatively high, with obvious area specific clustering and transmission across counties and districts. Efforts should be made to strengthen interventions for key populations, areas and places, and strengthen the detection and tracing survey in individuals aged ≥50 years.