A transmission relationship investigation of HIV infection through male-to-male sex among a case of left-behind children with heterosexual orientation in Zhejiang Province of China.

Objective: This study seeks to trace the source of HIV infection in a male adolescent (P1) with a newly recognized heterosexual orientation in Zhejiang Province on August 23, 2019. Methods: An in-depth epidemiological interview was conducted with P1 and all sexual partners. For HIV-infected partners, sequential partner tracing was performed until no new HIV cases were detected. The survey assessed high-risk sexual behavior, HIV testing and treatment history, and demographic details. Serum samples were collected for HIV antibody testing, and plasma samples from HIV-positive individuals were taken before antiviral therapy. HIV DNA was extracted, and specific gene regions were amplified, cloned, and sequenced. Phylogenetic trees were created using MEGA V6.0 to identify HIV subtypes, calculate genetic distances, and analyze genetic associations. Genetic similarity was calculated using BioEdit V7.2.0. Results: The results indicated that P1, a 16-year-old male dropout and left-behind child, first tested positive for HIV-1 antibodies on August 23, 2019. P1's heterosexual partner, W1, is HIV-negative. P1 had a same-sex partner, P2, who tested positive on November 9, 2018. P2 is an adult, did not communication with P1 about his HIV status and had unprotected sex with P1 before P1 tested HIV positive. P2 reported seven male sexual partners in same district, P1 was one of them and all other sexual partners were HIV-negative. Among these seven partners, two were with divorced parents, six were dropouts, and three were left-behind children. Phylogenetic analysis revealed that both P1 and P2 had CRF01_AE/CRF55_01B/CRF07_BC recombinant HIV, with genetic similarities in the gag, pol, and env regions of 98.8, 99.5, and 98.8% for P1 and 99.0, 99.7, and 99.0% for P2. The genetic similarity between two samples of P2 in these regions was 98.7, 99.6, and 99.9%. In the gag and env gene regions, interwoven branching patterns were observed, which are indicative of shared transmission chains. For the pol gene region, the C1 paraphyletic sequences of P1 and P2 clustered within the same evolutionary branch, with a bootstrap value of 100% and a mean genetic distance of 0.003 within this cluster. Conclusion: Epidemiological and phylogenetic analyses concluded that P1 contracted HIV through unprotected sex with an HIV-positive P2 who did not disclosure his HIV infection.