Molecular transmission network reveals CRF08_BC-driven clusters of HIV-1 among low-education older adults linked to female sex workers in Taizhou, China.

BACKGROUND

The demographic structure of China's HIV-1 epidemic is rapidly shifting toward an aging population. This study aims to analyze the molecular transmission network characteristics of newly diagnosed HIV-1 infected individuals aged 50 and above in Taizhou, China, by combining sociodemographic information.

METHODS

Plasma samples were collected from newly diagnosed HIV-1 patients aged ≥50 years who were not receiving antiretroviral therapy (ART) in Taizhou between 2023 and 2025. HIV-1 subtypes were determined and pairwise genetic distances were calculated based on the HIV-1 pol gene sequences amplified by nested PCR and sequenced by Sanger sequencing. A molecular transmission network was constructed using a genetic distance threshold of 0.010. Logistic regression was subsequently used to identify factors associated with molecular clustering.

RESULTS

Of the 506 samples, 473 (93.5%) were successfully sequenced. The predominant HIV-1 subtypes identified were CRF07_BC (34.0%), CRF08_BC (33.8%), and CRF01_AE (23.5%). Univariate analysis showed that molecular clustering was associated with marital status, education level, heterosexual transmission, and viral subtype. Subsequent multivariate analysis revealed that clustering was significantly correlated with heterosexual contact (aOR = 2.71, 95%CI: 1.46-5.25) and infection with either the CRF08_BC (aOR = 5.90, 95%CI: 3.39-10.46) or CRF07_BC (aOR = 1.85, 95%CI: 1.10-3.14) subtypes. Overall, 264 cases (55.8%) formed 64 distinct molecular clusters, comprising 6 large clusters and 58 small clusters. Notably, four of the six largest clusters belonged to the CRF08_BC subtype. Within the CRF08_BC clusters, 95.2% (120/126) of individuals had junior middle school education or lower, and female sex workers (FSWs) were identified in the two largest clusters. Additionally, a large cluster of 11 individuals comprising the minor subtype CRF85_BC was detected.

CONCLUSION

Molecular transmission networks and sociodemographic data indicate that older, less-educated individuals are facilitating the spread of the HIV-1 CRF08_BC subtype in Taizhou via contact with FSWs. Therefore, targeted interventions focusing on elderly men with low education levels are essential.