Phylogenetic analysis and transmission networks highlight the role of older adults in the transmission of HIV-1 in northern Zhejiang, China.

BACKGROUND

In China, human immunodeficiency virus (HIV) poses a significant challenge to older heterosexual adults. This study explored the transmission dynamics of HIV infection among older adults in northern Zhejiang Province, China using phylogenetic analysis and transmission networks.

METHODS

HIV pol sequences without any antiretroviral therapy were obtained from newly diagnosed HIV-positive patients in Huzhou between 2017 and 2022. Pairwise genetic distances between sequences were calculated using HIV Trace based on the Tamura-Nei 93 method. The transmission network was constructed using Cytoscape v3.9.1. The effective reproductive number (Re) of each large cluster was estimated using the birth-death skyline model in BEAST v2.4.2. Multivariate logistic regression was performed to identify factors associated with clustering using R v4.4.3 software.

RESULTS

A total of 931 HIV pol sequences were successfully obtained, of which CRF07_BC (51.7%, 481/931) and CRF01_AE (27.5%, 256/931) were the predominant subtypes. The proportion of CRF07_BC increased from 43.5% in 2017 to 59.8% in 2022, whereas that of CRF01_AE decreased from 33.3% in 2017 to 19.5% in 2022. In total, 448 individuals formed 110 putative transmission networks with a clustering rate of 48.1%, ranging from 2 to 83 sequences per network. Four large clusters were identified, with a higher proportion of individuals aged ≥ 50 years (49.0%) compared to that in small/ medium clusters (35.5%) and non-clustered cases (26.1%). Multivariable logistic regression showed that clustering was associated with age ≥ 50 years (adjusted odds ratio [aOR] = 2.125, 95% confidence interval [CI]: 1.251-3.632), registered households in Huzhou (aOR: 1.677, 95% CI: 1.252-2.249), and CRF07_BC subtype (aOR: 2.119, 95% CI: 1.542-2.924). Only one of the four large transmission clusters had a Re > 1, with a high proportion (63.0%, 29/46) of male older adults exposed through commercial sexual contact.

CONCLUSIONS

The subtype of CRF07_BC was the predominant subtype locally, showing an increasing trend over time. Molecular transmission network analysis and multivariate logistic regression revealed that older adults play a key role in local HIV-1 transmission. Public health services should target this key population to curb the spread of HIV-1.