Spatiotemporal Origin and Cross-Regional Transmission Dynamics of HIV-1 Circulating Recombinant Form (CRF85_BC) in Developed Eastern China: A Seven-Year Comprehensive Molecular Surveillance Study - Report - MDSpire
Clinical Report: Geographic and Temporal Origins and Spread of HIV-1 CRF85_BC
Overview
This retrospective, population-based study used seven years of HIV-1 molecular surveillance in Zhejiang, China (2017–2023), to investigate CRF85_BC introduction and spread. Analysis of 259 cases supported repeated introductions from southwestern China followed by sustained local transmission centered on Jiaxing. By 2023, CRF85_BC had reached all 11 prefecture-level cities and become the province’s fifth most prevalent HIV-1 subtype.
Background
HIV-1 genetic diversity is shaped by mutation and recombination. China’s B/C recombinant forms, including CRF07_BC and CRF08_BC, have spread beyond their initial populations and regions. CRF85_BC was formally designated in Sichuan in 2016; earlier investigations described local circulation in southwestern China. Zhejiang’s substantial cross-provincial migration and prefecture-level molecular surveillance provided a setting to examine its establishment outside that endemic area.
Objective
Investigate when and from where CRF85_BC entered Zhejiang, whether sustained local transmission occurred, and which geographic hubs and populations were involved in onward spread.
Approach
The study included 259 newly diagnosed individuals with confirmed CRF85_BC infection, complete core epidemiological information, and qualifying HIV-1 pol sequences. Phylogenetic analysis, Bayesian phylogeography, and molecular transmission networks were integrated to assess origins, dissemination, and clustering. Factors associated with clustering were evaluated using univariable and multivariable logistic regression.
Data Highlights
Measure or context
Reported information
Surveillance period
2017–2023 (seven consecutive years)
Surveillance setting
Province-wide HIV-1 molecular surveillance in Zhejiang, organized at the prefecture level
First reported Zhejiang detection
CRF85_BC was identified in Jiaxing during the 2017 prefecture-level surveillance pilot
CRF85_BC designation
Formally designated in Sichuan Province in 2016; described as a B/C recombinant with breakpoints across pol and env
Global HIV estimates cited in context
In 2024, 40.8 million people were living with HIV and 1.3 million new infections were reported worldwide
China migration context
The 2020 census identified Zhejiang as having the second-largest inflow of cross-provincial migrants among China’s provinces
Key Findings
CRF85_BC was detected in Zhejiang in 2017 and had reached all 11 prefecture-level cities by 2023.
Among 259 cases, 181 (69.88%) were male, 191 (73.75%) were aged 50 years or older, and 241 (93.05%) reported heterosexual transmission.
Phylogeographic analysis indicated multiple introductions from Sichuan and Yunnan, followed by transmission within Zhejiang centered on Jiaxing.
At a genetic distance threshold of 0.008 substitutions per site, 183 individuals (70.66%) formed 41 molecular clusters, including four large clusters.
Jiaxing accounted for 48.63% of clustered cases; 58.60% of genetic linkages connected two Jiaxing cases.
Adults aged 60 years or older had higher clustering before adjustment, but age was not independently associated with clustering afterward. Nonlocal household registration remained associated with lower clustering odds.
Across the four large clusters, posterior median effective reproduction numbers ranged from 0.45 to 2.68 over the modeled intervals. Although medians exceeded one in 24 of 40 intervals, the 95% credible intervals were wide and included one.
Interpretation
The findings support repeated introductions followed by local establishment, with Jiaxing acting as a principal hub. Higher clustering among older adults should be interpreted alongside residence and other population characteristics. The observed clustering rate does not establish greater intrinsic viral transmissibility.
Clinical Implications
The authors recommend routine provincial molecular surveillance, cross-provincial monitoring, and interventions focused on core clusters. Several large-cluster members had detectable viremia despite recorded antiretroviral therapy. The authors therefore recommend strengthening treatment management to maintain viral suppression, alongside targeted partner notification and promotion of preexposure prophylaxis.
Limitations
Analysis was restricted to the pol region rather than full-length genomes.
Undiagnosed infections and sequencing failures may have introduced selection bias and underestimated transmission linkages.
Individual-level behavioral survey data were unavailable, limiting differentiation of heterosexual transmission risks.
Differences in sampling and network thresholds prevented direct interpretation of clustering differences between regions as differences in intrinsic transmissibility.
Conclusion
CRF85_BC became established across Zhejiang following repeated introductions from southwestern China. The findings support molecular surveillance and coordinated prevention focused on affected populations and core transmission clusters.
Related Resources & Content
Spatiotemporal origin and cross-regional transmission dynamics of HIV-1 circulating recombinant form (CRF85_BC) in developed eastern China: a 7-year comprehensive molecular surveillance study — Qin Fan, Jiafeng Zhang, Jun Jiang, et al. — International Journal of Infectious Diseases. 2026;173:109207. doi:10.1016/j.ijid.2026.109207.
Identification of a novel HIV-1 circulating recombinant form (CRF85_BC) in Sichuan, China — Su L, Wei D, Yang H, et al. — AIDS Research and Human Retroviruses. 2016;32(9):895–899. doi:10.1089/aid.2016.0053.
Rapid circulation of HIV-1 CRF85_BC in Southwest China: its geographic origins and molecular transmission networks analysis — Liu Y, Yang C, Chang W, et al. — Frontiers in Cellular and Infection Microbiology. 2025;15:1624996. doi:10.3389/fcimb.2025.1624996.
