Sustained Spread of HIV-1 CRF55_01B in Its Place of Initial Origin: Dynamics and Hotspots.

Background: Shenzhen, a city with a substantial mobile population, was identified as the first discovered region of HIV-1 CRF55_01B and epicenter of its severe epidemic. During the implementation of venue-based behavioral interventions and the "treat-all" policy, discerning the spread patterns and transmission hotspots of CRF55_01B is imperative.

Methods: In this study, 1,450 partial pol sequences, with demographic information, were collected from all newly diagnosed CRF55_01B infections in Shenzhen from 2008 to 2020. Molecular networks were constructed using the maximum likelihood and time-resolve phylogenies. Transmission rates, effective reproduction numbers (Re) of clusters and viral dispersal were evaluated using Bayesian inference.

Results: In total, 526 sequences formed 114 clusters, including seven large clusters. The status and size of clusters were strongly correlated with age, ethnicity, occupation and CD4+ T cell counts. The transmission rates of clusters were significantly higher than the national epidemic estimate. Four large clusters had Re exceeding 1 at the end of sampling period. Immigrants from Guangdong and Hunan, along with local residents, were identified as the transmission hubs, with heterosexual men being the main source and MSM being the main destination. The virus exhibited a high movement frequency from individuals aged 30-49 years toward diverse age groups.

Conclusions: This study demonstrated the hidden CRF55_01B transmissions continued despite current combined interventions in Shenzhen, and special at-risk individuals susceptible to infection or transmission were identified, potentially serving as targets for more effective prevention and control of the local epidemic, thereby mitigating cross-regional spread nationwide due to population migration.