The evolutionary and transmission characteristic of HIV-1 CRF07_BC in Nanjing, Jiangsu.

To understand the epidemiology, evolutionary and transmission characteristics of HIV-1 CRF07_BC in Nanjing, China. One hundred and fifty-nine patients with HIV-1 CRF07_BC were recruited. DNA sequencing, phylogenetic analysis, and molecular transmission cluster analysis were conducted to determine the molecular epidemiology and evolutionary characteristics. Of these HIV-1-infected patients, 95.6% were male, and men who sex with men (76.7%) were the main transmission route. Only 34.0% of these cases were born in Nanjing, and most of them (64.8%) reported having multiple sex partners in the last 6 months. The maximum likelihood phylogenetic analyses of HIV-1 CRF07_BC revealed two lineages. Overall, 67.3% of Nanjing sequences were connected to at least one other individual distributed in 11 clusters, and the average degree was 21.2 with range (1-178). The clustered patients were more likely to be male. The time to a most recent common ancestor for the early HIV-1 CRF07_BC circulating in Nanjing was estimated to be 1998.71[1997.36-2001.07]. The mean estimated evolutionary rate for the epidemic cluster was slightly lower at 2.38[2.12-2.65]  ×  10-3 per site per year with the relaxed exponential clock model. HIV-1 CRF07_BC was transmitted into Nanjing more than 20 years ago from Yunnan and has become one of the most predominant subtypes with a higher evolutionary rate than before.