Background: A new epidemic of HIV-1 among injection drug users (IDU) in Guangxi Province, China was first noted in 1996. 2 routes of the epidemic converge in Guangxi as documented by 2 circulating recombinant viruses, CRF08_BC from Yunnan and CRF01_AE from Vietnam. Previous studies on limited numbers have suggested striking homogeneity of viral sequences. In this study, samples from 106 HIV+ IDUs from 2 cities in geographically separate locations were assessed.

Methods: Heroine users were enrolled from 2 cities in Guangxi (Binyang, n= 329 and Pingxiang, n= 286), 80% of whom used intravenous drugs. Blood samples collected between September and October 2000 from 106 HIV-1-positive IDUs (Binyang, n= 62 and Pingxiang, n= 44) were tested for HIV-1 RNA levels by Roche Amplicor v1.5.  Of the 100 subjects with quantifiable RNA levels, 93 were further analyzed by extracting the equivalent of 6 mL of sera and amplifying pol gene (nt 1831-3025 of HXB2) by RT-PCR.  C2-V5 envelope sequence data are currently being generated.  For internal control 25% of the samples were re-amplified, sequenced, and analyzed in a blinded fashion.  Phylogenetic relationships were inferred using PHYLIP and inter-subject variation was quantified using Hamming distances.

Results: The incidence rates in these cities 9.5% and 5.3% per year for Binyang and Pingxiang for the year 2000, respectively. 100/106 subjects had quantifiable HIV-1 RNA levels with a median value of 2.2x10⁴ copies/mL. There were no significant differences in median HIV RNA level in Binyang (2.6x10⁴) and Pingxiang (2.2x10⁴). 72/93 samples were pol RT-PCR positive in a concentration dependant manner with 55%, 81%, and 100% of samples amplified with HIV-RNA titers of >10³, 10⁴, and 10⁵ copies/mL, respectively. 29/31 samples from Pingxiang were CRF01_AE with the remaining 2 being CRF08_BC.  39/41 samples from Binyang were CRF08_BC with the remaining 2 being a distinct new AE variant. There were no differences in viral load by genotype.  Median intersubject variation for the two CRF forms was 1.9% for CRF01_AE and 1.0% for CRF08_BC infected subjects.

Conclusions: The HIV-1 epidemic in Guangxi is dominated by distinct CRF01_AE coming through Vietnam and CRF08_BC coming through Yunnan.  These predominant subtypes have extraordinarily low inter-subject variation.   Finally with different incidence rates in these 2 cities, but with similar viral loads, CRF08_BC may be better adapted at parental transition than CRF01_AE.