At least 7 HIV-1 subtypes (A, B/B', C, D, E, F, and G), and 3 major circulating recombinant forms (CRF01_AE, CRF07_BC, and CRF08_BC) have spread in China [28] [29] [30] [31] . However, the most prevalent HIV-1 strains are subtype B' (44%), C (29%, usually CRF08_BC) and CRF01_AE (13%) [30] . Subtype C and B'/B are the main subtypes among IDUs [30, 32] . Co-circulating of multiple subtypes of HIV-1 in China implies the possibility of interclade recombination. Characterization of genetic variability of HIV-1 may help track the epidemic, generate subtype-specific immunological reagents, develop vaccines, and choose antiretroviral therapy regimens.