The spread of HIV-1 subtypes B and CRF01_AE among injecting drug users in Bangkok, Thailand.

The HIV epidemic among injecting drug users (IDUs) in Bangkok was initially dominated by HIV subtype B and later by the recombinant CRF01_AE. The present study investigates the distribution of the 2 variants in time and how it is affected by changes in injecting risk behavior and treatment. A mathematic model describing the spread of HIV subtype B and CRF01_AE among IDUs was developed, and data from the AIDSVAX B/E cohort of IDUs in Bangkok were used. From the model, it was calculated that during 1999 to 2003, the annual incidence of HIV was around 0.6 and 2.7 to 3.9 infections per 100 person-years for subtype B and CRF01_AE, respectively. Of the new infections, 18% and 72% are first infections with subtype B and CRF01_AE, respectively, and 9% are superinfections. With increases in risk behavior, the fraction of superinfections rises. If treatment reduces the infectivity of CRF01_AE more than that of subtype B, the fraction of subtype B infections should increase. Subtype B should remain prevalent in a small but considerable fraction of the population for a long time. Changes in risk behavior and the introduction of treatment may alter the distribution of subtypes, but CRF01_AE should remain dominant.