viruses in different islands. Another explanation is that there may be some form of consistant selection pressure on these viruses that is not as strong in subtype B viruses from the developed world. As mentioned earlier, the Caribbean is the only region of the world that has a robust heterosexually-driven epidemic of subtype B. In Thailand, South Africa and Argentina, concentrated epidemics in high risk populations preceded generalized epidemics in the general public. In each of these cases, subtype B was the subtype common in the concentrated epidemic and a non-B subtype replaced it as the epidemic grew [9,16]. Subtype B viruses from the Caribbean may have acquired features that have enabled it to generate a more ‘successful’ heterosexual epidemic. The data presented here have limitations: the samples used were not collected using any systematic sampling method and might not adequately represent the strains in these four countries. The number of full length genome sequences that could be performed was limited, and the selection of those was determined by ease of amplification, which could bring in a consistant bias against certain strains. These primers have been used successfully for many subtypes and the likelihood of sequence bias is not high, however. In general, the study was limited by the small sample size, and this would have been more consequential if the molecular epidemiology had been more complex. The findings, however, are References 1. UNAIDS, Caribbean, in 2006 AIDS Epidemic Update. (2006) Geneva, Switzerland: World Health Organization. 2. Inciardi JA, Syvertsen JL, Surratt HL (2005) HIV/AIDS in the Caribbean Basin. AIDS Care 17 Suppl: 1S9–25. 3. Wheeler VW, Radcliffe KW (1994) HIV infection in the Caribbean. Int J STD AIDS 5(2): 79–89. 4. UNAIDS, Caribbean, in 2007 AIDS Epidemic Update - Regional Summary. (2007) Geneva, Switzerland: World Health Organization. 5. 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