1364 AIDS RESEARCH AND HUMAN RETROVIRUSES Volume 20, Number 12, 2004, pp. 1364–1367 © Mary Ann Liebert, Inc. Sequence Note The Molecular Epidemiology of HIV Type 1 among Vietnamese Australian Injecting Drug Users in Melbourne, Australia CLAIRE E. RYAN, 1 JULIAN H. ELLIOTT, 2 TRACEY MIDDLETON, 3 ANNE M. MIJCH, 4 ALAN C. STREET, 2 MARGARET HELLARD, 1 NICK CROFTS, 1 SUZANNE M. CROWE, 1 and ROBERT B. OELRICHS 1 ABSTRACT The proportion of human immunodeficiency virus type 1 (HIV-1) among Vietnamese injecting drug users (IDUs) in Melbourne, Australia exceeds that of the background population. To investigate the molecular epi- demiology of HIV-1 among this group, the C2-V4 region of the HIV-1 envelope was directly sequenced from 11 Vietnamese Australians and 19 non-Vietnamese Australian controls. A significant difference in the distri- bution of the HIV-1 subtypes was demonstrated, with greater than 50% of Vietnamese Australian IDU shown to be infected with CRF01_AE—the predominant subtype in Southeast Asia, rather than subtype B, which dominates the Australian epidemic and which was found in 89.5% of the non-Vietnamese controls. The ge- netic diversity of the CRF01_AE epidemic in Vietnamese Australian IDUs was substantially lower that that of the background subtype B, consistent with a more recent introduction of a limited number of viral strains from Vietnam. These results support public health policy targeting Australian IDUs of Vietnamese ethnicity as a distinct vulnerable population. A LTHOUGH AUSTRALIA HAS BEEN SUCCESSFUL in maintaining a low prevalence of human immunodeficiency virus type 1 (HIV-1) among its population of injecting drug users (IDUs), there is concern about specific subgroups of injectors being at greater risk of infection. The proportion of Vietnamese Aus- tralian IDUs infected with HIV in Victoria is high compared with other IDUs; since 1996 there have been 38 reports of IDU- associated HIV-1 infection in Victoria and 11 of these 38 (29%) reported their country of birth as Vietnam. 1 Previous studies have reported that Vietnamese Australian IDUs are a relatively marginalized group who are less likely to access harm reduc- tion campaigns and are thus at heightened risk of HIV-1 in- fection. 2–4 Furthermore, other reports have suggested that this population has an additional, unique risk factor for HIV-1 ac- quisition—travel to Vietnam, a country where IDU carries a notable risk of HIV-1 infection. 2,4–6 The principal subtypes of HIV-1 in Australia and Vietnam differ. In Australia, subtype B predominates in all risk cate- gories 7,8 whereas the recombinant form CRF01_AE is ac- countable for the majority of infections among IDUs and com- mercial sex workers (CSWs) in the expanding Vietnamese epidemic. 9–13 This investigation aimed to further characterize the HIV epidemic occurring among Vietnamese IDUs in Aus- tralia at a molecular level and to determine whether travel back to Vietnam could be considered a significant risk factor for HIV-1 acquisition. 1 The Macfarlane Burnet Institute for Medical Research and Public Health, Prahran, Victoria, Australia. 2 Victorian Infectious Diseases Service, Royal Melbourne Hospital, Parkville, Victoria, Australia. 3 Victorian Infectious Diseases Reference Laboratory, Melbourne, Victoria, Australia. 4 Victorian HIV Service, The Alfred Hospital, Prahran, Victoria, Australia.