Introduction Rates of new HIV diagnoses are increasing in Australia, with evidence of an increasing proportion of non-B subtypes reflecting a growing impact of sexual networks, migration and travel. This present study aims to further define HIV-1 subtype diversity and investigate HIV-1 transmission networks within Australia.

Methods The Australian Molecular Epidemiology Network (AMEN) HIV collaborating sites in Western Australia, South Australia, Victoria, Queensland and Western Sydney, provided baseline HIV-1 partial pol sequence, age and gender information for a total of 4929 patients during 2005–2012. HIV-1 phylogenetic analyses utilised MEGA V6, with a stringent classification of transmission clusters (bootstrap ≥98%, genetic distance ≤1.5%).

Results HIV-1 B subtype represented 74.9% of 4929 sequences (WA 59.3%, SA 68.6%, W Syd 75.2%, Vic 75.7%, Qld 82.3%), with a greater proportion of clusters compared to non-B subtypes (27.6% vs 22.4% of sequences, p = 0.003), larger cluster size (36.0% with >2 sequences vs 24.8% of non-B clusters, p = 0.03) and more male-only groups (90%). The largest cluster comprised 29 B subtype sequences from Vic + WA (age range 23–70 years). HIV-1 subtype C networks (38 groups) included more female/male groups (73.6%) and a smaller proportion of groups >2 (16%), while CRF01_AE networks (44 groups) included 59.1% male-only groups, with groups >2 accounting for 22.7%.

Conclusion This nationwide study of HIV-1 sequences involving 4929 patients’ highlights the increasing diversity of HIV-1 subtypes within the Australian epidemic, as well as differences in transmission networks within Australia that are associated with these HIV-1 subtypes. These findings provide epidemiological insights not readily available using standard surveillance methods and can inform the development of effective strategies for prevention of new HIV-1 diagnoses across Australian state boundaries.

Disclosure of interest statement None declared.