Increasing HIV transmission through male homosexual and heterosexual contact in Australia: results from an extended back-projection approach.

OBJECTIVES

The aim of the study was to reconstruct the HIV epidemic in Australia for selected populations categorized by exposure route; namely, transmission among men who have sex with men (MSM), transmission among injecting drug users (IDUs), and transmission among heterosexual men and women in Australia.

DESIGN

Statistical back-projection techniques were extended to reconstruct the historical HIV infection curve using surveillance data. Methods We developed and used a novel modified back-projection modelling technique that makes maximal use of all available surveillance data sources in Australia, namely, (1) newly diagnosed HIV infections, (2) newly acquired HIV infections and (3) AIDS diagnoses.

RESULTS

The analyses suggest a peak HIV incidence in Australian MSM of approximately 2000 new infections per year in the late 1980s, followed by a rapid decline to a low of <500 in the early 1990s. We estimate that, by 2007, cumulatively approximately 20 000 MSM were infected with HIV, of whom 13% were not diagnosed with HIV infection. Similarly, a total of approximately 1050 and approximately 2600 individuals were infected through sharing needles and heterosexual contact, respectively, and in 12% and 23% of these individuals, respectively, the infection remained undetected.

DISCUSSION

Male homosexual contact accounts for the majority of new HIV infections in Australia. However, the transmission route distribution of new HIV infections has changed over time. The number of HIV infections is increasing substantially among MSM, increasing moderately in those infected via heterosexual exposure, and decreasing in IDUs.