Based on these assumptions, two submodels were constructed that are mathematically connected to form the combined ‘progression rate distribution’. The HIV incidence curve was then reconstructed by combining two back-projection estimated HIV incidence curves from AIDS diagnostic data (up to 1994, prior to which effective antiretroviral treatment was not available) and HIV diagnostic data using the combined progression rate distribution. The methodology also used the back-calculated HIV incidence to forecast what the trend of AIDS diagnoses over the years would have been in the absence of treatments. This forecast can be compared with the actual trend of AIDS

diagnoses from surveillance data. Details of this methodology are given in the Appendix A. User-friendly software for this methodology, written in the R language, PD0325901 in vitro together with other technical and methodological documents, is available upon request ([email protected]). Following a long-term decline, buy HM781-36B the annual number of new HIV diagnoses has gradually increased recently, from 763 cases in 2000 to 998

in 2006. Among the cases of newly diagnosed HIV infection, an increasing number were in people who had acquired HIV infection within the previous year. Summary figures suggest that, by the end of 2006, 26 267 diagnoses of HIV infection, 10 125 diagnoses of AIDS and 6723 deaths following AIDS occurred in Australia [5]. Table 1 shows the distribution of HIV diagnoses for three exposure categories. Estimated HIV incidence curves and their pointwise 95% confidence intervals (CIs), which were calculated by bootstrap [7], are plotted many for the three main routes of transmission (MSM, IDU and heterosexual acquired – for both men and women) in Fig. 1a–d. Model-predicted HIV and AIDS diagnoses (in the absence of therapies) along with their observed counts are also presented in Figs 2a–d and 3a–d, respectively. In recent years there has been a noticeable increase in the number of HIV diagnoses in MSM (Fig. 2a). The back-projection analyses suggest a peak HIV incidence in MSM of over 2000 new infections per year in the early 1980s, followed by

a rapid decline to a low of a little under 500 new infections per year in the early 1990s (Fig. 1a). It is estimated that the incidence of HIV infection then increased gradually through the early 2000s, to ∼750 new HIV infections in 2006. This is in broad agreement with previous reports and conventional back-projection estimates [8]. Our results also show that, to the end of 2006, a total of 19 689 men were infected with HIV through male homosexual sex, of whom 13% (95% CI 12%, 14%) are estimated not to have been diagnosed with HIV infection (Table 2). In 1997–2006, approximately 4% of HIV diagnoses in Australia were in people who reported a history of IDU (Annual Surveillance Report, 2007). The prevalence of HIV infection among people attending needle and syringe programmes remained low (∼1% in 2002–2006).