These subgroup analyses are of particular importance in assessing the success of prevention programmes, and for the allocation of prevention resources. The coupling of the methodology used in this study with a long-established HIV/AIDS database created a unique opportunity to reconstruct the HIV infection curve. In Australia, HIV transmission is monitored through the notification of cases of newly diagnosed HIV infection, including cases with evidence of newly acquired HIV infection, which is defined as HIV infection with evidence of a prior negative test or a diagnosis of primary HIV infection or an indeterminate western

blot within 12 months of HIV diagnosis. Therefore, there are potentially three data sources available in each calendar year: HIV surveillance data (first HIV-positive diagnoses by year of BIBW2992 diagnosis), data on newly acquired HIV infections (recent infections among new HIV diagnoses) and AIDS case Crizotinib molecular weight reporting surveillance data (based on physicians’ reporting on diagnoses of clinical events subject to the AIDS case definition) [5]. The back-projection method was originally proposed by Brookmeyer and Gail and used in Western countries in the late 1980s and early 1990s to estimate trends in HIV infections based on reported AIDS diagnoses [1]. This methodology used data on reported AIDS cases, combined with an assumption of the rate at which Tryptophan synthase people progress

from HIV infection to AIDS diagnosis (the incubation period), to estimate the most likely pattern of past HIV incidence. The availability of effective antiretroviral therapies from 1997 onwards altered the distribution of the incubation period in ways that are difficult to quantify. As a result, application of the method to current AIDS diagnosis data is unlikely to give reliable estimates of HIV infection rates. Some researchers [6] have modified the incubation function to account for the treatment effect, but this approach has generally been unsuccessful because of the difficulty of capturing the complexity of treatment regimens

and their effects. Others [7] have incorporated HIV diagnosis data into the back-projection method to improve the reliability of estimation. The back-projection method that we used in this study differs from similar approaches in the literature, in that it does not require data linkage between the HIV and AIDS diagnostic registries. It is based on a parametric formulation of the time between the acquisition of HIV infection and the earliest diagnosis of HIV infection obtained from enhanced HIV surveillance systems or from laboratory-confirmed testing. For an infected individual, a diagnosis of HIV infection may be made as a consequence of an awareness of recent exposure, the onset of symptoms related to HIV disease progression, random detection or frequent testing.