APPLICATION OF ESTIMATION AND PROJECTION PACKAGE TO THE CONTEXT OF AUSTRALIA'S HIV EPIDEMIC

Purpose: The Joint United Nations Programme on AIDS (UNAIDS) Estimation and Projection Package (EPP) released in late 2001 is a tool to assist national programs for use in making national estimates and short-term projections of HIV epidemic in respective countries. Transmission of HIV in Australia is primarily through sexual contact between men, and relatively small number of cases, are attributed to injecting drug use or to heterosexual contact. Our objectives were to derive current best HIV estimates using the UNAIDS EPP and assumptions that reflect the current understanding of HIV epidemiology in Australia, and to project estimates over the period 1975-2015.

Method: Australian surveillance and other pertinent data were used, with application of appropriate adjustment and calibration procedures. The input data include population size estimates, HIV seroprevalence data, and antiretroviral therapy (ART) data for men who have sex with men (MSM), injecting drug users (IDUs), and low-risk populations. The epidemic curves for each of the sub-epidemics generated by EPP were then combined with ART data into a demographic projection model, Spectrum to determine the consequences of Australia’s HIV epidemic.

Result: The EPP estimated that there would be 20,896 people living with HIV infection, 560 new HIV infections, 474 annual number of AIDS-related deaths, and 15,390 people needed for ART if eligibility for treatment remains at CD4 count <200 in Australia in 2010. The estimated HIV prevalence was 0.13% with a range of 0.08% to 0.2%. The EPP projected that the number of new HIV infections peaked between 1987-1990 at approximately 2,800, followed by a substantial decline until 1996-1997, then a small peak between 1997-1998 at ~1,000 infections and has remained relatively stable at between 550-560 since 2001 until 2015.

Conclusion: Our findings suggest that although the overall HIV prevalence is consistent with independent estimates and previous back-projection modeling estimates, EPP and Spectrum are not ideal for utilizing Australia’s strong HIV surveillance system and data. HIV in Australia is predominantly confined to MSM population. Also, due to effective community engagement the most-at-risk populations test for HIV at a relatively very high frequency. Thus, our HIV surveillance is predominantly based on accurate reporting of the number of HIV diagnoses, which we believe very closely mirrors actual incidence, and not on serial cross-sectional prevalence estimates for informing EPP.