Econometrics: Panel Data Methods

Abstract

We investigated the current success of early HIV detection in Australia and the likely effectiveness of Treatment as Prevention. HIV diagnoses data from the Australian National HIV/AIDS Registry were analyzed for CD4 T-cell counts at diagnosis and for prior HIV testing. Mathematical modeling based on these data estimated future HIV prevalence and incidence under different scenarios of antiretroviral therapy (ART) usage. CD4 T-cell counts significantly decreased with age (P < 0.0001) for men who have sex with men (MSM) and women in all HIV diagnoses, and for diagnoses at primary HIV infection (P < 0.02). This decrease with age meant that >50% of MSM aged 29 years and older are diagnosed with a CD4 T-cell count <500 cells per cubic millimeters. Diagnosis during primary HIV infection has stabilized at 15% for MSM, with a lower percentage for older individuals (P = 0.002), but only 5% of women were diagnosed at this early stage. MSM older than 50 years were significantly less likely to have had an HIV test before diagnosis (P < 0.0001), whereas women of all ages at HIV diagnosis were less likely to have been tested than MSM. Mathematical modeling indicated that current levels of ART would see a continuing increase in HIV diagnoses among MSM. A 90% ART enrollment would result in an almost immediate decline in prevalence and would be cost effective in terms of person-years on ART by 2028. Treatment as Prevention would be an effective intervention in Australia and other developed countries.