Characterizing trends in HIV infection among men who have sex with men in Australia by birth cohorts: results from a modified back‐projection method

Abstract

BackgroundWe set out to estimate historical trends in HIV incidence in Australian men who have sex with men with respect to age at infection and birth cohort.MethodsA modified back-projection technique is applied to data from the HIV/AIDS Surveillance System in Australia, including "newly diagnosed HIV infections", "newly acquired HIV infections" and "AIDS diagnoses", to estimate trends in HIV incidence over both calendar time and age at infection.ResultsOur results demonstrate that since 2000, there has been an increase in new HIV infections in Australian men who have sex with men across all age groups. The estimated mean age at infection increased from ~35 years in 2000 to ~37 years in 2007. When the epidemic peaked in the mid 1980s, the majority of the infections (56%) occurred among men aged 30 years and younger; 30% occurred in ages 31 to 40 years; and only ~14% of them were attributed to the group who were older than 40 years of age. In 2007, the proportion of infections occurring in persons 40 years or older doubled to 31% compared to the mid 1980s, while the proportion of infections attributed to the group younger than 30 years of age decreased to 36%.ConclusionThe distribution of HIV incidence for birth cohorts by infection year suggests that the HIV epidemic continues to affect older homosexual men as much as, if not more than, younger men. The results are useful for evaluating the impact of the epidemic across successive birth cohorts and study trends among the age groups most at risk.

A Review of the Literature on Event-Level Substance Use and Sexual Risk Behavior Among Men Who Have Sex with Men

“…Although diagnoses among other groups have been stable or have declined since 2000 [2], the recent incidence estimates of the Centers for Disease Control and Prevention (CDC) show an increase in new HIV diagnoses among MSM beginning in the early 1990s. Similar trends among MSM have been shown in other countries [2][3][4][5][6]. A model based on annual HIV incidence data since the introduction of highly active antiretroviral therapy in 1995 predicted that among a cohort of HIV-negative MSM aged 18 today, 41% would be infected by the time they reached 40 years of age [7].…”

Using HIV Diagnostic Data to Estimate HIV Incidence: Method and Simulation

“…This paper provides a detailed description of the method used in Wand et al (2009) to characterize trends in HIV infection among men who have sex with men in Australia by birth cohorts. We formulate the conditional distribution of time-to-testing given being infected through a mixture distribution model and link it with the conditional distribution of time-since-infection given being tested through the ratio of the expected number of new HIV infections to the expected number of new HIV diagnoses.…”

Disproportionate Impact of Combination Antiretroviral Therapy on AIDS Incidence in Australia: Results from a Modified Back-projection Model

“…In Australia, the early and widespread introduction of harm reduction interventions for people who inject drugs, such as accessible Needle and Syringe Programs, have resulted in HIV remaining at low prevalence levels of 1% or less [23,24]. Although HIV incidence among IDUs is declining or remaining at low levels in Australia [13], trends in AIDS diagnoses have not decreased, particularly among the older group since the introduction of cART. This is consistent with lower CD4 counts at presentation with HIV infection in IDUs compared with MSM on average [12].…”

“…The mixture distribution model given by equation (4) results in an overall ''bath-tub'' shaped hazard [13]. This model was allowed to vary over time, so that the proportion of diagnoses due to clinical symptoms was assumed to decrease over time.…”

“…We previously estimated past and current trends in HIV incidence in Australia for selected populations categorized by exposures using a modified back-projection methodology [13,14]. Results indicated that recent increases in HIV diagnoses in MSM reflect an increasing trend in underlying HIV incidence over recent years.…”