were evaluated for 1) rising or falling curves and rates of change between 1990 and 2012, 2) how well empirical and modeled UNAIDS data match each other, and 3) dynamics before and during the ART scale-up period (2004 –2012).

Briefly, it was found that the countries analyzed experienced overall decreases in UNAIDS modeled incidence since 2000, with the exception of Burkina Faso, Burundi, and Uganda. Modeled incidence in these three countries has shown very little change, and in some cases, a slight upward trend through some years. There is great variation in the slope of downward trends across countries since 2004, with some having small and moderate declines (slope -0.01 to -0.06), and others with steeper and more dramatic declines (slope -0.08 to -0.14). Available antenatal sentinel surveillance and populationbased survey data in young females support these HIV trends, though the dynamics may slightly differ by rates of change and/or timing. In Nigeria, the Spectrum-estimated HIV incidence decline is not supported by the ANC-derived HIV prevalence in young females in the time period 2005-2010. Relatively few directly measured incidence data have been reported from HIV intervention trials or observational studies (we found 43 sources of measured incidence data from 10 of the selected countries); however, the reported HIV incidence levels tend to be higher than modelled national incidence estimates and are likely due to intentional targeting of high risk populations in research. We observed that modeled HIV incidence had begun to decline prior to ART scale-up, and in most cases where HIV data prior to 2004 were available, HIV prevalence trends in young females 15-24 supported this incidence decline prior to ART scale-up. This analysis, however, was not designed to assess the impact of the increasing coverage of ART on HIV incidence trends in the selected countries. Therefore, it is difficult to determine if or how much ART scale-up has contributed to incidence decline, though its effect cannot be ruled out, as recent data show that increased ART coverage reduces transmission risk in a South African hyperendemic HIV situation (Tanser et al. 2013). At the same time, new analyses from South Africa (Shisana et al. 2014) suggest no change in HIV incidence in two inter-survey periods stretching from 2005 to 2012, despite significant ART scale-up in that time period.

In conclusion, three main points can be taken from this analysis of HIV incidence trends in Sub-Saharan Africa: 1) Modeled HIV incidence and nationally reported HIV prevalence levels in young females suggest that national HIV incidence has declined since 2000 in all except three countries analyzed (stable estimated HIV trends in Burkina Faso, Burundi, and Uganda), but trial and survey data suggest that in some demographics, HIV incidence remains critically high; 2) All modelled national HIV incidence curves and most empirically observed trends commenced a downward trajectory prior to the introduction of ART programs around 2004, suggesting the contribution of other factors, such as HIV prevention programs and natural epidemic dynamics, to this decline; and 3) Modelled HIV incidence estimates including the incidence peaks in the past, exhibit much variation between Spectrum model versions and when new data is added, emphasizing the uncertainty of model outputs and the need to use incidence estimates with caution.

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