curves accessed from the AIDSinfo Online Database from the 2012 and 2013 UNAIDS reports, only differing by one more years of data, several countries showed considerable difference between the two incidence curves. In many cases estimated peak incidence was higher from the 2013 report (12 out of 19 countries had higher incidence peaks using the 2013 report data; median difference between highest incidence from 2013 to 2012 report among these 12 countries, 0.33, but as high as 1.37) sometimes occurring in a different year than the 2012 report, and these changes were evident as far back as 1990 (Annex 2).

Still, changes in incidence, estimated by Spectrum, have been important for measuring progress in the global fight against HIV/AIDS at regional and country levels. The 2012 Global AIDS report grouped countries by overall changes in incidence between 20012011, with those falling into categories of increasing incidence over 25%, stable incidence (less than 25% change in incidence, up or down), and those with reductions in incidence greater than 25% and 50%. Although the majority of countries in the 2012 report have estimated incidence reductions over 25%, a third of them are estimated to have experienced stable incidence, or worse, incidence increases over 25% between 2001 and 2011 (including Congo, Lesotho, Nigeria, Tanzania, and Lesotho, which have all experienced stable incidence over that period).

# **<u>2.2. Effect of ART on prevalence data, mortality, and infectiousness</u>**

Achieving universal access to ART (reaching 80% of those in need of treatment) is a global priority, and the provision of ARVs is a key component of combination HIV prevention strategies, as ART reduces the likelihood of both sexual and mother-to-child transmission of HIV. Following the hallmark HPTN052 study showing that early HIV treatment of HIV positive partners among sero-discordant couples significantly reduced transmission to their partners (Cohen et al. 2011), there has been a push in the global community for using HIV treatment as prevention on a population level ('Treatment as prevention for HIV' 2011). As progress towards achieving universal access is made (global ART coverage was estimated at 65% in 2012), the effects of ART on national HIV epidemics and measurements of it will increasingly become more prominent.

HIV prevalence is determined by HIV incidence and mortality, and the availability of ART makes inferring incidence from prevalence – in the absence of good mortality data - more challenging. As already mentioned, ART also influences fertility patterns, and the tracking of ANC trends is complicated by the effects of ART and declining HIV incidence on the age-distribution of HIV prevalence, shifting it towards less fertile age-groups. Another factor to be considered is the influence of ART patient demographics, for instance on Spectrum projected incidence. HIV incidence is commonly estimated for the adult population 15-49, but not all patients on ART are within this demographic (10-20% of ART patients are already over 50, and this percentage will increase as the ART patient cohort ages. This factor affected the 2012 UNAIDS estimates, and this assumption was 18