At the end of 2008, after almost three decades since AIDS was first identified, neither a cure nor a fully preventive vaccine is available 
. Despite multiple efforts, the epidemic remains an exceptional challenge. It is estimated that, in 2008, 33 million individuals are living with HIV/AIDS in the world, 2.7 million (range 2.2–3.2million) became HIV infected and 2 million (range 1.8–2.3 million) died from AIDS-related causes 
. Despite substantial prevention efforts and increases in antiretroviral therapy roll-out programs, the epidemic continues its relentless pace. The ability to control HIV/AIDS morbidity and mortality, as well as the spread of HIV has been further compromised as a result of the worldwide financial crisis 
It is increasingly apparent that a targeted combination of proven effective interventions will be necessary if we are going to have a chance to control the impact of HIV/AIDS 
. Expanding access to antiretroviral treatment to those in medical need has been proposed as a key component of the above mentioned combination prevention approach 
. In brief, highly active antiretroviral therapy (HAART) decreases plasma HIV-1-RNA levels to undetectable levels of currently available assays (i.e. <50 copies/mL) in a sustained and reliable fashion. This leads to a dramatic decrease in HIV-1-RNA in sexual secretions (including semen, vaginal fluids and rectal mucosa), which in turn is associated with substantial decrease in the risk of HIV transmission. This effect has now been documented in mother-to-child transmission studies, as well as in observational studies involving discordant heterosexual couples and population-based cohorts 
. More recently, further supportive evidence derived from a longitudinal study of injection drug users was presented, where “community” HIV-1-RNA level was found to be the strongest predictor of HIV incidence even after adjusting for traditional risk factors including needle sharing and high-risk sex 
. Not surprisingly, “community” HIV-1-RNA level in this study was inversely correlated with the use of HAART.
HIV/AIDS related morbidity and mortality have decreased dramatically with the widespread availability of HAART 
. Today, HIV/AIDS is seen as a chronic and manageable condition with continued use of HAART, even in resource-limited settings as a result of the relentless roll-out of antiretroviral therapy 
. Sadly, however, access to HAART remains a challenge throughout the world, even within resource-rich regions 
. Egger et al. 
, using data from 42 resource-limited and resource-rich countries (total of 33008 individuals), has shown that in the vast majority of countries the median CD4 cell count at the time of initiation of HAART is substantially below 200 cells/mm3
. At such a level, the risk of disease progression or death is only partially reversed by HAART 
Even in British Columbia (BC), Canada, where there is a universal health care system that provides medical services, including laboratory monitoring, care and antiretroviral therapy free of cost, it has been shown that late or no access to care are major determinants of HIV/AIDS-related mortality 
. In BC, this tends to be particularly prevalent among rural and urban aboriginal populations, female sex-trade workers, street-involved youth, immigrants from HIV-endemic countries, younger men who have sex with men, as well as among the poor, the homeless and those with mental health and addiction challenges, also referred to as hard-to-reach population 
. Here and abroad, the health system has been slow to recognize that facilitated and supported access to care represents a cost-effective means of enhancing HIV/AIDS control, as it relates to HIV/AIDS-related morbidity and mortality as well as HIV transmission.
Recently, the International AIDS Society-USA (IAS-USA) updated the guidelines for the use of HAART in adults infected with HIV 
. In brief, the 2008 IAS-USA guidelines substantially expanded eligibility to HAART as it recommended that HAART should be offered to all symptomatic HIV infected individuals and to those who are asymptomatic but have CD4 cell counts below 350 cells/mm3. Furthermore, according to the 2008 IAS-USA guidelines, HAART should be offered to all asymptomatic individuals regardless of CD4 cell count if they are at high risk for short-term progression of their disease, as demonstrated by a plasma HIV-1-RNA level above 100,000 copies/mL or an absolute CD4 cell count decrease greater than 100 cells/mm3 within a year. Finally, for the first time based on the new understanding of HIV infection as a chronic inflammatory disease, the 2008 IAS-USA guidelines recommend that HAART should also be offered to all asymptomatic individuals regardless of CD4 cell count if they have an underlying condition or morbidity risk that will be aggravated by untreated HIV infection or that will compromise their future treatment options. Most prevalent among these are history of cardiovascular disease or increased cardiovascular risk, HIV-associated nephropathy, and chronic active hepatitis B or C. Similar recommendations have now been put forward in the USA and in Europe 
. Based on these guidelines changes, the number of individuals eligible for HAART has increased substantially. However, no estimates are available regarding the potential impact that the implementation of the 2008 IAS-USA guidelines might have on HIV/AIDS related morbidity and mortality and on HIV transmission in a given population.
Therefore, we undertook the present study to estimate the potential impact of the 2008 IAS-USA guidelines on HIV/AIDS related morbidity and mortality and HIV transmission in BC, via a deterministic mathematical model, in the next 5 (short-term) and 40 (long-term) years, under different HAART expansion scenarios.
We decided to focus on the impact of the new guidelines in BC, given that it houses the British Columbia Centre for Excellence in HIV/AIDS, which has been instrumental in the concept of HAART expansion as a powerful way to curb the HIV epidemic.