The advent in 1996 of potent combination antiretroviral therapy (ART), sometimes called HAART (highly active antiretroviral therapy) or cART (effective combination antiretroviral therapy), changed the course of the HIV epidemic.1 These "cocktails" of three or more antiretroviral drugs (ARVs) used in combination gave patients and scientists new hope fighting the epidemic,2 and have significantly improved life expectancy -- to decades rather than months.1,3
For many years, scientists believed that treating HIV-infected persons also significantly reduced their risk of transmitting the infection to sexual and drug-using partners who did not have the virus. The circumstantial evidence was substantial, but no one had conducted a randomized clinical trial -- the gold standard for proving an intervention works. That changed in 2011 with the publication of the findings from the HIV Prevention Trials Network (HPTN) 052 study, a randomized clinical trial designed in part to evaluate whether the early initiation of ART can prevent the sexual transmission of HIV among couples in which one partner is HIV-infected and the other is not. This landmark study validated that early HIV treatment has a profound prevention benefit: results showed that the risk of transmitting HIV to an uninfected partner was reduced by 96%.4
As a concept and a strategy, treating HIV-infected persons to improve their health and to reduce the risk of onward transmission -- also known as treatment as prevention -- refers to the personal and public health benefits of using ART to continuously suppress HIV viral load in the blood and genital fluids, which decreases the risk of transmitting the virus to others. The practice has been used since the mid-1990's to prevent mother-to-child, or perinatal, transmission of the virus. Research published in 1994 showed that zidovudine, more commonly known as AZT, when given to HIV-infected pregnant women and to their newborns reduced the risk of perinatal transmission from about 25% to 8%.5 Since then, routinely testing pregnant women and treating infected mothers with ART during pregnancy, delivery, and while breastfeeding, when practiced according to recommendations, has reduced the mother's risk of transmitting HIV to her child by 90%.6 In one study, women who received at least 14 days of ART reduced the risk of transmitting HIV to their babies to less than 1%.7
Putting Treatment as Prevention in Perspective
By itself, treatment as prevention is not going to solve the global HIV epidemic. On the domestic front, controlling and ultimately ending the epidemic will require a combination of scientifically proven HIV prevention tools as highlighted in the National HIV/AIDS Strategy, including
- Focusing on science-based HIV prevention efforts by supporting and expanding targeted use of high-impact HIV prevention approaches.
- Making better investments by intensifying HIV prevention in the communities where HIV is most heavily concentrated.
- Increasing access to HIV screening and medical care, including through
- boosting federal investments for AIDS Drug Assistance Programs (ADAPs) to expand access to life-saving medications, and
- implementing the Affordable Care Act, which will increase health coverage for thousands of Americans living with HIV.
- Sustaining a shared response to the domestic epidemic through the support of HIV prevention efforts across all levels of society, including federal, state, and local governments, faith-based communities, and the private sector.
Providing treatment to people living with HIV infection to improve their health must always be the first priority. Getting an HIV test is the first step to identifying persons with HIV infection and the pivotal entry point into the medical care system for both treatment and prevention. More than 1.1 million persons in the United States are living with HIV, and almost 1 in 5 (18.1%) do not know they are infected.8 By lowering the level of virus in the body, early ART helps people with HIV live longer, healthier lives and also lowers their chances of transmitting HIV to others. Although observational data had suggested that ART significantly reduces viral load and the risk of sexual transmission of HIV in heterosexual couples where one partner is infected and the other is not,9,10 it was the HPTN 052 study that definitively showed that early treatment of HIV-infected persons dramatically cuts the rate of new infections. Studies of communities with high concentrations of injection drug users (IDUs) and men who have sex with men (MSM) have shown that as ART use increased within the community, the community's viral load declined as did rates of new HIV diagnoses.11,12 However, it is critical to remember that the prevention benefit of treatment is not 100%, and at least one instance of HIV transmission from a person with suppressed viral load to an uninfected sexual partner has been reported.13
For persons living with or at risk for HIV infection, emphasizing these fundamental safeguards will continue to be crucial:
- knowing their HIV status through routine testing;
- getting into care soon after HIV diagnosis and starting antiretroviral treatment;
- remaining in care and staying on HIV treatment; and
- modifying behaviors that reduce the probability of getting or spreading HIV -- such as using condoms properly and consistently, reducing numbers of partners, and avoiding sharing needles and syringes.
Test and Treat
The ability of antiretroviral drugs to prevent secondary transmission of HIV from an infected person to an uninfected sexual or drug-using partner has led to several proposed "test-and-treat" strategies. Test-and-treat programs are based on the premise that the rate of new HIV infections will be maximally reduced by using aggressive methods to test and diagnose all people living with HIV infection, treat them with ART regardless of CD4 cell count or viral load at diagnosis, and link them to care. In one study, mathematical modeling suggested that a universal test-and-treat-strategy in which all adults aged 15 years or older are tested annually could control the South African epidemic, reducing both HIV incidence and mortality to less than one case per 1,000 people per year within 10 years of full implementation of the strategy -- and reducing prevalence of HIV infection to less than 1% within 50 years.14 Other investigators have not been as optimistic about the ultimate benefits of this strategy. Only 50% of persons in the United States with HIV remain in care,15,16 and about 18% do not know they are infected; these persons may contribute to the onward transmission of HIV. In addition to expanding testing and treating HIV infection earlier, overcoming the challenges of undiagnosed infection and poor engagement in care will result in better care of HIV-infected populations and reduced numbers of new HIV infections.17,18