Treatment as Prevention
Antiretroviral medication has been successfully used in a number of ways: first and foremost to treat those with high viral load and diminishing CD4 counts; secondly to prevent vertical transmission of HIV from pregnant and breastfeeding women to their infants; third, as a prophylactic for those who have been exposed to HIV occupationally or through sexual assault (post-exposure prophylaxis, PEP); and finally as pre-exposure prophylaxis (PreP). "ART can reduce HIV transmission both directly by reducing viremia and thereby HIV transmissibility and indirectly by reducing risk behavior among those diagnosed, counseled, and treated." (IOM, 2011: 37). Recently, a landmark study, HPTN 052, has shown that early initiation of antiretroviral therapy (when CD4 counts were between 350 and 550 before many would normally be eligible for treatment in most countries) for the seropositive partner in a discordant relationship resulted in a 96% relative risk reduction of HIV transmission to the seronegative sexual partner (Cohen et al., 2011b). While there are several contributing factors in this study [See Staying Healthy and Reducing Transmission], the results of this study have led many to recommend the use of treatment as a prevention strategy. In 2011, following the results of this study, the US Institute of Medicine recommended "giving priority to prevention as a central tenet of a sustainable long-term response to the HIV/AIDS epidemic... applying evidence-based public health approaches... [and] increasing access to and coverage of synergistic combinations of known effective prevention technologies" (IOM, 2011: 8 and 9).
Critical questions around treatment as prevention include which populations living with HIV have access to treatment. Even if all serodiscordant couples had access to treatment as prevention, this would still not end the epidemic. In the study by Cohen et al. 30% of HIV-positive spouses also had an outside partner (Cohen et al., 2011b; Celum, 2011). But modeling has shown that for some countries, high rates of serodiscordant partnerships with treatment of the serodiscordant partner could lead to a fairly large reduction in incidence with a substantial number of infections prevented (El-Sadr et al., 2011a). Thus the ethical and public health challenge is "how we choose to distribute a limited resource antiretroviral drugs for treatment, for prevention or for both" (Cates, 2011: 225).
When more people living with HIV are on treatment, incidence goes down. However, more methods are needed for detecting acute infection, as acute transmission has been shown to increase the risk of transmission (Powers et al., 2010 cited in Smith et al., 2011). No strategies, especially in resource-limited settings, have been developed to prevent transmission among those who are acutely infected and the use of antiretroviral therapy during acute infection, either for personal or public health benefit, is controversial (Cohen et al., 2012). In addition, those on treatment may reduce condom use (Hasse et al., 2010 cited in Smith et al., 2011), although results from different studies have been mixed. [See Staying Healthy and Reducing Transmission] "Challenges remain in defining the optimum strategy for using treatment as prevention, finding the most contagious people, and providing both personal and public health care" (Smith et al., 2011: 323).
While the biggest challenge is providing treatment to all who can benefit, another challenge for treatment as prevention is that some believe it may violate the rights of people living with HIV by rolling out treatment for a public health benefit for people living with HIV who have CD4 counts above 350 or even 500 who are asymptomatic rather than for the individual patients' benefit. In addition, concerns have been raised that treatment for prevention may lead to loss of follow-up, poor levels of adherence, and increase in the prevalence and transmission of drug-resistant strains of HIV (GNP+ and UNAIDS, 2011). If given treatment as prevention, the person with HIV must be fully informed and agree to the potential risks and benefits on her/his health (GNP+ and UNAIDS, 2011). Others have argued "treatment should first and foremost be used for therapeutic purposes," targeting those who are sickest, which would be "ethical, feasible and epidemiologically sound" (Wagner et al., 2010: 1). Other prominent scientists and treatment activists have agreed that treatment should be available to all in medical need (Ambrosioni et al., 2011). "Scientists and policymakers alike agree that infected people should receive the lifesaving drugs before the uninfected" (Cohen, 2011b: 1340). But treatment and prevention are synergistic and can work together to reduce the burden of the AIDS epidemic (AVAC, 2010). Or as Dr. Fauci, who heads U.S. National Institute of Allergy and Infectious Disease (NIAID) stated, "We should just forget about [the idea of the tension between treatment and prevention] and just put it behind us, because treatment is prevention" (Fauci cited in Cohen et al., 2011c: 1628). Yet, "the logistical requirements for successful use of ART for prevention are considerable" (Smith et al., 2011: 315), while at the same time serving as a cornerstone of combination prevention of HIV (Smith et al., 2011). Numerous questions and challenges remain to enact treatment as prevention in resource-limited settings (Zachariah et al., 2010); however, inaction would also be inexcusable. Some of the challenges include missing acute infections, long-term adherence, the possibilities of drug resistance, and the concerns that condom use and other preventive measures would decrease (Shelton, 2011a). A continued focus on all prevention modalities, including treatment is warranted (Nguyen et al., 2011).
Thus, although recent results "... support the use of antiretroviral treatment as a part of a public health strategy to reduce the spread of HIV-1 infection" (Cohen et al., 2011a: 501), "the burden of adding antiretroviral-based prevention to already strained health systems remains to be determined" (Padian et al., 2011b: 271). Yet global consensus has been reached that treatment can serve to prevent HIV acquisition, especially at CD4 counts under 350; treatment for those at CD4 counts under 350 must be scaled up and health systems must work to increase adherence and reduce loss to follow up (see treatment section).
Experts agree that HIV prevention must be prioritized as a "mainstay of a sustainable response" (AIDS2031 Consortium, 2010: xiii). Without substantial targeted HIV prevention efforts, new HIV infections will continue to outpace treatment efforts "even while recognizing some prevention effects from expanded treatment" (AIDS2031 Consortium, 2010: 24). For example, in Zambia, "nearly twice as many incident infections would occur in 2031 under a treatment-only approach as would occur with a combination of robust prevention and treatment efforts" (AIDS2031 Consortium, 2010: 25). "Failure to reduce incidence rates will make the goal of universal access to treatment impossible" (IOM, 2011: 60). Gender is key to testing and treatment. Globally, more women have been tested for HIV and more women have accessed antiretroviral therapy, with men facing numerous gender-related barriers to accessing testing and treatment, while women face gendered barriers to adherence. [See HIV Testing and Counseling for Womenand Treatment]
A fuller discussion of the role of treatment in reducing HIV transmission can be found in the treatment section.