Adherence to therapy is a key factor in preventing the development of drug-resistant strains of HIV. Studies with currently available drugs have shown that adherence rates must be very high in order to achieve suppression of viral replication. In one study, more than half of the patients who took less than 95 percent of their ART doses had detectable viral loads, indicating active viral replication during the study period; many other studies have shown similar results.^3–8 While newer drugs with lower pill burdens and improved pharmacokinetics may lessen the need for near-perfect adherence, the currently available data highlights the importance of stringent adherence to ART.

There is no evidence to suggest that the emerging burden of viral resistance to ART will be worse in developing countries than in wealthier countries, and such concerns should not be used as arguments against providing life-saving therapy to those who need it. Rather, concerns regarding the emergence of viral resistance should encourage HIV programs to develop comprehensive strategies for the delivery of care. Every HIV treatment program should evaluate patient adherence to their regimens and determine strategies to enable and improve adherence, as discussed in Section 3.10. As ART becomes widely available, the WHO and its partners intend to collect reliable, updated information on the prevalence of drug-resistant strains among treated and untreated subjects.⁹