Drug Resistance After Failure of WHO Recommended First-Line Antiretroviral Regimen for Adult HIV-1 Infection in South Africa: A Modeling Analysis

BACKGROUND: Antiretroviral therapy (ART) is critical for ending the HIV epidemic. Tenofovir-containing ART is the first-line regimen in many countries including South Africa, with limited access to second-line ART. High levels of drug resistance have been reported among patients after virologic failure on tenofovir-containing first-line regimens (TenoRes Study, Lancet Infect Dis 2016). We assessed drug resistance at the population level using mathematical modeling. METHODS: We developed a stochastic individual-based model of the heterosexual HIV epidemic in KwaZulu-Natal South Africa, and compared drug resistance from scenarios of tenofovir-containing ART scale-up, either CD4-based (threshold < 500 cells/mL) or Fast-track (80% coverage by 2020). The model represents details of HIV transmission and disease progression, demography, sexual behavior, condom use, circumcision, treatment interventions and drug resistance dynamics including key mutations (M184V, K65R and non-nucleoside reverse transcriptase inhibitor (NNRTI)). Using an initial population of 2.5 million, we performed 100 simulations from 1978 to 2030. We examined the prevalence of (majority) transmitted and acquired resistance by 2030. RESULTS: The total resistance (proportion of HIV-infected persons with drug resistance) reached 34% from CD4-based ART by 2030, with 30% relative contribution from transmitted resistance and 70% from acquired resistance. In contrast, Fast-track ART reduced the total resistance to 22%; though, there was an increased relative contribution from transmitted resistance (~ 50%). In both scenarios, NNRTI mutations were the most prevalent, followed by M184V and K65R mutations. About 48% of persons with acquired drug- resistance harbored dual drug mutations, 44.7% had triple mutations and 7.3% just single mutations, from CD4-based ART. The respective estimates from Fast-track ART were similar; 49% for dual, 44.1% for triple and 6.9% for single mutations. In both scenarios, NNRTI mutations comprised about 80% of prevalent transmitted resistance. CONCLUSION: Current WHO-recommended first-line ART could lead to substantial drug resistance. Effective surveillance for resistance transmission and access to second-line regimens would be crucial. DISCLOSURES: All authors: No reported disclosures.