Use of HIV viral-load suppression to estimate the effect of community-wide home-based HIV counselling and testing and linkage to antiretroviral therapy on HIV incidence in South Africa: a mathematical modelling analysis

Abstract

BackgroundHigh coverage of HIV counselling and testing (HCT) through community campaigns, which link most HIV-positive people to care, has the potential to decrease HIV incidence if most eligible people initiate antiretroviral therapy (ART) and are virally suppressed. The aim of our analysis was to use transmission models of HIV to estimate the effect of home-based HCT on HIV incidence in South Africa. MethodsWe did an observational cohort study of community-wide home-based HCT in KwaZulu-Natal, South Africa, from September, 2011 to May, 2013. Resident adults within a geographically defined community were offered HCT. HIV-positive people received point-of-care CD4 cell count results, counselling about HIV and ART, referral for HIV care, and follow-up visits at months 1, 3, 6, 9, and 12. We assessed risk behaviour and adherence for HIV-positive people on ART. HIV viral load was measured among all HIV-positive people at baseline, 6 months, and 12 months. Using baseline HCT data and estimates from the literature, we developed a compartmental, deterministic model of HIV incidence in KwaZulu-Natal, incorporating sexual behaviour and ART use. The model population was stratified by sex, age, sexual activity, circumcision status, and condom use. We assumed that viral suppression on ART decreases HIV transmission by 90%, ART dropout was 5% annually, and the transmission probability in acute HIV was 26-fold higher than in chronic infection. Model output for HIV prevalence and incidence was validated with independent HIV survey data. We modelled the effect of home-based HCT every 5 years on HIV incidence at 5, 10, and 20 years. FindingsOf 1296 adults, 1273 (98%) were tested for HIV, of whom 404 (32%) were positive. At baseline, 158 (39%) participants were on ART and 127 (32%) were eligible for ART according to national guidelines (CD4 count ≤350 cells per μL). The median CD4 cell count among ART-naive individuals was high (472 cells per μL). By month 6, 359 (88%) participants of the HIV-positive group identified at baseline had visited an HIV clinic, and by month 12, 111 had initiated ART. At month 12, HIV viral load was suppressed among 233 (58%) of all HIV-positive people and among 170 (71%) of HIV-positive people on ART (n=241). With use of the proportion of all HIV-positive participants with viral suppression to indicate ART coverage and adherence, modelling estimated that: HCT every 5 years with ART initiated at CD4 count of 350 cells per μL or less would decrease HIV incidence over 5, 10, and 20 years by 31·3%, 32·9%, and 33·1%, respectively; and ART initiation at the new WHO guideline level of CD4 count of 500 cells per μL or fewer would decrease incidence by 41·0%, 44·6%, and 45·3%, respectively. With each round of HCT (assuming ART initiation at CD4 count ≤350 cells per μL), the proportion of incident cases from acute infection increased from 26% to 31%, 37%, and 40% over 5, 10, and 20 years, respectively. InterpretationAchievable rates of HCT to ensure community-wide HIV testing and ART initiation at levels recommended by current South African guidelines could substantially decrease HIV incidence, if the majority of HIV-positive people achieve viral suppression. The effect will be limited by transmission from acutely infected, untreated individuals who are highly infectious. FundingWe acknowledge the support of the NIH Directors Award, RC4 AI092552.