Population-level risk factors for vertical transmission of HIV in the national prevention of mother-to-child transmission programme in South Africa: An ecological analysis

Abstract

Background. Although South Africa has an overall mother-to-child transmission (MTCT) of HIV rate <5%, case rates remain high. Objectives. To identify population-level predictors of MTCT to inform targeted interventions to further reduce paediatric HIV incidence. Methods. The study was an ecological analysis of routine laboratory HIV-related test data from a synthetic cohort of women of reproductive age living with HIV (WRLHIV), identified from the National Health Laboratory Service’s Corporate Data Warehouse between 2016 and 2017. Criteria based on syphilis screening and timing of HIV-related tests were used to identify pregnant and non-pregnant WRLHIV. Pregnant WRLHIV were followed from cohort entry at the first antenatal care (fANC) visit, through delivery to exit at the latest viral load (VL) or 15 months post delivery. Follow-up for non-pregnant WRLHIV started at cohort entry on 1 January 2016 to exit at the latest VL or 31 December 2018. HIV VL tests performed at cohort entry, delivery and cohort exit described viraemia (VL ≥50 copies/mL) at subdistrict level. A negative binomial regression model determined the association between MTCT cases and the number of viraemic WRLHIV at different time points, controlling for number of WRLHIV aged <25 years at cohort entry and other routine HIV-related indicators at subdistrict level. Results. Of 3 386 507 WRLHIV identified, 178 319 (5.3%) met criteria for pregnancy. Median (interquartile range (IQR)) proportions of women with fANC booking <20 weeks’ gestation, maternal HIV seroprevalence during antenatal care (ANC) and antiretroviral therapy (ART) coverage during ANC were 68.2% (62.9 - 72.8), 31.5% (23.4 - 35.7) and 94.8% (89.7 - 97.8), respectively. Viraemia was consistently higher in pregnant v. non-pregnant WRLHIV at median proportions of 42.9% (38.3 - 59.3) v. 35.0% (25.9 - 49.0) at cohort entry (p<0.001) and 36.3% (25.0 - 48.4) v. 29.6% (21.0 - 42.6) at cohort exit (p<0.001). In total, 4 535 children aged <24 months tested HIV polymerase chain reaction-positive, representing a median subdistrict-level case rate of 1 372 (914 - 2 077) per 100 000 live births. Maternal viraemia postpartum, maternal HIV seroprevalence and ART coverage during ANC positively correlated with cases of MTCT, while higher proportions of women with fANC booking <20 weeks’ gestation were associated with a decline in MTCT cases. Conclusions. Findings suggest that maternal viraemia postpartum, geographical areas with a higher burden of maternal HIV, women initiating ART late in pregnancy and/or incident maternal HIV during pregnancy are significant population-level predictors of MTCT in the national prevention of MTCT programme. Scale-up of HIV prevention services is required to lower maternal HIV prevalence, while expanded access to HIV testing will fast-track ART initiation among WRLHIV. Increased VL monitoring is critical to improve VL suppression rates for elimination of MTCT.