Factors associated with vertical transmission of HIV in the Western Cape, South Africa: a retrospective cohort analysis

Abstract Introduction Monitoring mother‐infant pairs with HIV exposure is needed to assess the effectiveness of vertical transmission (VT) prevention programmes and progress towards VT elimination. Methods We used routinely collected data on infants with HIV exposure, born May 2018–April 2021 in the Western Cape, South Africa, with follow‐up through mid‐2022. We assessed the proportion of infants diagnosed with HIV at birth (≤7 days), 10 weeks (>1 to 14 weeks) and >14 weeks as proxies for intrauterine, intrapartum/early breastfeeding and late breastfeeding transmission, respectively. We used mixed‐effects Poisson regression to assess factors associated with VT in mothers known with HIV by delivery. Results We included 50,461 infants born to mothers known with HIV by delivery. HIV was diagnosed in 894 (1.8%) infants. Among mothers, 51% started antiretroviral treatment (ART) before and 27% during pregnancy; 17% restarted during pregnancy after ≥6 months interruption; and 6% had no recorded ART during pregnancy. Most pregnancy ART regimens included non‐nucleoside reverse transcriptase inhibitors (83%). Of mothers with available results (90% with viral load [VL]; 70% with CD4), VL nearest delivery was 14 weeks. Among these infants, 0.9%, 0.4% and 1.5% were diagnosed positive at birth, 10 weeks and >14 weeks, respectively. Among infants diagnosed with HIV, 43%, 16% and 41% were diagnosed at these respective time periods. Among mothers with VL