To determine the predictors for early versus later (breastfeeding) transmission of HIV-1.
Secondary data analysis was performed on HIV Network for Prevention Trials 012, a completed randomized clinical trial assessing the relative efficacy of nevirapine (NVP) versus zidovudine in reducing mother-to-child transmission (MTCT) of HIV-1. We used Cox regression analysis to assess risk factors for MTCT. The ViroSeq HIV genotyping and a sensitive point mutation assay were used to detect NVP resistance mutations.
In this subset analyses, 122 of 610 infants were HIV infected, of whom 99 (81.1%) were infected early (first positive polymerase chain reaction ≤56 days). Incidence of MTCT after 56 days was low [0.7% per month (95% confidence interval, CI: 0.4 to 1.0)], but continued through 18 months. In multivariate analyses, early MTCT “factors” included NVP versus zidovudine (hazard ratio (HR) = 0.57, 95% CI: 0.38 to 0.86), pre-entry maternal viral load (VL, HR = 1.76, 95% CI: 1.28 to 2.41), and CD4 cell count (HR = 1.16, 95% CI: 1.05 to 1.28). Maternal VL (6–8 weeks) was associated with late MTCT (HR = 3.66, 95% CI: 1.78 to 7.50), whereas maternal NVP resistance (6–8 weeks) was not.
Maternal VL was the best predictor of both early and late transmission. Maternal NVP resistance at 6–8 weeks did not predict late transmission.