The effect of maternal viral load on the risk of perinatal transmission of HIV-1

Objective: To determine the effect of maternal viral load at delivery on the risk of perinatal transmission of HIV-1. Design: A nested case-control study within a prospectively followed cohort of HIV-1-infected pregnant women and their infants. Setting: The multicenter New York City Perinatal HIV Transmission Collaborative Study. Participants: Fifty-one women who gave birth to HIV-1-infected infants were frequency-matched within CD4+ cell count quintiles with 54 non-transmitting mothers. Main outcome measures: Maternal quantity of HIV-1 viral RNA was assayed in plasma obtained near delivery using the nucleic acid sequence-based amplification assay system. Results: Viral RNA was detected in 73 (70%) out of 105 women and the median viral load was 16,000 RNA copies/ml in transmitters and 6600 in non-transmitters (P < 0.01). When adjusted for maternal CD4+ count near delivery, women with measurable viral load were nearly sixfold more likely to transmit HIV-1 than women with viral load below detection [adjusted odds ratio (AOR), 5.8; 95% confidence interval (CI), 2.2-15.5]. The odds ratio for perinatal transmission of log₁₀ viral load, adjusted for CD4 count was 2.7 (95% CI, 1.5-5.1). When stratified by the stage of HIV-1 disease, the only group with significant association between log₁₀ viral load and transmission were AIDS-free women with CD4+ count > 500 x 10⁶/l (AOR, 9.1; 95% CI, 2.6-31.5). Conclusions: High maternal viral load increases the likelihood of perinatal transmission of HIV-1 in women without AIDS and advanced immunosuppression. HIV-l-infected pregnant women without advanced disease, shown by others to have the lowest risk of perinatal transmission, may benefit the most from efforts to identify and decrease viral load at delivery.