Maternal virus load and perinatal human immunodeficiency virus type 1 subtype E transmission, Thailand

To determine the rate and risk factors for human immunodeficiency virus (HI V)-1 subtype E perinatal transmission, with focus on virus load, pregnant H IV-infected women and their formula-fed infants were followed prospectively in Bangkok, Of 281 infants with known outcome, 68 were infected (transmiss ion race, 24.2%; 95% confidence interval, 19.3%-29.6%). Transmitting mother s had a 4.3-fold higher median plasma HIV RNA level at delivery than did no ntransmitters (P < .001), No transmission occurred at <2000 copies/mL. On m ultivariate analysis, prematurity (adjusted odds ratio [AOR], 4.5), vaginal delivery (AOR, 2.9), low NK cell percentage (AOR, 2.4), and maternal virus load were associated with transmission. As RNA quintiles increased, the AO R for transmission increased linearly from 4.5 to 24.8. Two-thirds of trans mission was attributed to virus load >10,000 copies/mL. Although risk is mu ltifactorial, high maternal virus load at delivery strongly predicts transm ission. This may have important implications for interventions designed to reduce perinatal transmission.