and Alberto Vierucci,1 for the Italian Study Group

This prospective multicenter study evaluated separately the significance of maternal injection drug use (IDU) and human immunodeficiency virus type 1 (HIV-1) coinfection in vertical trans-mission of hepatitis C virus (HCV). In all, 1372 consecutive, unselected HCV antibody – positive mothers and their infants were studied. Maternal HIV-1 coinfection (crude odds ratios [OR], 1.41; 95 % confidence interval [CI], 1.16–1.66; P .007) and IDU (OR, 1.58; 95 % CI, 1.37–1.78; P,.00001) were linked to mother-to-child HCV transmission in unadjusted analysis when all anti–HCV-positive mothers were evaluated. When only HCV RNA–positive mothers were evalu-ated, maternal IDU, but not maternal HIV-1 coinfection, was significantly associated with mother-to-child HCV transmission. Multivariable analysis confirmed the link between maternal IDU and HCV transmission (adjusted OR [AOR], 1.51; 95 % CI, 1.19–1.92; P .0006), but no association was found with HIV-1 coinfection (AOR, 0.98; 95 % CI, 0.73–1.33; P .93). IDU, but not HIV-1 co-infection, seems to be a preeminent risk factor for vertical HCV transmission. Mother-to-child hepatitis C virus (HCV) transmission has been studied extensively, and correlates of transmission have been largely discussed. Previous reports showed transmission rate