Mother-to-infant transmission of hepatitis C virus: rate of infection and assessment of viral load and IgM anti-HCV as risk factors.

One hundred twenty-six mother-infant couples were studied and 105 exposed babies were monitored for at least 12 months to define the risk of mother-to-infant HCV transmission. Infection occurred in 5 out of 76 infants (6.6%) born to 69 viraemic mothers and in none of 29 born to 26 non-viraemic mothers. Only one child was HCV RNA positive one month after birth, while the remaining children became positive at the 3rd to 4th month. HCV genotypes of the babies matched those of their mothers. No difference was found between women who transmitted the virus and those who did not with regard to age, history of drug abuse, HIV infection, ALT abnormal values, HCV genotype, type of delivery, and breast-feeding. Four out of 5 infected infants were born to mothers with IgM anti-HCV (P = 0.04). The mean viral titre in transmitting women (10(7.2)) was higher than in non-transmitting (10(6.5)), and the proportion of mothers with viral load > or = 10(7) was statistically higher in transmitting than non-transmitting women (P = 0.03). These data show that HCV perinatal infection is a rare event and suggest that IgM positivity and high viral load (> or = 10(7)) in the mother are independent variables correlated with HCV transmission (O.R. = 14.5; 95% CI: 1.3-160.7 and O.R. = 16.3; 95% CI: 1.5-179.9, respectively).