A REVIEW OF HEPATITIS-C VIRUS (HCV) VERTICAL TRANSMISSION - RISKS OF TRANSMISSION TO INFANTS BORN TO MOTHERS WITH AND WITHOUT HCV VIREMIA OR HUMAN-IMMUNODEFICIENCY-VIRUS INFECTION

Background Hepatitis C virus (HCV) vertical transmission studies have reported conflicting findings, possibly due to differences in HCV tran smission risk factors among maternal populations, or to methodological differences. Methods Systematic review of worldwide published and unp ublished HCV vertical transmission studies. Standardized diagnostic cr iteria were applied to minimize methodological differences, and transm ission rates recalculated according to maternal HCV viraemic and human immunodeficiency virus (HIV) infection status. Results In all, 976 el igible infants from 28 studies were followed up sufficiently for recal culation of transmission rates. Overall transmission rates were less t han 10% in 8/12 studies of HIV negative mothers, compared with 2/7 stu dies comprising at least 50% HIV-coinfected mothers. Rates from 409 vi raemic mothers in 15 studies ranged from O% to 41%, being less than 10 % from HIV negative mothers in 6/13 studies and from HIV positive moth ers in 1/6 studies. Nine studies measured maternal viraemia levels, wi th only 2/30 transmitting mothers having <10(6) copies/ml of HCV RNA. Eight transmissions were identified overall from non-viraemic mothers. Significant transmission rate variation remained after accounting for maternal viraemia and HIV coinfection, possibly due to differences in other vertical transmission risk factors, in frequencies of postnatal transmission, or residual differences in study methodologies. Conclus ions Overall, HCV transmission is largely restricted to infants born t o HCV viraemic mothers, and low risks among most HIV negative mothers may be due to lower HCV viraemia levels. International agreement on st andardized diagnostic criteria for HCV vertical transmission would fac ilitate pooling of individual findings, to allow more precise transmis sion estimates and further investigation of risk factors.