Epidemiology of transmission of cytomegalovirus from mother to preterm infant by breastfeeding

Background Breastfeeding practices strongly influence the epidemiology of h uman cytomegalovirus infection. By contrast with term neonates. few data ar e available on transmission of infection from mothers to preterm infants du ring breastfeeding. Methods 151 mothers and their 176 preterm infants (gestational age at birth <32 weeks or birthweight <1500 g) were prospectively screened for cytomega lovirus infection by serology. virus culture, and PCR. The roles of cell-fr ee and cell-associated cytomegalovirus excretion during lactation were anal ysed longitudinally in relation to transmission, by maximum-likelihood esti mates. Findings Of the 69 seronegative breastfeeding control mothers, none had det ectable cytomegalovirus DNA in breastmilk and none of their 80 infants shed the virus in urine. The proportion of cytomegalovirus reactivation in sero positive breastfeeding mothers was 96% (73 of 76). The early appearance of viral DNA in milk whey (median 3.5 days post partum in transmitters; 8 days in non-transmitters: p=0.025) and infectious virus in milk whey (10 days a nd 16 days, respectively: p=0.005) were risk factors for transmission. The cumulative rate of transmission was 37% (27 of 73 mothers; 33 infants). The infection of the neonates had a mean incubation time of 42 days (95% CI 28 -69). About 50% of the infected infants had no symptoms, but four had sepsi s-like the symptoms. Interpretation The proportion of cytomegalovirus reactivation during lactat ion almost equals maternal seroprevalence. Breastfeeding as a source of pos tnatal cytomegalovirus infection in preterm infants has been underestimated and may be associated with a symptomatic infection.