Postnatal Cytomegalovirus Infection of Preterm and Very-low-birth-weight Infants Through Maternal Breast Milk: Does It Matter?

Background: Postnatal infection with cytomegalovirus (CMV) in very-preterm and very-low-birth-weight infants, transmitted through breast milk (BM), is potentially associated with adverse outcomes. This study aimed to investigate the incidence and clinical significance of postnatal CMV infection in a tertiary neonatal intensive care unit. Methods: Infants of CMV-seropositive mothers born in a neonatal intensive care unit in Melbourne, Australia, were observed for 14 weeks from birth in a prospective cohort study. Maternal BM and infant urine were tested weekly for CMV by culture and polymerase chain reaction, respectively. Clinical and laboratory data were collected and analyzed in relation to the infants' CMV infection status. Results: Data from 65 infants of 56 CMV-seropositive mothers were available for analysis. Of these mothers, 88% (49/56) shed CMV in their BM. Of the 58 infants exposed to CMV-positive BM, 27 (47%) became urine polymerase chain reaction CMV-positive. There was no significant difference in gestational age, birth weight, incidence of bronchopulmonary dysplasia, or necrotizing enterocolitis between the CMV-positive and CMV-negative groups. However, CMV-positive infants had a longer length of hospital stay and more episodes of prolonged neutropenia. Of the CMV-positive infants, 30% (8/27) remained asymptomatic, 48% (13/27) had symptoms categorized as mild and 22% (6/27) as severe. Conclusions: About half of preterm and very-low-birth-weight infants exposed to CMV-positive BM become infected, and a fifth develop significant clinical symptoms. Future studies should address the maternal and neonatal factors that determine the risk of mother-to-infant CMV transmission, as well as those leading to clinical deterioration and long-term sequelae.