OBJECTIVE. Enterovirus infections are frequent in infants and may cause severe complications. We set out to assess whether breastfeeding can protect against these infections and whether such an effect is related to maternal antibodies in breast milk or in the peripheral circulation of the infant.
METHODS. One hundred fifty infants who were prospectively followed up from birth were monitored for enterovirus infections. The duration of breastfeeding was recorded, and maternal breast milk and blood samples were regularly taken at 3-month intervals for the detection of enterovirus antibodies and RNA. Maternal serum was available from early pregnancy, delivery, and 3 months postpartum.
RESULTS. Enterovirus infections were frequent and were diagnosed in 43% of infants before the age of 1 year and in 15% of the mothers during pregnancy. Infants exclusively breastfed for >2 weeks had fewer enterovirus infections by the age of 1 year compared with those exclusively breastfed for ≤2 weeks (0.38 vs 0.59 infections per child). High maternal antibody levels in serum and in breast milk were associated with a reduced frequency of infections. This effect was seen only in those infants breastfed >2 weeks, indicating that breast milk antibodies mediate this effect. Enterovirus RNA was not found in any of the breast milk samples.
CONCLUSIONS. These results suggest that breastfeeding has a protective effect against enterovirus infections in infancy. This effect seems to be mediated primarily by maternal antibodies in breast milk.