Background The source for late-onset neonatal infections (LONI) due to group B Streptococcus (GBS) has not been fully explored. We reviewed GBS LONI cases associated with contaminated breast milk to determine whether breast milk was a possible route for neonatal infection.

Data sources A PubMed search from January 1977 to March 2013 was performed with MeSH words “Streptococcus agalactiae”, “group B Streptococcus”, “infection”, “milk”, “human”, “late-onset infection” and/or “neonate”; relevant cross references were also reviewed.

Results Forty-eight documented cases of GBS LONI matched our search criteria and were retrieved from the literature. When performed, molecular typing identified clonal isolates in the neonate and milk samples taken after LONI in all cases, with the hypervirulent sequence type 17 (ST-17) clone identified in two of these cases. Caesarean delivery combined with the absence of GBS recovery from maternal samples other than milk was noted for four cases. The rate of recurrent infections was high (35%) and, together with the data reviewed, points to a potential role of breast milk in GBS LONI.

Conclusions The cases reviewed here, together with the evidence of breast milk transmission for other pathogens, suggest that breast milk, which would account for repeated GBS transmission to the neonate, may favour gut translocation and subsequent LONI. Further investigations are nevertheless needed to study the relative importance of this contamination route compared with persistent postnatal gut colonisation and the dynamics of milk and neonatal gut colonisation.