Infant infections associated with expressed breast milk: a scoping review

Human breast milk is widely recognized as optimal infant nutrition, and expressed breast milk (EBM) is increasingly used in both home and neonatal intensive care unit (NICU) settings. However, milk expression introduces opportunities for microbial contamination and growth not present during direct breastfeeding. Despite documented case reports of infant infections associated with EBM, the relative importance of different contamination pathways and pathogens remains poorly characterized.

To identify and synthesize published case reports of infant bacterial and fungal infections associated with EBM, characterizing affected populations, implicated pathogens, contamination routes, and the strength of epidemiological evidence linking EBM to infection.

A scoping review was conducted following PRISMA guidelines. Medline, Scopus, CINAHL, and the Cochrane Library were searched through January 2026. Eligible studies included case reports describing bacterial or fungal infection in infants where EBM was a suspected infection source. Studies were limited to those published after 2000 and containing sufficient detail. All studies were from countries classified as upper-middle or high-income.

Forty-eight case reports across 43 studies were identified, involving 142 infants and 15 pathogen species. Infections predominantly affected very preterm, very low birthweight infants in NICUs. Among infected infants with reported outcomes, 23% (17/73) died during the reported clinical course. The most frequently implicated pathogens were S. agalactiae, C. sakazakii, S. aureus, S. marcescens, K. pneumoniae, and B. cereus. Epidemiological evidence linking EBM to infection was frequently limited by inconsistent sampling timing, infrequent environmental testing, and variable use of molecular subtyping.

EBM-associated infections appear to be rare and primarily affect vulnerable preterm infants, but the available evidence is derived from published case reports which are subject to publication bias and frequently had methodological limitations. The relevance of milk expression to infection risk varies by contamination pathway and pathogen, suggesting that preventive strategies should be tailored accordingly.