Microbial Safety of Donor Human Milk Before Pasteurization: Seasonal, Maternal, and Procedural Determinants Publisher Pubmed



Dalili H ; Shariat M ; Arooni Kashani H ; Sahebi L
Source: International Breastfeeding Journal Published:2026

Abstract

Background: Donor human milk (DHM) is a vital alternative for preterm infants when maternal breastfeeding is unavailable, yet its microbial safety remains a critical concern. This study provides the first longitudinal evaluation of DHM contamination patterns in Iran, aiming to identify maternal, procedural, and seasonal risk factors to inform safer milk bank practices. Methods: This repeated cross-sectional study evaluated microbial contamination in DHM over six years (2019–2025) at Valiasr Hospital’s Human Milk Bank (HMB) in Tehran. Samples were stratified into two phases following a protocol revision in October 2023, which introduced agar-based culturing and enhanced hygiene practices. Maternal, environmental, and seasonal variables were recorded for each donation. Pathogen-specific contamination rates were analyzed, and multivariate logistic regression identified independent predictors. Firth’s penalized likelihood method was applied to ensure statistical stability in sparse data models. Results: Of 509 DHM samples screened, 40.7% were excluded due to microbial contamination, while all 302 pasteurized samples tested pathogen-free. The transition to agar-based culturing and upgraded hygiene protocols in Phase II reduced discard rates and seasonal variation, with Staphylococcus epidermidis dropping from 21.3% to 3.2%. Klebsiella pneumoniae emerged as the dominant pathogen in Phase II (17.6%), with seasonal peaks in cooler months. Multivariate regression analysis identified manual expression as a significant predictor of Bacillus cereus contamination. For Staphylococcus epidermidis, longer intervals between childbirth and donation, as well as home refrigeration (vs. freezing), were independently associated with increased contamination risk. No significant associations were found for Klebsiella pneumoniae, Staphylococcus aureus, or Escherichia coli, suggesting pathogen-specific risk dynamics. Conclusion: This study establishes a foundational microbiological profile of DHM in Iran, demonstrating that rigorous pasteurization protocols ensure pathogen-free milk for NICU use. The integration of maternal, procedural, and seasonal variables revealed key contamination drivers and highlighted the impact of methodological upgrades on microbial detection. Findings support the refinement of exclusion thresholds and culture techniques to balance safety with milk availability. These insights provide a critical framework for optimizing DHM governance in emerging milk bank systems. © The Author(s) 2025.