Human milk safety and infection control challenges in the NICU

Human milk fed directly from the breast contains optimal nutritional, protective and bioactive components. When preterm infants are unable to breastfeed, the challenging aim for the NICU is to provide human milk in a way that is as close to direct breastfeeding as possible and to retain the integrity and safety of expressed milk.
Medela human milk safety challenges

Due to the intricate nature of human milk and the complex pathway required to prepare it for feeding, NICU safety and infection control must manage three main issues:

  • the bacterial load in human milk
  • the milk being potentially exposed to pathogens during expression and handling
  • risks of mix-ups, and the subsequent delivery of milk to the incorrect infant

Milk collection, storage and labelling practices can be among the sources of these risks. Despite the challenges, it is widely recognised that the benefits of receiving human milk, particularly the infant’s own mother’s milk, outweigh the risks associated with human milk handling.

Risk factors in human milk

Fresh human milk contains bacteria that are thought to contribute to the vital programming of the infant’s immune system. But potentially pathogenic bacteria are also common in human milk. This can lead to occasions where feeding an infant their own mother’s milk (OMM) is contraindicated.

Furthermore, medications and other substances, such as alcohol and nicotine, may be present in the mother’s body. While the list of medications that are contraindicated during lactation is fairly short, each maternal-infant situation must be evaluated individually.

Concerns when handling human milk

Human milk can become contaminated at various points along the milk pathway, including pumping, storage and handling processes. In the NICU setting, even the most benign flora may have a negative effect on the vulnerable, immunocompromised infant. Consequently, it is critical that during processing the anti-infective properties be maintained as much as possible, while avoiding the entry of pathogenic organisms. Milk storage should therefore be optimised in terms of duration, temperature and labelling.

After storage, milk preparation most likely requires thawing, warming and fortification. Each process may affect the composition of the milk and jeopardise its hygiene. Microwaving milk or using hot or boiling water is not recommended since this destroys the anti-infective properties of the milk. In addition, microwaves have been shown to warm milk unevenly, creating ‘hot spots’ that can compromise the temperature safety of the milk and lead to scalds.

Human milk, particularly donor milk, is pasteurised to prevent the potential transmission of pathogens. Holder pasteurisation is a widely used low-temperature long-time heat treatment (62.5 °C for 30 min). However, heat treatment is well known to also result in significant loss of immunological and anti-inflammatory components, probiotic bacteria and white blood cells in milk. In addition, pasteurisation has been shown to negatively impact the ability of the milk to resist bacterial growth.

Consequently, there are different management processes and recommendations in place for pasteurised and unpasteurised milk. NICU professionals should be aware that they may need to take even more care with pasteurised milk, particularly with storage conditions, in order to control bacterial growth.


Jeurink,P.V. et al. Human milk: A source of more life than we imagine. Benef Microbes 4, 17-30 (2013).

Human Milk Banking Association of North America 2011 Best practice for expressing, storing and handling human milk in hospitals, homes, and child care settings (HMBANA, Fort Worth, 2011).

Novak, F.R., Da Silva, A.V., Hagler, A.N., & Figueiredo, A.M. Contamination of expressed human breast milk with an epidemic multiresistant Staphylococcus aureus clone. J Med Microbiol 49, 1109-1117 (2000).

Eidelman,A.I. & Szilagyi,G. Patterns of bacterial colonization of human milk. Obstet Gynecol 53, 550-552 (1979).

Carroll, L., Osman, M., Davies, D.P., & McNeish, A.S. Bacteriological criteria for feeding raw breast-milk to babies on neonatal units. Lancet 2, 732-733 (1979).

Perez,P.F. et al. Bacterial imprinting of the neonatal immune system: Lessons from maternal cells? Pediatrics 119, e724-e732 (2007).

Quan,R. et al. Effects of microwave radiation on anti-infective factors in human milk. Pediatrics 89, 667-669 (1992).

Sigman, M., Burke, K.I., Swarner, O.W., & Shavlik,G.W. Effects of microwaving human milk: Changes in IgA content and bacterial count. J Am Diet Assoc 89, 690-692 (1989).

Christen, L., Lai, C.T., Hartmann, B., Hartmann, P.E., & Geddes, D.T. The effect of UV-C pasteurization on bacteriostatic properties and immunological proteins of donor human milk. PLoS One 8, e85867 (2013).