Should NICU Donor Milk Be Screened Before Pasteurization?

Updated: Dec 7, 2020

Processing donor human milk for distribution requires steps to ensure safety for infant recipients, especially those who are immunocompromised and at-risk.

There is, however, an important step that is surprisingly not required of all human milk banks. That important step can identify heat-resistant bacteria that could potentially survive a pasteurization process. It’s one you should know about, and something you should expect from your donor milk provider.

Here’s what you need to know about pooled milk screening before pasteurization.

The difference between donor pre-screening and pooled milk pre-screening

Every donor milk bank or company should pre-screen applicants who wish to donate breastmilk. That’s a given, and is a vital step to ensuring milk quality and safety. Screening donors can identify communicable diseases as well as risk factors such as drug use which make their milk unfit for infants. Applicant screening is conducted through blood tests and questionnaires, and is typically carried out in concert with medical professionals.

An additional step is to screen milk before pasteurization or sterilization. Pre-screening milk helps to identify heat-resistant bacterial spores as well as organisms which can contaminate milk with heat-resistant toxins. Milk identified to contain unsafe bacteria can then be discarded to eliminate it entirely from the milk pool prior to pasteurization or sterilization.

Would you believe not all human milk banks include this raw milk pre-screening step?

Heat-resistant bacteria in donor human milk

Bacillus cereus is an example of heat-resistant bacteria. One study found that over 30% of their milk samples were contaminated by Staphylococcus aureus and Bacillus cereus prior to pasteurization. The Holder pasteurization process then fully eliminated Staphylococcus aureus, but NOT Bacillus cereus.1

Retort sterilization eliminated all B. cereus from raw milk, but only a few human milk banks or companies use that process. Medolac is one. However, for all others using Holder pasteurization, there is an added risk of B. cereus survival if they do not screen before pasteurization.

The reason for its survival is found in the B. cereus endospores, which can survive temperatures that would otherwise destroy foodborne pathogen cells.2

B. cereus can be devastating to a fragile preterm infant, causing bloodstream, lung, and central nervous system infections with an unfortunately high mortality rate.3 Testing for B. cereus before pooling and processing raw human milk is highly recommended for that reason.

Decousser et al studied B. cereus-related severe intestinal infections in preterm neonates and the relationship to pooled human milk (PHM). They concluded with, “Careful monitoring of conditions during collection, conservation, and administration of PBM should be implemented in high-risk populations such as premature infants.”4

Other countries have made strides to pre-screen their pooled donor milk before processing. France has implemented a bacteriologic testing process before pasteurization to identify risks such as B. cereus. In fact, they discard about 11% of their breastmilk before pooling and pasteurization.1 Companies in the United States who also follow a milk pre-screening process, such as Medolac, find a similar percentage to discard to eliminate B. cereus contamination.

Heat resistant toxins in pooled milk

In addition to the possibility of infection with B. cereus, Staph aureus, a bacteria present in breastmilk, can produce a harmful toxin. While S. aureus is destroyed by pasteurization, its toxin is not, and can still make infants sick even after the bacteria which produced the toxin are destroyed.

By screening milk before pasteurization for S. aureus, the risk of toxin can be controlled. However, if milk is only screened for S. aureus after pasteurization, the toxin could be present even though the bacteria has all been killed. This conundrum can be solved in two ways. The first is to test for the organism before pasteurization and eliminate milk with high S. aureus counts. The second is to test for presence of the toxin in the finished product. Unfortunately, many milk banks test with neither of these methods.

Why don’t all milk banks pre-screen pooled milk?

Not all human milk banking organization guidelines include the process of pre-screening raw milk before pasteurization. While some choose to perform this screening process, others do not. Those who do not, and who also use a Holder pasteurization method, could risk active B. cereus spores in the milk.

It is possible those who do not engage in the pooled milk pre-screening practice do so to save time and money and preserve a larger supply of raw milk.

Whatever the reason, understanding the raw milk pre-screening process is meaningful to healthcare professionals who select donor human milk resources for their NICU and well-baby patients.

Pre-screening pooled milk is a valuable step

It’s worth asking the donor milk companies or banks you work with about their full process, and understanding how they remove bacteria from pooled milk – not only during pasteurization or sterilization, but before and after.

Delivering donor human milk nutrition to infants who need it is a huge step to helping them overcome health challenges and improving their odds.

And so is verifying it has been tested and prepared for optimal outcomes.

Learn more about our Benefit Human Milk products, which are pre-screened before sterilization, and trusted by NICUs across the country.



1. Capriati, et al (2019). A modified holder pasteurization method for donor milk: Preliminary data. Nutrients, 11(5), 1139.

2. Schneider et al (2017). Preventing foodborne illness: Bacillus cereus. University of Florida. Accessed online May 21 2020.

3. Hilliard et al (2003). Bacillus cereus bacteremia in a preterm neonate. Journal of Clinical Microbiology, 41(7), 3441-3444. Accessed online May 31 2020.

4. Decousser at al. (2013). Bacillus cereus and severe intestinal infections in pre-term neonates: Putative role of pooled breast milk. American Journal of Infection Control, 41(10), 918-921.