Pasteurization Inactivates SARS-CoV-2 in Breast Milk

By Lisa Rapaport

December 19, 2020

(Reuters Health) - Holder pasteurization effectively inactivate SARS-CoV-2 present in human breast milk, a small experiment suggests.

To examine the impact of pasteurization on viral levels in breast milk, researchers obtained milk samples from five healthy human donors, spiked the samples with one of five different SARS-CoV-2 isolates, then compared viral infectivity after 30 minutes at room temperature or at the pasteurization temperature of 63 degrees Celsius.

After 30 minutes at room temperature, all five samples were still infective, but researchers did find a 40.9% to 92.8% decrease of viral titers compared with medium control. This might be due to antiviral properties of free fatty acids in breast milk, the study team writes in Pediatrics.

Holder pasteurization - heating to 63 degrees Celsius for 30 minutes - completely eliminated infectivity of all five SARS-CoV-2 isolates.

Even though infectious virus has not yet been detected in human breast milk, these results should reassure clinicians and caregivers who might rely on expressed breast milk for infants or get donor breast milk from milk banks, the research team concludes.

"Feeding pasteurized breastmilk provides an alternative to infant formula, which lacks many of the beneficial breast milk properties," said senior study author Stephanie Pfaender of the Department for Molecular and Medical Virology at Ruhr-University Bochum in Germany.

"Even though infectious virus has not been isolated from milk, the presence of viral RNA and the possibility of transmission should not be neglected without further evidence," Pfaender said by email.

There were five isolates of SARS-CoV-2 tested in the study: BetaCoV/UKEssen, BetaCoV/Germany/Ulm/01/2020, BetaCoV/Germany/Ulm/02/2020, BetaCoV/France/IDF0372/2020, and BetaCoV/Netherlands/01.

Until now, no transmission from mother to child via milk has been reported, Pfaender said. Therefore, the World Health Organization encourages continuing breastfeeding even for SARS-CoV-2 positive women because the benefits significantly outweigh the potential risk for transmission, Pfaender added.

None of the studies to date of mothers infected with SARS-CoV-2 have directly linked breastfeeding to harmful spread of the virus, even among symptomatic mothers, said Dr. Lori Feldman-Winter, a professor of pediatrics at Children's Regional Hospital at Cooper University Healthcare and Cooper Medical School of Rowan University in Camden, New Jersey.

In cases described when the newborn tests positive for SARS-CoV-2, it's not clear if the newborn infection was transmitted via human milk, droplets or aerosol spread, in utero, during the birthing process, or even by nosocomial spread, Dr. Feldman-Winter, who wasn't involved in the study, said by email.

Even so, the study results should reassure clinicians recommending donor human milk for vulnerable newborns, even though donor milk is not routinely tested for SARS-CoV-2, Dr. Feldman-Winter added. That's because milk banks certified by the Human Milk Banking Association of North American use the Holder pasteurization method tested in the study.

At this time, the American Academy of Pediatrics advises direct breastfeeding, while encouraging mothers to practice hand hygiene and wear masks, Dr. Feldman-Winter said.

If an infected mother chooses not to nurse her newborn, however, she may express breast milk after appropriate hand hygiene, and this may be fed to the infant by other uninfected caregivers, Dr. Feldman-Winter added. In addition, mothers of NICU infants may express milk for their babies if their infection status makes them unable to enter the NICU.

SOURCE: Pediatrics, online December 17, 2020.