SARS-CoV-2 Appears Unlikely to Pass Through Breast Milk

Heidi Splete

August 31, 2020

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Breast milk is an unlikely source of transmission of SARS-CoV-2 from mothers to infants, according to data from case reports and breast milk samples from 18 women.

"To date, SARS-CoV-2 has not been isolated from breast milk, and there are no documented cases of transmission of infectious virus to the infant through breast milk," but the potential for transmission remains a concern among women who want to breastfeed, wrote Christina Chambers, PhD, of the University of California, San Diego, and colleagues.

In a research letter published in JAMA, the investigators identified 18 women with confirmed SARS-CoV-2 infections (all but 1 of the women had symptomatic COVID-19 disease) and infants aged 0-19 months between March 27 and May 6, 2020. The average age of the mothers was 34 years, and 78% were non-Hispanic White. The women provided 1-12 samples of breast milk for a total of 64 samples collected before and after positive COVID-19 tests.

One sample yielded detectable RNA from SARS-CoV-2 and was collected on the day of the woman's symptom onset. However, one sample taken 2 days prior to symptom onset and two samples collected 12 and 41 days later tested negative for viral RNA, the researchers said. In addition, no replication-competent virus was identified in the positive sample or any of the other samples.

The researchers spiked two stored milk samples collected prior to the pandemic with replication-competent SARS-CoV-2. Virus was not detected by culture in the samples after Holder pasteurization, but was detected by culture in nonpasteurized aliquots of the same samples.

"These data suggest that SARS-CoV-2 RNA does not represent replication-competent virus and that breast milk may not be a source of infection for the infant," Dr. Chambers and associates said.

The results were limited by several factors including the small sample size and potential for selection bias, as well as the use of self-reports of positive tests and self-collection of breast milk, the researchers noted. However, the findings are reassuring in light of the known benefits of breastfeeding and the use of milk banks.

"This research is important because the pandemic is ongoing and has far-reaching consequences: as the authors indicate, the potential for viral transmission through breast milk remains a critical question for women infected with SARS-CoV-2 who wish to breastfeed," Janet R. Hardy, PhD, MPH, MSc, a consultant on global maternal-child health and pharmacoepidemiology, said in an interview.

"This virus has everyone on a rapid learning track, and all information that helps build evidence to support women's decision-making in the care of their children is valuable," she said. "These findings suggest that breast milk may not be a source of SARS-CoV-2 infection for the infant. They provide some reassurance given the recognized benefits of breastfeeding and human milk."

However, "This study is very specific to breast milk," she emphasized. "In advising women infected with SARS-CoV-2, clinicians may want to include a discussion of protection methods to prevent maternal transmission of the virus through respiratory droplets."

Although the data are preliminary, "the investigators established and validated an RT-PCR [reverse transcription polymerase chain reaction] assay and developed tissue culture methods for replication-competent SARS-CoV-2 in breast milk, both valuable tools for further studies. Next steps will include controlled studies of greater sample size with independent verification of RT-PCR positivity," said Dr. Hardy, a consultant to Biohaven Pharmaceuticals, New Haven, Conn.

The study was supported by the National Institute of Allergy and Infectious Diseases, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and the National Institute of Mental Health. Medela Corporation provided milk sample collection materials. The Family Larsson-Rosenquist Foundation provided an unrestricted COVID19 emergency gift fund. The Mothers' Milk Bank at Austin paid for shipping costs.

SOURCE: Chambers C et al. JAMA. 2020 Aug 19. doi: 10.1001/jama.2020.15580.

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