Evaluation of SARS-CoV-2 in Breastmilk from 18 Infected Women

Abstract

To The Editor, Currently, the U.S. Centers for Disease Control and Prevention, American Academy of Pediatrics and the World Health Organization advise that women who are infected with SARS-CoV-2 may choose to breastfeed with appropriate protections to prevent transmission of the virus through respiratory droplets. However, the potential for exposure to SARS-CoV-2 through breastfeeding is currently unknown. To date, case reports on breastmilk samples from a total of 24 SARS-CoV-2-infected women have been published. Of those, viral RNA was detected in ten breastmilk samples from four women. In some but not all cases, environmental contamination as the source of the virus or retrograde flow from an infected infant could not be ruled out. We established a quantitative RT-PCR assay for SARS-CoV-2 in breastmilk with a limit of detection of 250 copies per mL and validated it by spiking breastmilk from uninfected women with known amounts of viral RNA. In addition, we established tissue culture methods to detect replication-competent SARS-CoV-2 in breastmilk. No viral RNA nor culturable virus was detected after Holder pasteurization of breastmilk samples that had been spiked with replication-competent SARS-CoV-2 (see Supplement). Between March 27 and May 6, 2020, we collected and analyzed 64 serial breastmilk samples from 18 SARS-CoV-2-infected women residing in the U.S. (see Supplement for clinical characteristics). Breastmilk samples were collected before and after women had a positive SARS-CoV-2 RT-PCR test and all but one woman had symptomatic disease (see Figure). One of the 64 breastmilk samples had detectable SARS-CoV-2 RNA by RT-PCR. The positive sample was collected on the day of symptom onset but one sample 2 days prior to symptom onset and two subsequent samples, collected 12 and 41 days later, tested negative for viral RNA. In addition, a subset of 26 breastmilk samples from nine women were tested for the presence of replication-competent virus using our established culture methods, and all were negative including the one sample that tested positive for viral RNA by RT-PCR. Although SARS-CoV-2 RNA was detected in one milk sample from one of eighteen infected women, the viral culture for that sample was negative. This suggests that SARS-CoV-2 RNA does not represent replication-competent virus and that breastmilk itself is likely not a source of infection for the infant. Furthermore, when control breastmilk samples spiked with replication-competent SARS-CoV-2 virus were treated by Holder pasteurization, a process commonly performed by donor milk banks, no replication-competent virus nor viral RNA was detectable. Further research to confirm these findings is needed, as well as an examination of convalescent milk for the presence of antibodies against SARS-CoV-2.

Detection of SARS-CoV-2 in Milk From COVID-19 Positive Mothers and Follow-Up of Their Infants

“…However, the presence of the virus in human milk was not evaluated. Recently the presence of SARS-CoV-2 in breastmilk was evaluated in 18 infected women from delivery to 19 months, with only one sample found positive (19). These data are in accordance with our results.…”

“…Finally, detection of SARS-CoV-2 RNA does not necessarily imply the presence of an infectious and active virus that can be transmitted via breastfeeding to infect the infant (19).…”

Breastfeeding during the COVID-19 pandemic – a literature review for clinical practice

“…Samples of breastmilk from 18 women infected with SARS-CoV-2 were evaluated and although SARS-CoV-2 RNA was detected in one sample of milk, the follow-up culture of the same sample was negative. It is likely that the SARS-CoV-2 RNA that was found does not contain replication-competent virus and so is unlikely to infect an infant [20]. Findings from this group of cases suggest that there is currently no evidence to show that respiratory viruses can be transmitted through breast milk.…”

Universal Screening for SARS-CoV-2 of all Human Milk Bank Samples

“…To date, there is no sure evidence that novel severe acute respiratory Coronavirus Virus 2 (SARS-CoV-2) can be transferred through human milk (Auriti et al, 2020), although an intermittent excretion of the virus has been reported (Costa et al, 2020). Furthermore, detection of viral RNA by RT-PCR in human milk does not equate with infectivity (Chambers et al, 2020). Cold storage of SARS-COV-2 in human milk did not significantly change viral load over a 48 hr period according to a study in which the virus was experimentally inoculated into human milk samples (Walker et al, 2020).…”