Disclaimer: This is a summary of an article that is in a preprint and has not been peer reviewed.
Authors in a pre-peer reviewed article established a quantitative RT-PCR assay for SARS-CoV-2 in breastmilk with a limit of detection of 250 copies per mL. They applied this to a series of 64 serial breastmilk samples from 18 SARS-CoV-2-infected women and found viral RNA in only one sample. After viral culture, they found the viral sample to be replication-incompetent and concluded that breast milk is not a source of SARS-CoV-2 infection to infants. Additionally, when control breastmilk samples were spiked with replication-competent SARS-CoV-2 virus and treated by Holder pasteurization no replication-competent virus nor viral RNA was detectable. These results suggest that the presence of SARS-Cov-2 in breast milk is not common and that using a standardised pasteurization procedure, any presence of virus is destroyed.
Summary by Clive Gray