Breast Milk Found to Contain Coronavirus in First Case of Its Kind

The breast milk of a mother with COVID-19 has tested positive for the coronavirus, according to scientists. However, it remains unclear whether the virus can be passed on in the fluid.

The correspondence, published in the journal The Lancet is thought to be the first example of SARS-CoV-2 (the coronavirus that causes COVID-19) being found in breast milk.

The authors took samples of breast milk from two women in a German hospital who had tested positive for SARS-CoV-2. To prevent the milk from being accidentally contaminated by the coronavirus, the women's nipples were disinfected before milk was collected using a pump.

Researchers analyzed the milk using a "highly sensitive technique" that detects and quantifies levels of the virus' RNA, or genetic material, co-author Jan Münch, professor at the Institute of Molecular Virology at Ulm University, Germany, told Newsweek.

Four samples were collected from one unnamed woman once on days 12 and 13 of her hospital admission, and twice on day 14. Her milk tested negative each time. The woman had mild COVID-19 symptoms on the first few days of her hospital stay, but not when her milk was taken.

Milk from the second mother tested positive for four consecutive days while she had mild COVID-19 symptoms. Two samples taken in the latter days of her symptoms tested negative.

Her baby tested positive for the coronavirus, but the team aren't sure if the infant caught the virus from the mother's breast milk or if there was another mode of transmission. The mother had been wearing a mask since her COVID-19 symptoms started, and took precautions when handling and feeding her baby, including cleaning her hands and breasts, and sterilizing pumps and tubes, according to the researchers.

Münch stressed the findings are anecdotal as the team only found the viral RNA in samples from one woman.

Subsequent studies are needed to analyze "in detail" how many nursing mothers carry SARS-CoV-2 RNA in their breast milk, whether the virus is infectious, and if it could really be transmitted to the newborn, he said. Other viruses, such as HIV-1, are known to be passed on in breast milk.

Since the COVID-19 pandemic started five months ago, the ability for the virus to pass from mother to baby is one of the many questions that have arisen about the little-understood coronavirus. Research published in the New England Journal of Medicine in April where the breast milk of three women was tested found no evidence of SARS-CoV-2, but that also had a small sample size.

SARS-CoV-2 is a member of the large family of coronavirus bugs, which includes SARS-CoV, the cause of severe acute respiratory syndrome (SARS), MERS-CoV of Middle East Respiratory Syndrome (MERS), and others that trigger some common colds. Münch and his team were surprised to find SARS-CoV-2 in the samples, as coronaviruses have never been detected in human milk "and thus breastfeeding of newborns by SARS-CoV-2 infected mothers has been considered safe."

In light of these findings and the fact that it is possible to be infected by SARS-CoV-2 and not show symptoms immediately or at all, should women avoid breastfeeding during the COVID-19 pandemic?

Münch said: "I think that asymptomatic mothers do not shed the virus into milk and would still recommend breastfeeding. For symptomatic mothers one could think about collecting milk and testing it for the presence of SARS-CoV-2 before feeding. An alternative could be pasteurization, however, it has not yet been demonstrated that this procedure inactivates the virus."

In guidance on breastfeeding released by the U.S. Centers for Disease Control and Prevention on May 5, before Münch's research was published, the agency stated: "We do not know whether mothers with COVID-19 can transmit the virus via breast milk, but the limited data available suggest this is not likely to be a source of transmission.

"A mother with confirmed COVID-19 should be counseled to take all possible precautions to avoid spreading the virus to her infant, including hand hygiene and wearing a cloth face covering."

Over 333,000 people have died of COVID-19 in 5.1 million cases worldwide since late last year, according to Johns Hopkins University. Some 1.9 million people have recovered. The U.S. is the country with the most known cases, as the graphic below by Statista shows.

Countries with the most confirmed COVID-19 cases.
Countries with the most confirmed COVID-19 cases. STATISTA