Some mothers are worried about transmitting the novel coronavirus to their newborns during nursing, after it was reported in Japan that a mother's breastmilk tested positive for the virus causing COVID-19.

Medical organizations differ on how to tackle the issue, although at least one doctor is urging calm, arguing that there is no evidence of a child being infected through breastfeeding.

Japanese media reported on July 9 that breastmilk of a young mother from the western prefecture of Wakayama tested positive for the novel coronavirus.

The woman had been hospitalized after testing positive for the virus in April. She had a polymerase chain reaction test on her breastmilk to see if she could continue nursing her infant, and the test came back positive. At the time, the woman suffered from mastitis, or inflammation of the breast tissue, and a fever.

Two days later, a new test on her breastmilk was negative.

The prefecture suggested two possible explanations for the conflicting results.

The first was that the virus may have leaked out during nursing due to the mastitis. The breastmilk of another mother who contracted the virus but had no inflammation of breast tissue was negative.

The second involved the possibility that the breastmilk was contaminated when it was being extracted for testing.

Concern over transmission of the virus via breastfeeding is widespread but health bodies differ in their approach to the issue and the level of risk they attach to it.

The World Health Organization stated last week that the risk of COVID-19 infection from breastfeeding is negligible and has never been documented, in a call for greater support for using mother's milk over substitutes.

In June, it had recommended mothers to continue nursing with breastmilk since it contains nutrients and antibodies, but to do so after taking protective measures against the virus such as mask-wearing, hand-washing and sanitizing.

The same month, however, the Japan Society of Obstetrics and Gynecology put out a notice stating, "Since there are reports of the novel coronavirus discovered in breastmilk, we believe infants of virus-carrying mothers should be fed only with formula for at least a month after birth." It also recommended separating the infant and mother until both had tested negative for the virus.

The Japan Pediatric Society also said infants should not be breastfed as contact spreads the disease, but added, "As long as the mother's health is stable, babies can be nursed with their mother's milk."

Mothers say that they are confused.

"In the end I really don't know what to do," said a 38-year-old mother from Tokyo who has a 10-month-old girl. "My daughter doesn't like powdered milk. I want to continue nursing her until there is evidence of a clear link between the coronavirus and breastmilk."

Yuka Wada, a neonatology doctor at the National Center for Child Health and Development and a representative of the Japanese Association of Lactation Consultants, urged mothers to remain calm.

"At this point, there are no reports of coronavirus transmission via breastmilk. PCR testing is ultimately a test that seeks to determine the presence of the virus, not to tell us how infectious the disease is. Please know that you are not in imminent danger if your milk tests positive," she said.

Medical institutions should not mechanically suggest that an infected mother should be separated from her infant or should only use powdered formula, Wada said.

"It is necessary for medical institutions to take into account mothers' feelings," she added.