Health professionals have long deemed breast milk to be the healthiest food to feed an infant, providing a baby with protection from infections and diseases. But a new study suggests that human breast milk purchased from the internet may actually cause illness rather than prevent it.

Researchers from the Nationwide Children's Hospital, Cincinnati Children's Hospital Medical Center and Ohio State University say that almost three-quarters of human breast milk samples tested contained high levels of harmful bacteria that may cause illness, with the team even coming across fecal contamination.

Their study - which they say is the first to examine the safety of selling breast milk to others online - is published in the journal Pediatrics.

According to the researchers, selling breast milk online has become increasingly common over recent years. They note that in 2011, a study showed that around 13,000 postings were placed on milk-sharing websites in the US.

However, they note that it has been unclear as to whether breast milk purchased online is safe for infants to consume.

In order to find out, the research team purchased breast milk online from various public websites advertising the milk for sale. They only responded to sellers who did not require information regarding the infant receiving the milk, and who did not require a phone call prior to the transaction.

The team analyzed 101 samples bought online and compared these with 20 samples from a non-profit milk bank that follows guidelines from the Human Milk Banking Association of North America.

'Surprising' levels of harmful bacteria

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Researchers say that 75% of breast milk samples bought online contained high levels of harmful bacteria.

The researchers found that 74% of the internet breast milk samples contained high bacterial counts or Gram-negative bacteria that can cause infections such as pneumonia and meningitis.

Furthermore, 64% of the internet samples tested positive for staphylococcus - a bacteria that can cause an array of infections ranging from a skin abscess to septicemia.

The researchers also found salmonella present in three of the internet-bought samples, while fecal contamination was discovered in others.

Sarah A. Keim, principal investigator of the Center for Biobehavioral Health at Nationwide Children's Hospital, comments:

"We were surprised so many samples had such high bacterial counts and even fecal contamination in the milk, most likely from poor hand hygiene. We were also surprised a few samples contained salmonella.

Other harmful bacteria may have come from the use of either unclean containers or unsanitary breast milk pump parts."

Breast milk 'not safe to purchase online'

The researchers say that this research provides evidence that it is not safe to purchase human breast milk online, since shipping and storage practices, and lack of available information regarding the donor's health and hygiene methods, clearly contribute to the high levels of bacteria discovered.

They found that the longer the milk took to ship, the more contaminated the milk was.

Furthermore, they found that 19% of sellers did not include dry ice or other cooling methods to keep the milk inside the recommended temperature range, and 17% of these samples showed significantly high levels of one or more types of bacteria.

When purchasing the milk online, the researchers found that the majority of sellers did not include relevant hygiene information in their listings regarding the handling of the breast milk or their storage practices.

There was also lack of information regarding whether the donor had any diseases that could potentially be transmitted to the milk, or whether they were taking any form of medication or harmful drugs.

"Major milk-sharing websites post a lot of guidance about milk collection, storage, shipping and provider screening. However, results from this study showed sellers do not often follow this advice because hygiene and shipping practices were often compromised," says Dr. Keim.

"Based on our research, it is not safe to buy breast milk online, and the Food and Drug Administration (FDA) recommends against sharing milk obtained in that way.

Recipients are not able to determine for sure if the milk has been tampered with, or contains harmful drugs or pharmaceuticals, or if the information the provider supplied about their health was truthful."

Although the researchers say that it is difficult to know whether an infant could be sickened by consuming internet-bought breast milk, the samples from this study contained bacteria that could cause illnesses linked to contaminated breast milk.

Dr. Keim notes that contaminated breast milk can be particularly harmful for premature babies and those with weaker immune systems as they are already susceptible to infection.

Breast milk banks 'a safer alternative'

The researchers emphasize that breast milk banks are a "safer alternative" to purchasing breast milk online for mothers who are unable to produce their own breast milk.

Breast milk banks select milk from carefully screened donors and the milk is then pasteurized, meaning any harmful bacteria is killed before the milk reaches an infant.

Dr. Keim adds that mothers who have extra breast milk should also consider donating it to a milk bank rather than selling it online, as it will be handled properly and go to an infant who badly needs it.

However, she says that their findings do not apply to situations where milk is shared among friends or family, as the risks in those situations are not well understood.

She adds that mothers who are breast feeding their own child should ensure the parts of the breast pump that come into contact with the milk are well sanitized, that clean containers are used and that hands are washed before pumping and handling milk in order to minimize contamination.

She says it is also important to keep the milk cold. The Mayo Clinic says that freshly expressed breast milk can be kept at room temperature for up to 6 hours but recommends that if the milk is not used within this time or if the room is particularly warm, it should be transferred to an insulated cooler, refrigerator or freezer.

Dr. Keim says that the research team's goal is to identify infant feeding practices "that optimize child and maternal health."

"We will continue to study breastfeeding in the context of contemporary society, since where and how infants are fed is rapidly changing," she says.

Earlier this year, Medical News Today reported that the Centers for Disease Control and Prevention released data showing that breastfeeding in the US is increasing.