MONDAY, Oct. 21, 2013 (HealthDay News) -- Even after working with several nursing experts, first-time mom Katie Sweet wasn't able to make enough of her own breast milk to feed her newborn daughter.
And she said her baby just didn't do well on formula.
"Honestly, my daughter is a completely different girl on breast milk. She has less stomach issues, she sleeps better and seems more alert," said Sweet, an insurance agent in Grand Junction, Colo.
For a few months, she was able to keep her daughter on a breast-milk diet with the help of two local friends who were making more milk than they needed. But when those women weaned their own infants, her supply ran out, leaving her desperate to find more.
"I would do anything to make sure she got what she needed to be happy," Sweet said.
Like growing numbers of women who've gotten the message that breast milk is the best possible food for babies, but who find themselves unable to supply their own, she turned to the Internet.
She placed a classified ad offering to buy breast milk from a stranger on a website set up to connect people who want to sell their breast milk with others looking to purchase it.
"My husband and I did a lot of research and felt comfortable with the decision to purchase milk," Sweet said.
Her comfort turned to concern, however, as she learned of the findings of a new study that tested raw breast milk bought through the Internet.
The researchers did not name the specific websites used in their study but said the contaminated samples came from a U.S. milk-sharing website that uses a classified ad format.
Of 101 samples purchased anonymously, nearly three-quarters of the samples contained bacteria that could make a baby sick, including three batches that tested positive for salmonella.
"There should not be salmonella in human milk," said Dr. Kathleen Marinelli, chair of the United States Breastfeeding Committee, a nonprofit group based in Washington, D.C.
Salmonella and other kinds of gram-negative bacteria, which were the most common types found in the study, normally live in a person's gut.
"That tells me that the person who pumped that milk used very bad hygiene. Essentially, they didn't wash their hands after using the toilet," said Marinelli, who was not involved in the study.
None of the samples tested positive for HIV (the AIDS virus), which can be passed through breast milk. But one in five tested positive for another virus called cytomegalovirus, or CMV.
CMV is common -- somewhere between 50 percent and 80 percent of people have had CMV by the time they're 40, according to the U.S. Centers for Disease Control and Prevention.
In healthy babies, CMV causes a mild flu-like illness that's rarely serious, Marinelli said. But for premature infants and those with compromised immune function, the virus can be very dangerous.
"If preemies get milk with CMV in it, they can get everything from a systemic illness that can put them back on a ventilator and make them really, really sick, to death, so you don't want them to get milk with CMV in it," said Marinelli, who is also a neonatologist at Connecticut Children's Medical Center, in Hartford.
Intriguingly, when the researchers compared the contamination in the purchased breast milk to unpasteurized samples that had been donated to a local breast milk bank, they found the donated samples were less likely to contain harmful germs.
Researchers say there may be a couple of reasons for the differences. The first is that milk banks carefully educate donors about safe collection and handling of breast milk. Some websites also post safe-sharing guidelines, but buyers have no way to know whether sellers are actually following them.
And previous studies have found that almost one in three mothers never cleans her breast pump.
"What this experience has taught us is that when you open the box of milk that you've bought, there's really nothing that can reassure you that the milk is safe," said study researcher Sarah Keim, principal investigator in the Center for Biobehavioral Health at Nationwide Children's Hospital in Columbus, Ohio.
Keim said the researchers logged all sorts of information about the milk they got to find patterns of problems that might signal contamination. Some of the milk was shipped with gel packs or dry ice to keep it cold, but that didn't seem to matter. The temperature of the milk when it reached the researchers didn't make a difference. The kind of container and its condition also didn't seem to play a role, nor did promises of healthy, fresh, or organic milk in ads placed by sellers.
"There was nothing that was helpful," Keim said. "You just don't know what you're getting."
In addition to bacteria and viruses, milk can contain traces of drugs and other environmental contaminates, like cigarette smoke.
Profit may also have a hand in how safe the milk is. In the 1950s, when blood banks paid people for blood and plasma, studies found that purchased samples were seven to 10 times more likely to carry diseases like hepatitis than donated samples. The theory was that people who needed to sell blood to make money were also less likely to be healthy than those who donated to patients.
"With the monetary piece in this, we're a little worried that people might be incentivized to do things that aren't 100 percent honest and safe," Keim said.
She also said they're in the process of retesting their samples to find out exactly what's in them "because we suspect some of them might not have been 100 percent human milk."
The study is published online Oct. 21 and in the November print issue of Pediatrics.
Milk-sharing advocates point out that women have been helping each other nurse for generations. Before the Internet came into the picture, they say, mothers often relied on other women as wet nurses. And they say there's never been a documented case of a baby getting sick from shared milk.
That's true, Marinelli said, adding, "But do you think a mom who is buying milk off the Internet and her kid gets sick is going to necessarily tell the doctors what she did?"
And she said that most of the kinds of bacteria found in the study would probably cause symptoms like diarrhea, vomiting, listlessness, and in severe cases maybe an all-over infection -- and mothers might not even realize that the milk caused the problem.
For her part, Katie Sweet, who said she was still waiting for the first shipment of purchased breast milk to arrive, said the study left her feeling disappointed. She said she planned to contact her doctor and a friend who is a nurse practitioner to figure out how to proceed.
"I think if you work so hard to seek out milk it would be devastating to have a reaction like that," she said.
To learn more about the use of donor breast milk, head to the U.S. Food and Drug Administration.