Desperate for breast milk, some new mothers who can't nurse their babies are turning to online sources, typically strangers with ample supplies. But a new study finds that human milk bought and sold on the Internet may be contaminated — and dangerous.

Nearly 75 percent of breast milk bought through the site was tainted with high levels of disease-causing bacteria, including germs found in human waste.

That’s according to Sarah A. Keim, a researcher at Nationwide Children’s Hospital in Columbus, Ohio, where her team purchased more than 100 samples of human milk last year, compared them to unpasteurized samples donated to a milk bank and then tested them for safety.

“I can’t think of something you can buy online where you have less ability to validate the quality,” Keim told NBC News. “Even frozen milk was just as contaminated as thawed milk. There wasn’t a whole lot recipients can rely on to know that it’s OK.”

Keim decided to analyze breast milk samples after noticing more online sites offering human milk to buy, sell or donate. That's far different from the network of organized milk banks that typically provide screened and pasteurized donor milk to babies with medical conditions.

In 2011, as many as 13,000 people posted on the four top sites offering to broker milk deals, Keim said. Most postings were from new moms who couldn’t produce enough milk to feed their babies themselves but wanted the benefits of breast milk.

But what the researchers found was worrisome: more colonies of Gram-negative bacteria including coliform, staphylococcus and streptococcus bacteria in the milk purchased online, and, in about 20 percent of samples, cytomegalovirus, or CMV, which can cause serious illness in premature or sick babies. The contamination was associated with poor milk collection, storage or shipping practices, the analysis showed.

“We were very surprised by our findings,” said Keim. “Besides bacterial contamination and viruses that could be in the milk, you could be exposing your infant to chemical contaminants, pharmaceuticals or drugs as well.”

Representatives of, a corporation based in Incline Village, Nev., did not respond directly to the reports of contamination. But after being contacted by NBC News, website officials said they intend to halt informal breast milk exchanges and revamp their organization.

"We have made the decision to transition away from offering breast milk classified ads and in the near future completely remove them," site founder Glenn Snow said in a statement.

Instead, officials said they are working to form a new milk bank program, Milk for Babies, that would partner with a laboratory to offer screened milk while still permitting donors to be reimbursed.

"We are convinced that a more safety-centered approach must be taken to secure milk sharing," officials added.

Still, the new study is causing an uproar in the larger breast milk world, where advocates of existing non-commercial milk-sharing sites say the report unfairly tarnishes efforts to boost the use of human milk for all babies, even when their moms don’t have enough.

Health officials routinely urge women to nurse their babies exclusively for the first six months and along with other foods for the first year. About 77 percent of U.S. babies are fed their mother’s milk at least once, according to the Centers for Disease Control and Prevention.

“A blatant attack on women attempting to feed their babies is cruel and you should feel ashamed of yourself for spreading misinformation,” Khadijah Cisse, a midwife who founded MilkShare, a portal for connecting women cited in the new research, said in an email to NBC News. “Anyone can type up any bit of lies they want and make claims. Breast milk is supposed to contain bacteria.”

Any feeding system except a mother breast-feeding her own child carries some risk, said Shell Walker, founder of Eats on Feets, a milk-sharing portal. “There’s not a single feeding method outside of that closed biological system that doesn’t warrant close monitoring,” she said.

Emma Kwansica, founder of Human Milk 4 Human Babies, says that the women who share milk in 130 communities in 52 countries aren’t strangers engaged in commerce.

“Peer-to-peer milk-sharing is really about families sharing at a hyper-local level. This study could not have been more opposite of what our moms are doing in the world today,” she said. “If there are babies getting sick from milk sharing, I would know. There are no sick babies.”

The problem, Keim said, is that the milk samples exchanged contained not only healthful bacteria, which are necessary, but high levels of bacteria that could cause harm.

“The pathogenic bacteria, those are the ones that are the most concerning,” she said. All of the sharing sites urge women to collect, store and send milk in sanitary ways and to offer medical proof that the milk is safe. It's not clear, however, how many suppliers follow those instructions.

Keim's team sought samples through classified ads on the OnlyTheBreast site, where they were able to buy milk for between 50 cents and $3 an ounce.

They didn't obtain samples from the sharing sites because of the need for anonymity, but Keim said contamination is possible whenever strangers offer to supply — and, often, ship — unscreened milk.

Of 495 inquiries sent, 191 sellers never replied and 41 stopped corresponding after one reply, Keim wrote. Some 79 sellers agreed to send milk but never followed through and eight accepted payment but didn’t send the promised product.

Of the 101 samples analyzed, 72 were contaminated with bacteria and would not have met criteria for feeding without pasteurization set by the Human Milk Banking Association of North America, or HMBANA.

That’s a network of a dozen milk banks in the U.S. and Canada that supply donor milk, typically through health care providers and hospitals. Because the supply is scarce, the banked milk is limited to use in premature and medically fragile babies through medical prescriptions, said Kim Updegrove, president of HMBANA.

All donors are strictly screened and medically tested, and the milk is pasteurized to prevent contamination that could harm a baby, said Updegrove. That causes some slight loss of nutrition, she acknowledges, but reduces risk.

“I don’t think that the general public understands human milk as a bodily fluid that can relay dangerous bacteria and viruses,” she said.

The federal Food and Drug Administration and the American Academy of Pediatrics both warn women not to feed babies breast milk acquired directly from individuals or through the Internet.

Breast milk can transmit infections such as HIV and tuberculosis and can also pass on prescription or illicit drugs. Those risks, combined with the evidence of harmful bacteria, should make new moms think twice about buying milk from strangers, Updegrove said.

“I long to have people view this the way that they view blood products,” she said. “You would never say, ‘I’m a little bit anemic,’ and hand off the tubing.”

The trouble is that women who can’t breastfeed or produce enough milk themselves have few options unless their babies are sick enough to receive milk from a bank, which typically costs between $3.50 to $6 an ounce.

Allison Jones, 35, of Columbus, Ohio, wasn’t able to make enough breast milk for her son, Charlie, who was born more than three months prematurely in May weighing 1 pound, 2.3 ounces. Because he was so early, he was able to obtain milk through a local bank, but if that weren’t an option, she might have considered looking online.

“I can definitely see the appeal,” she said. “We’re told breast milk is fantastic — and it is. But you don’t really know the person donating.”

New mothers who have problems nursing should work with their pediatricians to find other options. Lactation experts can help resolve many feeding problems, Updegrove said.

If that doesn’t help, Updegrove says commercial formula, though not ideal, is a better option than potentially unscreened breast milk from an unknown source.

“While it’s certainly not ideal, if you have a healthy, full-term infant, that infant is likely to do just fine on formula,” she said. “I long to have people see breast milk as a bodily fluid that contains all the benefits, but all the risks, of other bodily fluids.”

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