An estimated three-quarters of breast milk samples available to purchase through the Internet may be contaminated with high levels of bacteria and even pathogens, according to a new study led by researchers at Nationwide Children’s Hospital. Following a growing trend of sharing breast milk via websites, authors of the study released online Monday in the journal Pediatrics tested samples from two major human milk-sharing sites. They found that 72 percent of the samples had been colonized by Gram-negative bacteria. In addition, 44 percent contained Coliforms, 36 percent contained Streptococcus and three percent contained Salmonella. Only nine samples had no detectable growth. It’s difficult to estimate how many people are buying human milk online, but Dr. Sarah Keim, the lead investigator of the study, estimated that more than 13,000 unique postings – some for sale and some for sharing – were placed on the four main milk-sharing websites in 2011. Although these sites do post guidance on how to minimize health and safety risks, with no oversight of the exchanges, “the onus is on individuals to protect themselves and their children,” reads the study. Unlike milk available from milk banks, these products do not undergo pasteurization. “Bacterial contamination can come from several sources, including poor hand hygiene, unclean parts of the breast pump, and milk containers that are not sanitary,” Keim told Food Safety News. “Warm storage conditions can then facilitate bacterial growth as well.” Keim said the team is currently exploring other possible risks such as exposure to pharmaceuticals and drugs and determining if any of the milk was adulterated in some way, such as being watered down. Researchers initially responded to nearly 500 advertisements selling human milk and eventually received 101 samples to test. To preserve anonymity, transactions were terminated with any seller who asked about the recipient infant or wanted telephone or in-person communication. The study explains that this could have biased the results of the study if the excluded women “were also more careful about hygiene or were less likely to carry viral disease.” Ultimately, Keim said, “Buying milk via the Internet poses numerous risks, and one cannot tell for sure that the milk one receives is safe.” The risk of infection is particularly high for preterm or medically compromised infants. “Because the consequences can be serious, buying milk online is not a good idea,” Keim said. The U.S. Food and Drug Administration does not currently regulate the exchange of human milk, but has warned of the risk of improperly screening a donor and recommends against feeding a baby breast milk acquired through the Internet.