In the study, “Microbial Contamination of Human Milk Purchased via the Internet,” published in the November 2013 issue of Pediatrics (published online Oct. 21), researchers purchased 102 cross-sectional samples of human milk through a popular U.S. milk-sharing website.

The milk samples were sent to a rented mail box in Ohio, and later compared with samples of unpasteurized, donated milk obtained through a milk bank. Seventy-four percent of the Internet milk samples were colonized with high bacterial counts overall, or had at least some Gram-negative bacteria; and 64 percent of the Internet samples tested positive for staphylococcus, compared to 25 percent of the milk bank samples. Three of the Internet samples were contaminated with Salmonella. The high overall bacterial growth and frequent contamination with disease-causing bacteria in the Internet milk reflected poor collection, storage or shipping practices, according to the study authors.

Infants consuming human milk purchased via the Internet are at risk for negative outcomes, especially premature infants and those with compromised immune systems. The study authors recommend lactation support for mothers who want to provide breast milk to their infants but who have difficulty making enough. Women who have extra milk should consider donating to a milk bank.