The milk was purchased via advertisements through the one website but each shipment of milk was from a different woman. Below are some comments I shared on Facebook about the study. 
News articles on a study looking at bacterial and viral contamination of breastmilk bought using an internet milk sharing site are starting to pop up. http://www.nbcnews.com/health/75-percent-breast-milk-bought-online-contaminated-analysis-shows-8C11421794?ocid=twitter
I've read the paper. The problem for the authors was that they wanted to obtain milk for testing without revealing that they wanted the milk for an experiment. This required them to hide their identities and everything that they did associated with that made it more and more likely that they would get milk with problems. 
*They had to buy the milk. They could not use the milk gifting sites because they don't allow for anonymity and would require one of the investigators to use their own identity or at least would require the fabrication of an identity (which would not be permitted by ethics committees). This introduced risks inherent to the purchase vs donation re motivation and capacity to safely donate. The altruistic motivation that underlies milk gifting makes milk gifting inherently safer than milk buying.
*The couldn't mention a baby in their request for milk and in fact if the woman selling the milk ever asked about a baby or anything about them at all they stopped communication. They got milk shipped to a PO Box. This behaviour is quite different to how milk recipients usually behave and IMO it made them sound like a man with a milk fettish seeking milk- men do look for milk like this and are mostly given short shrift by donors. This likely would have weeded out any milk sellers who had an altruistic motivation as well as a commercial one.
*They didn't discuss safety of expression or shipping method with the donor (just said, send how you like to) so no due diligence at all. 
*They only got milk shipped which is obviously less desirable than in person donation (which is how the majority work).
Basically all the safety aspects that milk recipients apply to screen their donors- an altruistic motivation; building a relationship of trust based on knowledge of the donor, their situation, their health record; discussion of aspects of safety; in person pick up etc were removed. If the investigators had deliberately sought to screen to get the milk most likely to have problems they could not have done a better job. Breastmilk is robust but it is not magic, if it's not treated properly it can be contaminated. 
All that said, I think it's good to have attention to hygiene given. Indeed in my research I identified that many donors were not following recommended expression practice and recipients were rarely asking about hygiene (http://www.tandfonline.com/doi/abs/10.1080/03004430.2013.772994). It's well known that issues of hygiene are poorly attended to (think of the campaigns necessary to get doctors and nurses to wash their hands in hospitals). It's good to be able to show that it does matter how breastmilk is treated. However, I can see potential for harm even outside of milk sharing, like the mum whose workmates won't let her store her milk in the fridge or the daycare that won't feed ebm to babies because it is dirty dangerous stuff. No thanks to health professionals who seek to demonise breastmilk with misleading alarmist statements!
Karleen Gribble
Australia


> 
> 
> On 10/22/13, Winnie Mading wrote:
> 
> I am confused. The first reports I heard were that it was milk from ONE particular (unnamed) website, which would make one think perhaps it was either one specific donor or handling. However, later reports did not make this distinction and made it sound like the contaminated milk was not one specific source leading to the conclusion that it was from multiple sources. Does anyone know more specifics?
> Winnie Mading, retired
> 
> ***********************************************
> 
> Archives: http://community.lsoft.com/archives/LACTNET.html
> To reach list owners: [log in to unmask]
> Mail all list management commands to: [log in to unmask]
> COMMANDS:
> 1. To temporarily stop your subscription write in the body of an email: set lactnet nomail
> 2. To start it again: set lactnet mail
> 3. To unsubscribe: unsubscribe lactnet
> 4. To get a comprehensive list of rules and directions: get lactnet welcome
> 
>             ***********************************************
> 
> Archives: http://community.lsoft.com/archives/LACTNET.html
> To reach list owners: [log in to unmask]
> Mail all list management commands to: [log in to unmask]
> COMMANDS:
> 1. To temporarily stop your subscription write in the body of an email: set lactnet nomail
> 2. To start it again: set lactnet mail
> 3. To unsubscribe: unsubscribe lactnet
> 4. To get a comprehensive list of rules and directions: get lactnet welcome


             ***********************************************

Archives: http://community.lsoft.com/archives/LACTNET.html
To reach list owners: [log in to unmask]
Mail all list management commands to: [log in to unmask]
COMMANDS:
1. To temporarily stop your subscription write in the body of an email: set lactnet nomail
2. To start it again: set lactnet mail
3. To unsubscribe: unsubscribe lactnet
4. To get a comprehensive list of rules and directions: get lactnet welcome