When we were in the hospital this weekend with a dehydrated baby we got the diagnosis that she tested positive for rotavirus. They also did a lactoferrin stool sample test which came out positive meaning she also had a bacterial infection like e coli or salmonella. We were prescribed an antibiotic. When we got home we thought how odd that she would get a bad viral and bacterial infection at the same time. A quick good search showed that the lactoferrin test will always be positive in breastfed babies. We called back to the ER and sure enough the test is no good and she doesn't need the antibiotics.

http://www.nphl.org/documents/LactoferrinStoolWBCTestHinrichs-Armbrust.pdf