Bacterial contamination of human milk: container type and method of expression

Common questions from nursing women include: is the bacterial contamination of expressed milk different if collected manually versus mechanically and is there a large increase in bacterial contamination if the milk is collected into clean versus sterile containers. Similarly, there are mixed reports, and secondarily confusion, among lactating women regarding the benefit of discarding the initial portion of a milk expression to limit bacterial contamination with skin flora. To answer these concerns, we have measured the number of colony-forming units (CFU)/milliliter in expressed milk from 16 women. The experimental design, used in a randomized fashion with each woman, employed both sterile and clean containers for collection and both the manual and mechanical techniques for milk expression. The number of milk specimens containing greater than 10(4) CFU/ml was not different between those collected in clean versus sterile containers or between those collected with a manual versus a mechanical technique. Finally, the initial milk expressed did not have a significantly greater amount of bacterial contamination than the milk collected later in the milk expression.