Milk samples are obtained from the patient's mother for analyses of functional antibody against Staphylococcus epidermidis and Staphylococcus aureus; bacterial culture and sensitivity; bacterial colony count; and immunoglobulin and nutrient composition (i.e., energy, protein). Maternal blood samples to measure functional antibody are obtained every 2 weeks throughout hospitalization as long as infant is receiving own mother's milk. Cord blood is obtained at delivery.