A 37-week-old infant was delivered by cesarean section and discharged from a Connecticut hospital when he was 10 days old. Two days later he was lethargic and had a fever. When he was readmitted to the hospital, he had multiple brain abscesses caused by Citrobacter diversus. After a prolonged illness, the baby died. A second infant with a normal pregnancy and delivery died of C. diversus meningitis after a short illness. Nine infants in the hospital nursery had umbilical cord colonization by C. diversus. Environmental cultures were negative for hospital equipment. How would you go about making a plan for identifying the source of infection and preventing further infection?