Case records of all newborns with positive blood cultures were reviewed for 51 consecutive months to determine the clinical significance of a negative culture at 48 hrs. incubation. All cultures were monitored by the early subculture technique. Patients were considered to have clinically documented bacteremia if: (A) one blood culture was positive plus the same organism grew from a second blood culture (80 pts.), or from CSF, abscess, surgical, or urine cultures (14 pts.); (B) one positive blood culture grew a usual pathogen and the patient responded to antibiotic therapy appropriate for that organism (17 pts.). Records were available for 204 cultures on 158 neonates. Organisms growing from 111 (55%) represented significant bacteremia. The remaining 93 (45%) were considered contaminants (only one culture positive, and symptoms resolving without appropriate antibiotic therapy).
96% of all clinically significant blood cultures from newborns not pretreated with antibiotics were positive by 48 hrs. To reduce the risks of antibiotic use in the nursery, serious consideration should be given to discontinuing therapy in newborns with negative blood (and other) cultures at 48 hrs.