Bacterial infections in infants 60 days and younger: epidemiology, resistance, and implications for treatment.

OBJECTIVE To establish what might be more optimal initial antibiotic therapy for suspected invasive bacterial infections in infants 60 days or younger who are evaluated in the emergency department (ED). SETTING Urban university-affiliated pediatric referral center with an average yearly ED census of 52000 visits during the study period. DESIGN AND METHODS We assembled a retrospective case series of all positive blood, urine, and cerebrospinal fluid cultures in children 60 days or younger from January 1, 1994, through December 31, 1997, obtained from both inpatients and patients initially evaluated in the ED. From this case series we determined the frequency of bacterial pathogens responsible for such infections in this age group. Pathogens were defined as group B streptococcus, various enteric gram-negative rods (GNRs), Listeria monocytogenes, enterococcus, Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae type B, and Staphylococcus aureus. A subgroup analysis was performed to determine resistance patterns among the GNRs isolated from patients evaluated in the ED. RESULTS A total of 367 pathogens were isolated: 187 (51.0%) in the neonatal intensive care unit, 153 (41.7%) in the ED, 20 (5.4%) in the inpatient wards, and 7 (1.9%) in the pediatric intensive care unit. Of the 121 pathogens isolated from 120 ED patients that were eligible for review, 94 (77.7%) were in the urine only, 16 (13.2%) in blood only, 4 (3.3%) in cerebrospinal fluid only, 3 (2.5%) in blood and cerebrospinal fluid, and 4 (3.3%) in blood and urine. Organisms isolated included GNRs (n = 96, 79.3%), group B streptococcus (n = 14, 11.6%), enterococcus (n = 7, 5.8%), S. pneumoniae (n = 3, 2.5%), and N. meningitidis (n = 1, 0.8%). No Listeria were isolated. Of the 96 GNRs isolated, 60 (62.5%; 95% confidence interval, 52.8%-72.1%) were ampicillin resistant. All were sensitive to gentamicin sulfate and cefotaxime sodium. CONCLUSIONS Our results reveal 2 important facts: (1) during a 4-year period, no isolates of Listeria were identified from any patients 60 days or younger; and (2) of the 96 GNRs isolated from patients in the ED, more than 60% were ampicillin resistant. These data suggest that in similar centers with a low incidence of infection with Listeria and high levels of ampicillin resistance among GNRs, empiric use of ampicillin as part of a combination for presumed bacterial infections in patients 60 days or younger initially evaluated in the ED may be neither necessary nor beneficial. Consideration should be given to empiric initial antibiotic therapy using a third-generation cephalosporin with or without gentamicin.