Incidence and Predictors of Serious Bacterial Infections Among 57- to 180-Day-Old Infants

BACKGROUND: Numerous researchers have investigated fever in infants <2 months of age. However, the etiology of fever and usefulness of screening tests in older (2-6 months) infants is not well studied. METHODS: This was a prospective study of febrile infants 57-180 days old. Evaluation included blood and urine tests and direct fluorescent antibody (DFA) of nasal swabs for respiratory viruses. Additional studies were performed at the discretion of managing clinicians. RESULTS: Serious bacterial illness (SBI) was diagnosed in 44 (10.3%) of 429 infants: 41 with bacteruria and 4 with bacteremia (1 infant had concurrent Escherichia coli bacteruria and bacteremia). Lumbar puncture, performed in 58 (13.5%) infants, revealed no cases of bacterial meningitis. DFAs were positive in 163 (38.0%) infants: the majority were respiratory syncytial virus or influenza A. SBI was noted in 4.9% of infants with positive DFA. Age and height of fever were not significant predictors of SBI. White blood cell count (17.1 K/mm3 vs 12.4 K/mm3) and CRP (2.6 mg/dL vs 0.9 mg/dL) were elevated in infants with SBI, as was the Yale Observation Score (9.4 vs 8.0). CONCLUSIONS: A substantial proportion (10.3%) of older febrile infants has SBI. In the postpneumococcal vaccine era, only 1 infant had pneumococcal disease; bacteremia was noted in 0.9%. Bacteruria is commonly associated with fever in this age range. Infants older than 8 weeks remain at risk for bacteremia and bacteruria, regardless of positive DFA or other apparent source of fever. CRP is a better indicator than white blood cell count, but no single ideal indicator of SBI was identified for this age group.