OBJECTIVES: To derive and internally validate a prediction model for the identification of febrile infants #60 days old at low probability of invasive bacterial infection (IBI). METHODS: We conducted a case-control study of febrile infants #60 days old who presented to the emergency departments of 11 hospitals between July 1, 2011 and June 30, 2016. Infants with IBI, defined by growth of a pathogen in blood (bacteremia) and/or cerebrospinal fluid (bacterial meningitis), were matched by hospital and date of visit to 2 control patients without IBI. Ill-appearing infants and those with complex chronic conditions were excluded. Predictors of IBI were identified with multiple logistic regression and internally validated with 10-fold cross-validation, and an IBI score was calculated. RESULTS: We included 181 infants with IBI (155 [85.6%] with bacteremia without meningitis and 26 [14.4%] with bacterial meningitis) and 362 control patients. Twenty-three infants with IBI (12.7%) and 138 control patients (38.1%) had fever by history only. Four predictors of IBI were identified (area under the curve 0.83 [95% confidence interval (CI): 0.79-0.86]) and incorporated into an IBI score: age ,21 days (1 point), highest temperature recorded in the emergency department 38.0-38.4°C (2 points) or $38.5°C (4 points), absolute neutrophil count $5185 cells per mL (2 points), and abnormal urinalysis results (3 points). The sensitivity and specificity of a score $2 were 98.8% (95% CI: 95.7%-99.9%) and 31.3% (95% CI: 26.3%-36.6%), respectively. All 26 infants with meningitis had scores $2. CONCLUSIONS: Infants #60 days old with fever by history only, a normal urinalysis result, and an absolute neutrophil count ,5185 cells per mL have a low probability of IBI. WHAT'S KNOWN ON THIS SUBJECT: Commonly used risk-stratification criteria for febrile infants were either developed .2 decades ago in studies that included relatively few infants with bacteremia and/or bacterial meningitis or include procalcitonin, which is not readily available in some hospitals. WHAT THIS STUDY ADDS: A newly derived score is highly sensitive for the identification of non-ill-appearing febrile infants #60 days old with invasive bacterial infection. Infants with fever by history only, normal urinalysis results, and an absolute neutrophil count ,5185 cells per mL had a low probability of infection.

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To evaluate the Rochester and modified Philadelphia criteria for the risk stratification of febrile infants with invasive bacterial infection (IBI) who do not appear ill without routine cerebrospinal fluid (CSF) testing. METHODS: We performed a case-control study of febrile infants ≤60 days old presenting to 1 of 9 emergency departments from 2011 to 2016. For each infant with IBI (defined as a blood [bacteremia] and/or CSF [bacterial meningitis] culture with growth of a pathogen), controls without IBI were matched by site and date of visit. Infants were excluded if they appeared ill or had a complex chronic condition or if data for any component of the Rochester or modified Philadelphia criteria were missing. RESULTS: Overall, 135 infants with IBI (118 [87.4%] with bacteremia without meningitis and 17 [12.6%] with bacterial meningitis) and 249 controls were included. The sensitivity of the modified Philadelphia criteria was higher than that of the Rochester criteria (91.9% vs 81.5%; P = .01), but the specificity was lower (34.5% vs 59.8%; P < .001). Among 67 infants >28 days old with IBI, the sensitivity of both criteria was 83.6%; none of the 11 low-risk infants had bacterial meningitis. Of 68 infants ≤28 days old with IBI, 14 (20.6%) were low risk per the Rochester criteria, and 2 had meningitis. CONCLUSIONS: The modified Philadelphia criteria had high sensitivity for IBI without routine CSF testing, and all infants >28 days old with bacterial meningitis were classified as high risk. Because some infants with bacteremia were classified as low risk, infants discharged from the emergency department without CSF testing require close follow-up.