RESUMEN
OBJECTIVE: To analyse the performance of the urine Gram stain for predicting a positive urine culture (UC) in young infants with fever without source (FWS) and pyuria. DESIGN: Observational study; secondary analysis of a prospective registry-based cohort study. SETTING: Paediatric emergency department; tertiary teaching hospital. PATIENTS: Infants ≤90 days old with FWS, pyuria and urine Gram stain requested seen between 2010 and 2022. MAIN OUTCOME MEASURE: Performance of the Gram stain, defined as positive if any bacteria were seen, for predicting urinary tract infection (UTI: UC by urethral catheterisation growing >10 000 CFU/mL of a single bacterial pathogen). RESULTS: Among 367 febrile infants with pyuria, 281 (76.6%) had a positive Gram stain and 306 (83.3%) had a positive UC (277; 90.5% Escherichia coli).Rates of positive UC in patients with positive and negative Gram stains were 97.2% and 38.4%, respectively (p<0.01), showing a sensitivity of 89.2% (95% CI: 85.2% to 92.2%) and a specificity of 86.9% (95% CI: 76.2% to 93.2%). Sensitivity was lower for diagnosing UTIs caused by bacteria other than E. coli (69.0% vs 91.3% for UTIs caused by E. coli; p<0.01).Two (2.1%) of the 86 infants with negative Gram stains were diagnosed with bacteraemia unrelated to a UTI (Streptococcus pneumoniae and Staphylococcus aureus). CONCLUSIONS: Around a third of infants with pyuria and a negative Gram stain will eventually be diagnosed with a UTI. These patients have a higher rate of UTIs caused by bacteria other than E. coli. Bacterial infections other than UTIs should also be considered in such cases.
RESUMEN
OBJECTIVES: To analyze the performance of commonly used blood tests in febrile infants ≤90 days of age to identify patients at low risk for invasive bacterial infection (bacterial pathogen in blood or cerebrospinal fluid) by duration of fever. METHODS: We conducted a secondary analysis of a prospective single-center registry that includes all consecutive infants ≤90 days of age with fever without a source evaluated at 1 pediatric emergency department between 2008 and 2021. We defined 3 groups based on caregiver-reported hours of fever (<2, 2-12, and ≥12) and analyzed the performance of the biomarkers and Pediatric Emergency Care Applied Research Network, American Academy of Pediatrics, and Step-by-Step clinical decision rules. RESULTS: We included 2411 infants; 76 (3.0%) were diagnosed with an invasive bacterial infection. The median duration of fever was 4 (interquartile range, 2-12) hours, with 633 (26.3%) patients with fever of <2 hours. The area under the curve was significantly lower in patients with <2 hours for absolute neutrophil count (0.562 vs 0.609 and 0.728) and C-reactive protein (0.568 vs 0.760 and 0.812), but not for procalcitonin (0.749 vs 0.780 and 0.773). Among well-appearing infants older than 21 days and negative urine dipstick with <2 hours of fever, procalcitonin ≥0.14 ng/mL showed a better sensitivity (100% with specificity 53.8%) than that of the combination of biomarkers of Step-by-Step (50.0% and 82.2%), and of the American Academy of Pediatrics and Pediatric Emergency Care Applied Research Network rules (83.3% and 58.3%), respectively. CONCLUSIONS: The performance of blood biomarkers, except for procalcitonin, in febrile young infants is lower in fever of very short duration, decreasing the accuracy of the clinical decision rules.
