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.
Keywords: Emergency Care; Infectious Disease Medicine.
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