Febrile Urinary Tract Infection With Negative Initial Urine Culture

Febrile urinary tract infection (UTI) is a common bacterial infection in young infants. The diagnosis of febrile UTI is confirmed by a urine culture obtained via catheterization. UTI is generally considered unlikely when the bacterial colony count does not meet the diagnostic threshold. We identified infants diagnosed with febrile UTI at our institution who underwent urine testing multiple times during the same febrile episode. We summarized the clinical characteristics of patients whose initial urine culture was below the UTI diagnostic threshold but who subsequently had a positive urine culture during the same febrile episode. Five infants with febrile UTI were identified who had a low colony count in the initial urine test, followed by a positive urine culture during the same febrile episode. In most patients, the initial urine samples were obtained within several hours of fever onset. Two patients had known vesicoureteral reflux, 3 had a prior history of UTI, and 2 were younger than 3 months of age at presentation. Febrile UTI should not be excluded solely on the basis of an initial urine culture below the diagnostic threshold for UTI, especially when the urine sample is obtained in the early phase of fever.