This study aimed to investigate the predictive factors of concomitant bacteremia occurring in febrile infants who initially presented with pyuria and fever, and were subsequently diagnosed with culture-proven urinary tract infection (UTI). We conducted a retrospective cohort study for January 2010–October 2018 that included infants younger than six months with febrile UTI at a tertiary hospital. The study included 463 patients, of whom 34 had a concomitant bacteremic UTI. Compared to those in the non-bacteremic urinary tract infection (UTI) group, the bacteremic UTI group had a lower mean age; higher levels of C-reactive protein (CRP), delta neutrophil index (DNI, reflects the fraction of immature granulocytes) and blood urea nitrogen (BUN); lower levels of hemoglobin (Hb) and albumin; and a lower platelet count. Vesicoureteral reflux (VUR) was detected nearly twice as often in patients with bacteremic UTI compared to those with non-bacteremic UTI (59.3% vs. 30.6%; P = 0.003). Univariate logistic analyses showed that age ≤90 days; higher DNI, CRP, and creatinine levels; lower Hb and albumin levels; and the presence of VUR were predictors for bacteremic UTI. On multivariate logistic regression analysis, age ≤90 days, higher DNI and CRP levels, and the presence of VUR were independent predictors of bacteremic UTI. The area under the receiver operating characteristic curve of the multivariate model was 0.859 (95% CI, 0.779–0.939; P < 0.001). Age ≤90 days, higher DNI and CRP values may help predict bacteremia of febrile infants younger than 6 months with UTI. Vesicoureteral reflux imaging is also recommended in infants with bacteremic UTI to evaluate VUR.
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