[Incidence and risk factors of acute focal bacterial nephritis in children with febrile urinary tract infections].

Objective: To determine the incidence of acute focal bacterial nephritis (AFBN) in children with febrile urinary tract infections (UTI) and to identify associated risk factors. Methods: A retrospective cohort study included 181 children hospitalized with febrile UTI at Fujian Children's Hospital from April 2021 to September 2023. Demographic data, clinical manifestations, and laboratory findings were collected. Patients were categorized into AFBN group and non-AFBN group based on AFBN diagnosis. The incidence of AFBN within this febrile UTI cohort was determined. The diagnostic value for pre-antibiotic blood white blood cell (WBC) count and C-reactive protein (CRP) level, along with post-treatment fever duration and pyuria duration for AFBN was evaluated using the area under curve (AUC) of the receiver operating characteristic (ROC). Results: The cohort comprised 181 children with febrile UTI (100 boys and 81 girls), age of 0.6 (0.3, 1.0) years. Eleven patients (6.1%) were diagnosed with AFBN. For predicting AFBN, the AUC was 0.71 (95%CI 0.55-0.85, P=0.026) for pre-antibiotic WBC count and 0.80 (95%CI 0.71-0.90, P=0.001) for pre-antibiotic CRP level, with optimal cutoff values of 16.0×109/L and 80.1 mg/L, respectively. For post-treatment parameters, the AUC was 0.79 (95%CI 0.69-0.92, P=0.001) for fever duration and 0.84 (95%CI 0.72-0.97, P<0.001) for pyuria duration, with optimal cutoff values of 1.9 d and 5.5 d, respectively. The combination of pre-antibiotic WBC count >16.0×109/L and CRP>80.1 mg/L yielded a sensitivity of 0.73 and a specificity of 0.86 for AFBN prediction. Similarly, the combination of post-treatment fever duration ≥2 d and pyuria duration >5 d demonstrated a sensitivity of 0.82 and specificity of 0.88. Conclusions: AFBN incidence was 6.1% in this cohort of children with febrile UTI. AFBN should be highly suspected in febrile UTI children presenting with either a pre-antibiotic WBC count >16.0×109/L and CRP >80.1 mg/L, or a post-treatment fever duration ≥2 d and pyuria duration >5 d.