Urinary tract infection (UTI) in children is the most common disease during the infantile period, therefore early diagnosis and treatment are important. Pyuria is a useful clinical parameter for the initial diagnosis of a UTI. In this study we aimed to compare the clinical, laboratory, and imaging findings in relation to the duration of pyuria in infants with UTIs.

Three hundred seventy-four infants <12 months of age who were admitted between January 1995 and December 2005 for the first episode of a febrile UTI were retrospectively reviewed. Patients were divided into two groups according to the duration of pyuria as follows: group 1, pyuria resolved <3 days after initial treatment; and group 2, pyuria lasted at least 3 days after initial treatment.

There were no significant differences between the two groups in relation to gender, age, total duration of fever, and organisms in the urine. Group 2 had a significantly higher peripheral blood leukocyte count (14,360.86±5,526.16 cells/mm³ vs. 11,822.55±5,687.26 cells/mm³, P<0.001), erythrocyte sedimentation rate (32.81±19.34 mm/hr vs. 23.74±20.43 mm/hr, P<0.001), and C-reactive protein (6.84±5.68 mg/dL vs. 3.78±3.99 mg/dL, P<0.001) than group 1. There was a significantly higher incidence of hydronephrosis and a higher grade of vesicoureteral reflux (VUR) in group 2 compared to group 1.

In infants with UTI, pyuria of longer duration is related to severe UTI and higher grade VUR, therefore aggressive radiologic studies may be necessary.