Background and objectives: Guidelines from the American Academy of Pediatrics define urinary tract infection (UTI) as the growth of greater than 50,000 ufc/mL of a single bacterium in a urine culture with a positive urine dipstick or with a urinalysis associated. Our objective was to evaluate the adequacy of this cutoff point for the diagnosis of UTI in young febrile infants.
Methods: Subanalysis of a prospective multicenter study developed in RISeuP-SPERG Network between October 11 and September 13. To carry out the study, it was performed a comparison of analytical and microbiological characteristics of patients younger than 90 days with fever without focus, taking into account the results of urine dipstick and urine culture.
Results: Of a total of 3333 infants younger than 90 days with fever without focus which were included in the study, 538 were classified as UTI in accordance with American Academy of Pediatrics' guidelines. These patients were similar to those who had a positive urine dipstick and a urine culture yielding of 10,000 to 50,000 ufc/mL, and they were different from those who had a normal urine dipstick and a urine culture >50,000 ufc/mL, being focused on the isolated bacteria and blood biomarkers values. Forty-five invasive bacterial infections were diagnosed (5.9% of the 756 with a urine culture >10,000 ufc/mL). Half of the infants with a normal urine dipstick diagnosed with invasive bacterial infections were younger than 15 days.
Conclusions: It might be inadequate to use a threshold of 50,000 cfu/mL to consider a urine culture as positive in young febrile infants given the fact that it would misdiagnose several UTIs.