Bacterial growth in cultures of bag urine specimens are more likely to be falsely positive in young children with suspected urinary tract infection (UTI) due to contamination with perineal flora. A bag urine culture cannot therefore be used to establish the diagnosis of UTI and may lead to overtreatment. Although a negative bag culture would rule out a UTI, a positive culture requires confirmation by a more specific method, incurring substantial delay. Cultures of urine specimens obtained by catheterization or suprapubic aspiration are more specific and as such are preferred as the routine method of urine collection in non-toilet trained children. Clean-catch, the standard technique of urine collection for toilet-trained children, is a non-invasive method sometimes attempted in infants but is also associated with relatively high rates of contamination.
Sources:
Subcommittee On Urinary Tract Infection, Steering Committee On Quality Improvement And Management et al. Urinary Tract Infection: Clinical Practice Guideline for the Diagnosis and Management of the Initial UTI in Febrile Infants and Children 2 to 24 Months. Pediatrics. Aug 2011, 595-610. PMID: 21873693.
Robinson JL, et al. Urinary tract infections in infants and children: Diagnosis and management. Paediatrics & Child Health. 2014;19(6):315-19. PMCID: PMC4173959.
Labrosse M, et al. Evaluation of a New Strategy for Clean-Catch Urine in Infants. Pediatrics Aug 2016, e20160573. PMID: 27542848.
Tosif S, et al. Contamination rates of different urine collection methods for the diagnosis of urinary tract infections in young children: An observational cohort study. J Paediatr Child Health. 2012 Aug;48(8):659-64. PMID: 22537082.