Urinary tract infection in infants: the significance of low bacterial count

Pediatr Nephrol. 2016 Feb;31(2):239-45. doi: 10.1007/s00467-015-3199-y. Epub 2015 Sep 10.


Background: In national guidelines for urinary tract infection (UTI) in children, different cut-off levels for defining bacteriuria are used. In this study, the relationship between bacterial count in infant UTI and inflammatory parameters, frequency of vesicoureteral reflux (VUR), kidney damage, and recurrent UTI was analyzed.

Methods: We conducted a population-based retrospective study of 430 infants age <1 year with symptomatic UTI diagnosed by suprapubic aspiration. Clinical and laboratory parameters, findings on voiding cystourethrography and (99m)technetium dimercapto-succinic acid scintigraphy, and frequency of recurrence were related to bacterial count at the index UTI.

Results: Eighty-three (19%) infants had bacterial counts <100,000 colony-forming units (CFU)/ml and 347 (81%) had ≥100,000 CFU/ml. There was similar frequency of VUR (19% in both groups), kidney damage (17 and 23%, p = 0.33) and recurrent UTI (6 and 12%, p = 0.17) in the low and high bacterial group. Non-E. coli species were more prevalent (19 versus 6%, p = 0.0006) and mean C-reactive protein was lower (50 vs. 79 mg/l, p <0.0001) in the low bacteria group.

Conclusions: UTI with low bacterial count is common and of importance since it may be associated with VUR and renal damage. Non-E. coli species and low inflammatory response were more prevalent in UTI with low bacterial count.

Keywords: Bacterial count; Children; Infants; Kidney damage; Urinary tract infection; Vesicoureteral reflux.

MeSH terms

  • Bacteria / isolation & purification
  • Bacterial Load / methods*
  • Colony Count, Microbial
  • Female
  • Humans
  • Infant
  • Infant, Newborn
  • Kidney Diseases / diagnosis
  • Kidney Diseases / microbiology*
  • Male
  • Recurrence
  • Retrospective Studies
  • Technetium Tc 99m Dimercaptosuccinic Acid
  • Urinary Tract Infections / diagnosis
  • Urinary Tract Infections / microbiology*
  • Vesico-Ureteral Reflux / diagnosis
  • Vesico-Ureteral Reflux / microbiology*


  • Technetium Tc 99m Dimercaptosuccinic Acid